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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / March 2006Changed Oil, Now Oil Light Coming on at Idle. 96 Sentra.
Hi, I just changed the oil and filter on my gf's 96 Nissan Sentra (170,000 miles) and now the oil light comes on after the engine is warmed up, when the car is in Drive, and stopped, such as at red lights. After 300 miles of this, I put a different brand of filter on, but the problem remained. After 200 miles with the different filter, I changed the oil again (not filter), and the problem remained. Maybe the crank bearings are just too worn, causing the low oil pressure , and it's just a coincidence it happened right after the oil change, but I'm hoping the cause is sludge. I kept the original oil filter, and looked inside. Inside, I could see a layer of dark gray slime (sludge?) about the consistency of the grease you pump into a ball joint, laid down on the bottom of the filter ! The filter is mounted horizontally, so the slime was going from front to back, about a 1/8 to ¼ inch deep ! This sludge was in the post-filtration portion of the filter, the long channel down the center. It wasn't high enough to block oil flow back into the feed tube though. The oil light was not coming on before the oil change, even with all this sludge. But now it is. I've been changing the oil and filter every 5K to 6K on her car, but I had to leave the old oil filter on the previous time, since it refused to come off and I decided to deal with it later, so I just changed the oil and not the filter back then, so this sludged up filter had about 10K to 12K on it when I removed it. I would think other parts of the engine have sludge too, like the bottom of the oil pan where the oil pickup is. By looking into the oil filler hole, I can't see any sludge on the head. Looks very clean. There's nowhere for the oil to pool in there, at least from what I can see. Maybe the sludge is only forming where the oil can pool. I read somewhere that sludge around the oil pickup screen can cause the symptoms her car has. When I drained the oil, no sludge oozed out, just normal oil. And I changed the oil hot. Dropping the oil pan looks like a major ordeal on this car: exhaust pipe and support beam in the way. I had an idea for desludging any possible sludge on the pickup. I could heat up a quart of transmission fluid , drain the crankcase, put the drain plug back in, then pour the hot ATF into the engine, let it settle down around the pickup screen, and let it soak for a day or two, then drain it out, examine what's in it, then pour a quart of fresh oil in to flush out whatever else is there. Sound OK ? Any other suggestions welcome ! Thanks Correction ! : the sludge is JET BLACK, not gray. It looked gray when I shone a light into the filter, but when I scooped some out and wiped it on a white sheet of paper, it is clearly BLACK . Sorry for the misinformation! > Correction ! : the sludge is JET BLACK, not gray. It looked > gray when I shone a light into the filter, but when I scooped some out > and wiped it on a white sheet of paper, it is clearly BLACK . Sorry > for the misinformation! You don't mention what weight of oil you are using in the car. At 170k miles you could probably put some thicker stuff in it, especially if you live in a moderate or warm climate. It sounds like your GF's car has excessive bearing clearance and could use a rebuild. The oil filter that was left on for so long was almost certainly in "bypass" and not filtering at all. With the new filter on there (and filtering) the motor has less oil pressure than when old plugged filter was operating in "bypass". Check the oil pressure with a mechanical gage to rule out a bad oil pressure sending unit or faulty wiring. The time that the motor spent running with a plugged filter was probably pretty hard on the bearings. A motor with worn bearings can run a long time if you keep up the fluid levels and maintain it regularly. An anecdotal story: I had a '86 Ford pickup that was equipped with the 5 liter (302). The truck was a $200 beater and had over 300k on the original motor when I bought it. The oil pressure light would light up when the motor was hot and idling in drive. I checked it with a mechanical gage and it was at about 5 psi at idle when hot. I changed the oil to 20w50 and the light quit coming on at idle when hot, rechecked it with my gage and it was at about 9 psi (This time I "installed" the gage so I could keep an eye on it). The oil pressure was always over 20 psi when the motor was running at speeds over 1500 rpm. I ran this truck for another 100k miles with regular maintenance, low oil pressure at idle and all. It was tired, I knew it and I drove it with care. I sold it to a fellow that I knew with a roofing business and this truck ran another 50k miles on that motor before transmission failure took it off the road. Neglect will kill a vehicle much faster than normal wear. > I read somewhere that sludge around the oil pickup screen can cause the > symptoms her car has. This is true. > Dropping the oil pan looks like a major ordeal on this car: exhaust > pipe and support beam in the way. It's quite a minor ordeal, actually. The powertrain hanger mounts will hold the engine and transaxle in place with the longitudinal beam off, assuming the beam actually needs to be removed. I'm not so sure it does. > I had an idea for desludging any > possible sludge on the pickup. I could heat up a quart of transmission [quoted text clipped - 3 lines] > in it, then pour a quart of fresh oil in to flush out whatever else is > there. Sound OK ? Good luck with that... > Any other suggestions welcome ! Remove the oil pan and desludge the pickup screen. Feel extremely lucky if oil pressure returns to normal and the engine lasts for any significant time without an overhaul. Then perhaps change the oil and filter more often. I know, $100 a year to keep an engine running is just ludicrous; $40/year to DIY is insane. Toyota MDT in MO DO NOT TRY TO DESLUDGE IT THAT WAY. All you will do is loosen up all that 140k worth of dirt and grime and destroy your engine further. All the other advise you got is good. The oil filter running in bypass mode probably opened the bearings enough to drop the pressure enough to cause the light. What weight oil? After checking the pressure switch is good you may have to go up a grade or two in oil. Also you should start changing it and the filter at no more than 3k miles as the rings are probably loose also and the oil will get contaminated much quicker. Hi, I just changed the oil and filter on my gf's 96 Nissan Sentra (170,000 miles) and now the oil light comes on after the engine is warmed up, when the car is in Drive, and stopped, such as at red lights. After 300 miles of this, I put a different brand of filter on, but the problem remained. After 200 miles with the different filter, I changed the oil again (not filter), and the problem remained. Maybe the crank bearings are just too worn, causing the low oil pressure , and it's just a coincidