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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / September 2007Hot vs. cold oil change logic
If you run an engine to its maximum temperature and let it sit overnight for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an immediate hot oil change and letting it drain for the usual 10 to 30 minutes? Some people say they wait much longer but I don't find it practical. If I am correct, the main issue seems to be evacuating oil from the pan if the engine block is drained as best it can be. I'm not convinced that "stirring up" pan sludge by warming the engine will put it "back into suspension" if the oil and filter wasn't capable of holding it already. You're just spreading any (mobile) particles back into the engine channels. Then, you're left with a much shorter drain time (vs. overnight) to get it all back down into the pan. What's the real point? It seems that any sludge stuck to the bottom of the pan is not going to move much, regardless of whether the oil is hot or cold ("cold" meaning ambient temperature; same temperature you pour new into the engine at). What is the real value of doing a hot oil change if it only allows a fraction of the time for oil to drain back from the engine block? The oil can only leave through one hole in the bottom of the pan, so shouldn't it be gathered close to that hole before you start? Why stir it up again if true sludge isn't movable? When I pour new oil into an engine on a warm day, it seems to flow quite well, contrary to the notion that anything below scalding will creep like molasses. Used oil is thinner, if anything, so flow rates should be similar. I've exclusively done hot oil changes but I'm reconsidering. Hot vs. cold seems to come down to how well you can evacuate the pan, and how much MOVABLE sludge is actually there. At worst, you'd be left with a thin film of "cold" oil on top of pan sludge that probably wasn't going to move anyway. At least that's my theory. Has anyone done serious experiments on this? Jack P.S. The ideal method would be to drain the engine AND pan overnight after the engine is hot, but that takes planning and isn't always practical. With any method, opening the oil cap to break suction should help it flow better. > If you run an engine to its maximum temperature and let it sit overnight > for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an > immediate hot oil change and letting it drain for the usual 10 to 30 > minutes? Some people say they wait much longer but I don't find it > practical. I think the answer is to not worry about oil. Do you really care about the very end of the engine's life? Will you still be driving it when it's smoking? Will it still be road-legal? Will you not have a better job by then and be able to afford a car that isn't 20 years old? Even if that's all true and you really love your car, you can fix it with a cheap replacement high-milage engine. As long as you change the oil roughly OK and don't thrash it much the engine will almost certainly last longer than the body. nottoooily@hotmail.com wrote in news:1189270630.710553.191560@ 22g2000hsm.googlegroups.com: >> If you run an engine to its maximum temperature and let it sit overnight >> for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an [quoted text clipped - 10 lines] > roughly OK and don't thrash it much the engine will almost certainly > last longer than the body. Thanks for the philosophy but this isn't rec.throwaway.society. I like to get top life from most things I buy. This is a 10 y/o Toyota 4-cyl. with 190k miles. It's doing fine and so is the chassis. I change the oil (synthetic) every 5k to 7k miles and would like to know if hot is really better. I paid cash (new) and have no interest in monthly bills and higher reg. fees and/or insurance. Do you know how many people are strung out on credit for want of new things? The new car high is temporary and other people don't really care what you drive; even though it may boost internal pride. If it does the job, why let it go to pasture? A big boost in MPG would be my main reason for a replacement. Jack > >> If you run an engine to its maximum temperature and let it sit overnight > >> for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an > >> immediate hot oil change and letting it drain for the usual 10 to 30 > >> minutes? Some people say they wait much longer but I don't find it > >> practical. > Thanks for the philosophy but this isn't rec.throwaway.society. I like to At risk of sounding too practical. That stuck stuff in the bottom probably takes many changes to accumulate, and some of it will never be removed by draining. Would an even better idea be to drain it any old way, then occasionally take the pan off and scrub it out? Possibly the time you save doing quick changes will cancel out the time it costs to clean the pan. I doubt you'll get any actual answers from usenet. Its more in the nature of these people to offer annoying advice on how to avoid the problem than a solution on how to solve it ;) Your exactly right about dropping the oil pan and scrubbing it out,,but the original guestion,I believe was about hot vs cold and how long to drain the oil.You can let your car sit for a week with the oil plug out and not one bit of sludge will come out of the pan than did the first 5 or 10 mins.  Signaturechalleno http://www.automotiveforums.com > Your exactly right about dropping the oil pan and scrubbing it out,,but > the original guestion,I believe was about hot vs cold and how long to > drain the oil.You can let your car sit for a week with the oil plug out > and not one bit of sludge will come out of the pan than did the first 5 > or 10 mins. You've skipped the details of my original question/comment. Having used synthetics and done most changes (hot) at 5k miles, I am not worried about sludge, I am suggesting that when you park a car after a good run, the oil has a lot more time to drain (initially hot) from the engine block overnight. It is a thorough drain vs. a 10 or 20 minute rush. After the oil has gathered in the pan, the issue is whether the final step of draining it from the pan is that much different hot vs. cold. I don't think it is but more evidence is needed. This is really an engineering or physics question. Jack > You've skipped the details of my original question/comment. Having used > synthetics and done most changes (hot) at 5k miles, I am not worried about > sludge, I am suggesting that when you park a car after a good run, the oil > has a lot more time to drain (initially hot) from the engine block > overnight. It is a thorough drain vs. a 10 or 20 minute rush. Why not park it after the drive, open the drainplug while hot, and let it sit overnight? Jack, Next oil change take a 100 mile ride on the interstate then come home and change the oil. It will pour out like boiling oil. I once changed oil after a 360 mile trip back from Ohio--- talk about hot oil! Never had sludge in 309,000 miles and I'm not worried about it. I change oil between 3-4000 miles, had the pan off twice in its life & the inside was clean as bare metal can be. happy motoring..... harryface 2005 Park Avenue 61,289 1991 Bonneville 309,899 >>>>If you run an engine to its maximum temperature and let it sit overnight >>>>for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an [quoted text clipped - 10 lines] > the time you save doing quick changes will cancel out the time it > costs to clean the pan. Having pulled the pan off of engines run to *very* high mileage but with modern oils and decent change intervals (7000 miles or less) I can assure you that unless the engine had a problem like the Toyota inadequate PCV system and ensuing sludge, you'll find NOTHING in the pan. Modern oils just don't let gunk accumulate on the bottom of the pan like 60s vintage oils did. If you're going to find any accumulation, it will be up on the top-end around the valve train, where the oil is much hotter, there's less volume and flow of oil, and the PCV system is pulling combustion gasses across the hot components. Even that proved to be quite clean (spotless, in fact) when I replaced the valve cover gaskets on my wife's car (Chrysler 3.5L) at 200,000 miles after a life of using synthetic oil. > nottooo...@hotmail.com wrote in news:1189270630.710553.191560@ > 22g2000hsm.googlegroups.com: [quoted text clipped - 28 lines] > > Jack With synthetic oil regular changes the car will out last you > Thanks for the philosophy but this isn't rec.throwaway.society. I like to > get top life from most things I buy. This is a 10 y/o Toyota 4-cyl. with > 190k miles. It's doing fine and so is the chassis. I change the oil > (synthetic) every 5k to 7k miles and would like to know if hot is really > better. see my previous post - I should have added that my wife's Beretta is a 17 year old car and I've been doing it that way on that car for 10 years - the body is going, but the motor still runs fine. I do it on my race car. I do it on my 2001 Trans Am. I think you're overthinking a simple oil change. Ray > If I am correct, the main issue seems to be evacuating oil from the pan > if the engine block is drained as best it can be. I'm not convinced that > "stirring up" pan sludge by warming the engine will put it "back into > suspension" if the oil and filter wasn't capable of holding it already. Filters catch BIG particles. It's the small stuff we want out of the engine. All modern oils are ashless-dispersants that keep this stuff in suspension rather than letting it settle out, unless it's been sitting a long time. The sludge we want out of the pan is mostly precipitate from water/oil reactions, and it's tight at lower temps. Water gets into the case as combustion gases, which contain water vapor, get past the rings and condense in a cold engine. Short trips are bad for the engine because the water never gets boiled off. > You're just spreading any (mobile) particles back into the engine > channels. Then, you're left with a much shorter drain time (vs. > overnight) to get it all back down into the pan. What's the real point? Cold oil drains more slowly, and sticks to the inside of the pan as well, so that you don't get as much of the heaviest contaminants out of it. Waiting for engine oil to drain back into the pan after running is mostly a waste of time, since any good filter has an anti-drainback valve in it that traps oil in the galleries. Anything that will drain out of the workings will drain quicker if it's hot. So hotter oil will carry more of the crud that has settled in the galleries when you remove the filter and oil runs out of the case. > It seems that any sludge stuck to the bottom of the pan is not going to > move much, regardless of whether the oil is hot or cold ("cold" meaning [quoted text clipped - 4 lines] > be gathered close to that hole before you start? Why stir it up again if > true sludge isn't movable? True sludge is less movable when cold. > When I pour new oil into an engine on a warm day, it seems to flow quite > well, contrary to the notion that anything below scalding will creep like > molasses. Used oil is thinner, if anything, so flow rates should be > similar. I've exclusively done hot oil changes but I'm reconsidering. Hot > vs. cold seems to come down to how well you can evacuate the pan, and how > much MOVABLE sludge is actually there. In a neglected engine there might be significant sludge. In most that I take apart, there's not much sludge; mostly it's varnish, baked- on stuff that won't drain out anyway. > P.S. The ideal method would be to drain the engine AND pan overnight > after the engine is hot, but that takes planning and isn't always > practical. With any method, opening the oil cap to break suction should > help it flow better. Opening the oil cap won't break any suction. The case is vented through the PCV into the intake manifold. It's not a sealed system. Never was. Dan >> If I am correct, the main issue seems to be evacuating oil from the >> pan if the engine block is drained as best it can be. I'm not [quoted text clipped - 10 lines] > vapor, get past the rings and condense in a cold engine. Short trips > are bad for the engine because the water never gets boiled off. As stated, I would make sure the engine is quite hot before letting it settle overnight. If what remains in the pan can't be dragged out by "cold" oil, the cold method is inferior. But I don't know that this has really been tested. I have poured used "cold" (70F+ ambient temp.) oil from a drain container to see how much gets left behind. Whether hot or cold, the remaining film is not hugely different in my tests. It seems that only a few extra tablespoons (if that) should remain in the engine pan using the cold method. I assume the internal shape of a sump is designed for optimum downward flow. You could pour in a half quart of left-over new oil to help push it out. >> You're just spreading any (mobile) particles back into the engine >> channels. Then, you're left with a much shorter drain time (vs. [quoted text clipped - 4 lines] > pan as well, so that you don't get as much of the heaviest > contaminants out of it. But it's hot when you park it and most of the draining into the sump occurs when it's hot. That's why I don't see the point of warming it up again and giving it much less time to drain all over. The "cold" method makes use of time and patience that people lack when they are thrown into a task. > Waiting for engine oil to drain back into the > pan after running is mostly a waste of time, since any good filter has [quoted text clipped - 3 lines] > in the galleries when you remove the filter and oil runs out of the > case. Still, it's HOT when the bulk of the draining occurs after you park it. Time has already done most of the work. It collects in the pan/sump overnight, waiting for you to remove the plug. Gravity has done its work inside the engine block for much longer than most people can wait in dirty clothes. >> It seems that any sludge stuck to the bottom of the pan is not going >> to move much, regardless of whether the oil is hot or cold ("cold" [quoted text clipped - 6 lines] > > True sludge is less movable when cold. I agree there might be some pan sludge carried off better with hot oil, but the question seems to be how much. Below, you say the stuff that sticks is mostly varnish. If sludge stays suspended in the oil and doesn't settle out overnight, the main difference should be viscosity and flow rate from the pan the next day. I could wait an extra 5 or 10 minutes vs. scalding my hand on the oil and filter. A lot of this is about convenience due to engine layout. >> When I pour new oil into an engine on a warm day, it seems to flow >> quite well, contrary to the notion that anything below scalding will [quoted text clipped - 6 lines] > that I take apart, there's not much sludge; mostly it's varnish, > baked- on stuff that won't drain out anyway. That seems to side with my cold change theory, unless sludge would tend to gather without hot changes. >> P.S. The ideal method would be to drain the engine AND pan overnight >> after the engine is hot, but that takes planning and isn't always [quoted text clipped - 4 lines] > through the PCV into the intake manifold. It's not a sealed system. > Never was. Well, I do notice an extra rush of oil when I loosen the cap, though it may be temporary. I also blow into or slap on the opening and some extra oil comes out. Rocking it has some effect also. Jack On issues of oil types, oil changes, and oil filters, you will get little on this newsgroup but personal opinions. Hard data, rigid testing, is hard to come by. My opinion is that a warm or hot drain is better than a cold, because the viscosity is reduced and the oil and dispersed particles will flow out of the engine more easily. Start hot and let it drain overnight, if you wish. That should be the best of all worlds. And I change at 3-4,000 miles, not 5-7,000. In this way I never seem to have varnishing of the engine parts, sludge, and - most of all - premature engine wear and failure. Again, this is opinion and practice, not hard science. Oil changes are damn cheap compared to engine repairs or replacements. > On issues of oil types, oil changes, and oil filters, you will get > little on this newsgroup [quoted text clipped - 6 lines] > reduced and the oil and dispersed particles will flow out of the > engine more easily. That's what tends to be said but I'm challenging it because the engine block is irrelevant if the oil has already drained from it (when it was hot and thin). The whole debate can be limited to what happens when you try to drain the oil pan after the engine blocked is as clean as it will get. > Start hot and let it drain overnight, if you wish. That should be the > best of all worlds. Definitely true but I find that impractical. I like to get automotive work done in one shot. I also don't like to leave a car undriveable overnight in case of emergency. Since the oil would drain (initially hot) into the pan for hours overnight, the whole question can be isolated to a detached pan you run experiments on. All you need is a good amount of used oil and a heater that mimics engine temperatures. Assuming you have an oil pan from an old vehicle to test: 1: Is drainage just a matter of viscosity and flow rate, meaning a longer wait for (air-temperature) oil to drain from the sink? For me, waiting an extra 5 or 10 minutes is worth it vs. dealing with scalding oil and a hard- to-reach filter. 2: Is there loose sludge (not varnish) on the sink walls that only hot oil will remove? If cold oil also carried it away, just more slowly, time would be the main issue. 3: If you change your oil often enough, is sludge a concern in the first place? "Hot oil theory" is based on the idea that the oil is washing or dragging away stuff it couldn't hold in suspension. From what I understand, if your oil/filter isn't suspending stuff you've waited too long anyhow. Any water in the pan should boil off when you next drive a decent distance, so I don't see water as an issue. Acids could be, though. 4: If all the nasty particles are indeed suspended in the oil/filter, what difference should there be aside from waiting longer for "cold" oil to drain? That's how I'm looking at this. Jack You go out and crank your car and let it run for 5 or 10 minutes after it has been sitting all night,,you won't be dealing with scalding hot oil after running your car for a little while,,,*_if_your_theory_was_correct_there_would_be_a_ sack* *_full_plus_thousands_of_10_minute_oil_change_businesses_going_bankrupt._* Signaturechalleno http://www.automotiveforums.com > You go out and crank your car and let it run for 5 or 10 minutes after > it has been sitting all night,,you won't be dealing with scalding hot > oil after running your car for a little > while,,, Why would I just make it lukewarm and send dirty oil back up into the engine block again? The "cold" change lets it drain (initially hot and thin) all night. I would either do it at max. temp. (drain in 20 or so minutes) or max. TIME (drain into pan overnight, then drain pan). > *_if_your_theory_was_correct_there_would_be_a_ sack* > *_full_plus_thousands_of_10_minute_oil_change_businesses_going_bankrupt > ._* I'm not really arguing against hot oil changes, just presenting the idea that cold ones may be equally or more effective. Either way I don't mess with quick lube shops or mechanics in general. I just now did my first "cold" oil change. It was draining from the block all night and I drained the pan in 85F weather today. The volume that came out seemed the same as previous hot changes. It flowed at maybe 70% of the hot rate and actually went quicker since it was already gathered in the pan. I chased it with half a quart of extra (new) oil and let it drain out. Based on color, it seemed to do a good job of purging the remainder in the pan. This is synthetic oil which tends to flow better than regular anyhow. Not dealing with the hot filter (positioned such that it always spills) was a big plus. I'm still undecided as to whether this should become a routine. Jack >> On issues of oil types, oil changes, and oil filters, you will get >> little on this newsgroup [quoted text clipped - 49 lines] > >Jack If someone is really worried about sludge the best thing would be to park it when it's hot, let is sit overnight, drain it, then get some kerosene and shoot the kerosene into the pan thru the drain hole and put the plug in and let it sit for a bit, then drain it back out, then pour a half a quart of some cheap oil in to flush out any remaining kerosene.... or some variation on that kind of routine. Personally, if you think you need to worry about sludge you simply are not keeping up with your oil changes, change it every 6000/6 months and it will never have an oil related problem. > >> On issues of oil types, oil changes, and oil filters, you will get > >> little on this newsgroup [quoted text clipped - 59 lines] > up with your oil changes, change it every 6000/6 months and it will > never have an oil related problem. Some of the old guys used to drain the oil, put the plug back in, fill the sump with diesel fuel or kerosene or ATF, run the engine at idle for a few minutes, and drain again. I've never had the nerve to do that, but I bet it sure would get the engine clean. Might also loosen a lot of crud better left stuck to where it's stuck. Another old guy would mix a spoonful of baking soda with a little oil and dump that into the case every so often. It would neutralize the acids formed when water mixes with oil and make the engine last a lot longer. Modern oils are much better at this sort of thing: cleaning and preventing corrosion. But as the engine wears it starts to get dirtier faster and changing the oil sooner will keep it lasting longer. The trick is to find a balance between the cost of oil and filters and the amount of extra life that oil/filter cost is buying for you. Dan > Some of the old guys used to drain the oil, put the plug back >in, fill the sump with diesel fuel or kerosene or ATF, run the engine >at idle for a few minutes, and drain again. I've never had the nerve >to do that, but I bet it sure would get the engine clean. Might also >loosen a lot of crud better left stuck to where it's stuck. Yes, but back then, oil was a lot more prone to sludging and there were some engine designs that had more sludging issues as well. So doing this every once in a while was probably a good thing. I remember once seeing the valve covers come off of my neighbor's Valiant and seeing enormous amounts of goo inside there. They explained that because there wasn't any oil filter in the engine it tended to sludge up a lot so they just removed the valve covers and wiped it down. It's been a long time since anyone has had to deal with that kind of thing. > Another old guy would mix a spoonful of baking soda with a >little oil and dump that into the case every so often. It would >neutralize the acids formed when water mixes with oil and make the >engine last a lot longer. I don't think this actually worked particularly well, and since the undissolved baking soda is a little abrasive, it might not be a good idea either. > Modern oils are much better at this sort of thing: cleaning >and preventing corrosion. But as the engine wears it starts to get >dirtier faster and changing the oil sooner will keep it lasting >longer. The trick is to find a balance between the cost of oil and >filters and the amount of extra life that oil/filter cost is buying >for you. Yes, BUT modern oils are also better at keeping the combustion by-products in suspension as well. So the oil can be a lot dirtier without causing problems, compared with the oils of the fifties and sixties. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." >On issues of oil types, oil changes, and oil filters, you will get little on >this newsgroup [quoted text clipped - 17 lines] > >Oil changes are damn cheap compared to engine repairs or replacements. There is no need to change it any sooner then roughly every 6000 miles. Your putting way to much thought into changing oil,,, crank it up ,let it run about 5 minutes,shut it off ,pull the plug and let it rip,replace the filter...do this every 3,000 miles,thats all you need to do,,,if the engine burns up, it would of went anyway,,chill out a little,,there's alot more things you could be sweating,,,if you think your engine is full of sludge, change your oil every 500 miles a couple of times. Signaturechalleno http://www.automotiveforums.com > Your putting way to much thought into changing oil\\ Absolutely right, Challeno. It is not rocket science. Change it regularly and frequently, and use a good oil filter. Then go to sleep and dream of Paris Hilton, or whatever. Your day is over. "hls" <hls@nospam.nix> wrote in news:KNGEi.2597$3Y1.1521 @newssvr17.news.prodigy.net: >> Your putting way to much thought into changing oil\\ > [quoted text clipped - 3 lines] > Then go to sleep and dream of Paris Hilton, or whatever. > Your day is over. Pardon my intrusion into rec.autos.slack! I was expecting more replies along the lines of Dan_Thomas'. I also had other maintenance that made it tricky to drive the car that day but it's not worth explaining. Jack "Time for a cool change..." (Little River Band) "Jack" <jack@beanstalk.net> wrote in message > Pardon my intrusion into rec.autos.slack! I was expecting more replies > along the lines of Dan_Thomas'. I also had other maintenance that made it > tricky to drive the car that day but it's not worth explaining. You wouldnt know an exacting answer if you stepped in it, Jackoff. I already told you that you would get opinions here, not hard data. If you cant understand that, do whatever the hell you want. Or pay the thousands of dollars that are necessary to do the engine tests. These tests have been run, but are not available for free. I dont have access to them, nor apparently do you, dipshit > Your putting way to much thought into changing oil,,, crank it up ,let > it run about 5 minutes,shut it off ,pull the plug and let it [quoted text clipped - 3 lines] > your engine is full of sludge, change your oil every 500 miles a couple > of times. Nothing personal, but that mentality is why I still steer clear of American vehicles. Some of us are into precision, not "like, who cares, man!" Besides, the 3,000 mile oil change interval is not only more work, it's been invalidated as too frequent, at least with synthetics. Most owners manuals indicate a 5,000 or 7,500 mile interval for normal driving (soft commuting). I used to believe that 3,000 miles was smart, but if the oil can hold contaminants in suspension for longer, it's overkill. It creates more labor and adds hassle to long road trips. Of course the oil makers and lube shops won't argue with 3,000 miles. Sell, sell, sell! Jack >> Your putting way to much thought into changing oil,,, crank it up ,let >> it run about 5 minutes,shut it off ,pull the plug and let it [quoted text clipped - 18 lines] > >Jack With regular dino oil, 6000 miles/6 months. With Synthetic, 12,000 miles, 12 months. Anything else is overkill unless you have truly unusual operating conditions. The day of the 3000/3 oil change was when oil was crap compared to today's and carburetors poured huge amounts of gas into the oil during startup, gas was full of lead to foul things, and there was a much greater amount of ring blowby letting combustion byproducts into the crankcase and the oil. >> Your putting way to much thought into changing oil,,, crank it up ,let >> it run about 5 minutes,shut it off ,pull the plug and let it [quoted text clipped - 18 lines] > > Jack OVERKILL? From a guy who's debating how to change oil like it's brain surgery, I think you're missing the point. If you change your oil and filter on a regular basis, you'll get 200,000 miles from just about any car today using any oil and filter. BUT.. the people who use the cheap oil and filters are also the ones who never change it. Ray >If you run an engine to its maximum temperature and let it sit overnight >for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an [quoted text clipped - 36 lines] >practical. With any method, opening the oil cap to break suction should >help it flow better. If you are using Synthetic and doing the drains that often it makes no difference whether you do it hot or cold or anything in between. There isn't any sludge in your engine that you need to worry about moving. If you were doing changes every 20K it might be something to worry about but then it would raise the question of "why worry", you are abusing it anyway if you are doing those long intervals. I think this has much in common with the argument about whether to keep your computer on all the time, or to turn it on just when you need it, as far as hard drive reliability and longevity. For both arguments to have lasted as long as they have, the answer must be, "not a lot of difference." If there really were clear advantage to one way or another, the answer would have popped out long ago. So don't worry about it- six to one, half dozen the other. > If you run an engine to its maximum temperature and let it sit overnight > for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an [quoted text clipped - 36 lines] > practical. With any method, opening the oil cap to break suction should > help it flow better. > If you run an engine to its maximum temperature and let it sit overnight > for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an [quoted text clipped - 36 lines] > practical. With any method, opening the oil cap to break suction should > help it flow better. Run the engine, warm it up good and drain/change it. If your thinking that it needs to set a while for the oil to all drain to the bottom of the engine. Consider that on most vehicles there is less than a quart of oil in the pan with the engine running. The rest is circulating in the engine. If you shut the engine off and wait 5 minutes all the oil will be back in the pan. (oh you may miss a teaspoon or two). The sludge and crud will drain better warm as well. Want a demonstration of why? Go and coat your hands with some dirty oil. Now wash them using cold water. Doesn't come off very well. Now use warm water and you will find it works better. The heat allows the surfactants and detergents to work as designed, just like the detergents and surfactants in the oil will work better and keep the crud suspended in the oil. The oil filter does NOT catch it all, only what is in the oil as it goes through the pump. Oh and just because you use a synthetic does NOT mean you cannot have sludge. SignatureSteve W. Near Cooperstown, New York NRA Member Pacifism - The theory that if they'd fed Jeffrey Dahmer enough human flesh, he'd have become a vegan. > Run the engine, warm it up good and drain/change it. If your thinking > that it needs to set a while for the oil to all drain to the bottom of > the engine. Consider that on most vehicles there is less than a quart of > oil in the pan with the engine running. The rest is circulating in the > engine. If you shut the engine off and wait 5 minutes all the oil will > be back in the pan. (oh you may miss a teaspoon or two). There isn't room in the engine for three quarts of oil to "circulate." There might be a pint in the galleries, and the oil in the filter stays in the filter after shutdown. The galleries are no more than a half-inch in diameter, mostly smaller than that, and in the crankshaft they are 3/16" at most. If there was only a quart in the pan the pickup would be sucking air half the time as the vehicle bumped around. > The sludge and crud will drain better warm as well. Want a demonstration > of why? Go and coat your hands with some dirty oil. Now wash them using [quoted text clipped - 3 lines] > will work better and keep the crud suspended in the oil. The oil filter > does NOT catch it all, only what is in the oil as it goes through the pump. filters catch BIG stuff, like 10 microns or bigger. The smallest stuff stays in the oil, accumulates there, and thickens it. Dan > If you run an engine to its maximum temperature and let it sit overnight > for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an > immediate hot oil change and letting it drain for the usual 10 to 30 > minutes? Some people say they wait much longer but I don't find it > practical. [...] > At worst, you'd be left with a thin film of "cold" oil on top of pan > sludge that probably wasn't going to move anyway. At least that's my > theory. Has anyone done serious experiments on this? Engine oils really do hold solids in suspension. I've tested this, though not very scientifically. Get you a clean 5-gal bucket and dump your engine oil into it. You can tip it sideways enough to see the bottom and see that it's not instantly coated in crap. Let the bucket sit overnight and tip it again. Let the bucket sit a couple of days and tip it again. You'll probably be pretty impressed with the amount of crud that settles out of the oil. And it does not very readily come off the bottom of the bucket. If I change oil hot (5-7k, synthetic here too) I get far more crap at the bottom of the bucket than I do when changing the oil cold. The amount of oil that's inside of bearings and passages and the oil pump is pretty negligible compared to the sump volume, so allowing it to sit won't cause a lot more oil to drain out vs. leaving the plug off for five minutes while you change the filter. In fact, that oil shouldn't drain back, no matter how long it sits. What I do is drive it until hot, park it and pull the drain plug. Then do something else while it cools down a little. Usually 20 minutes to make it comfortable. Ford put my filter literally within and inch of the exhaust manifold, so touching that hot hurts. I spend that time doing other PM stuff, like checking tire pressures, cleaning out the cab, etc. Then change the filter, add oil, and fire it up. I also add some diesel fuel to my oil the day before changing it to help scrub the innards. Last time I had the valve covers off I didn't even have much varnish. SignatureB.B. --I am not a goat! thegoat4 at airmail dot net >If you run an engine to its maximum temperature and let it sit overnight >for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an >immediate hot oil change and letting it drain for the usual 10 to 30 >minutes? Some people say they wait much longer but I don't find it >practical. I agree... and the most important part is to have run the engine to its full operating temperature before draining the oil (without restarting the engine). The other way is to leave the engine cool for an hour or so before removing the drain plug and get the best of the both methods, as well as reducing the risk of being scalded. Worst thing you can for your engine IMHO is to only run it long enough to get the oil warm prior to draining it (as many do). Some even recommend you do it that way. :) SignatureJohn H > P.S. The ideal method would be to drain the engine AND pan overnight > after the engine is hot, but that takes planning and isn't always > practical. With any method, opening the oil cap to break suction should > help it flow better. FWIW, all I've ever felt is necessary is to drain the oil, take 5 minutes and inspect the undercarriage, put the plug in, change the filter, prefilling it if possible, and add fresh oil. I figure the .05 quart of dirty oil left behind isn't that big of a deal since it's only been 3-5 months since the last change anyway. I can't be bothered to wait 45 minutes or 6 hours to wait for 100% of the oil to drain - 99.5% of it is fine. I also don't worry about the temperature. Ray > > P.S. The ideal method would be to drain the engine AND pan overnight > > after the engine is hot, but that takes planning and isn't always [quoted text clipped - 12 lines] > > Ray I felt the same way until I changed the oil on a 4640 John Deere and got an extra gallon out of it by leaving it drain overnight. Six gallon bucket was four inches down on the side when I left it at sundown and almost overflowing in the morning. If I get any of that action from an auto it's worth doing - I still don't worry about the temp though. >>>P.S. The ideal method would be to drain the engine AND pan overnight >>>after the engine is hot, but that takes planning and isn't always [quoted text clipped - 19 lines] > action from an auto it's worth doing - I still don't worry about the > temp though. The only passenger car that I know of that mentions extended drain intervals is the newer Vettes - they have baffles in the pan and take ~10 minutes to get all the oil out. Otherwise, I've found that if the car holds 5 quarts of oil, if you add 5 quarts and fill the filter, you're good to go, so there's no 1/2 quart of dirty oil still in the motor. Ray > If you run an engine to its maximum temperature and let it sit overnight > for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an > immediate hot oil change and letting it drain for the usual 10 to 30 > minutes? Some people say they wait much longer but I don't find it > practical. Don't make a mountain out of a mole-hill. Either way will get MOST of the old oil out. Personally, I prefer to change the oil within one hour of a hot shut-down. When I pour the hot oil out of my catch-pan and into jugs for recycling, I notice that hot oil really does leave a lot less film on the catch-pan than room-temperature oil does, so it must also leave a lot less film on the inside of the engine oil pan. And yes, that's with SYNTHETIC oil. > P.S. The ideal method would be to drain the engine AND pan overnight > after the engine is hot, but that takes planning and isn't always > practical. And is ridiculous overkill. 90% of the oil distributed through the engine drains back to the pan within the first 2 minutes after shut-down (which is why 2 minutes is generally accepted as long enough to wait to get a valid dipstick reading). Waiting 10 to 30 minutes is, within the limits of practicality, as good as waiting overnight. With any method, opening the oil cap to break suction should > help it flow better. The engine isn't sealed so opening the oil cap doesn't do anything. It can pull plenty of air in through the PCV make-up air breather. > If you run an engine to its maximum temperature and let it sit overnight > for 10 to 15 hours, won't a lot more oil drain into the pan vs. doing an [quoted text clipped - 36 lines] > practical. With any method, opening the oil cap to break suction should > help it flow better. I've come to look at it the other way; get the thing running again ASAP while there is at least some oil that hasn't drained to keep it from eating itself during the time it takes to refill the oil filter and passages. > I've come to look at it the other way; get the thing running again > ASAP while there is at least some oil that hasn't drained to keep it > from eating itself during the time it takes to refill the oil filter > and passages. And if you really think that through to it's logical conclusion, an argument could be made that changing the filter only on every other oil change as recommended on many applications would reduce the chance of even a momentary dry start even more. In addition, a used filter, as long as it is not clogged to the point to where the bypass opens excessively, probably filters better than a brand new clean one. Lee Richardson > > I've come to look at it the other way; get the thing running again > > ASAP while there is at least some oil that hasn't drained to keep it [quoted text clipped - 9 lines] > > Lee Richardson I miss the days when you could fill up the filter and hold it vertically while you screwed it onto the bottom of the block. > I miss the days when you could fill up the filter and hold it > vertically while you screwed it onto the bottom of the block. Then you're driving the wrong types of cars. ;) Seriously, the only car I own that I can't prefill the filter on is my 4wd truck - the filter is sideways. Ray |
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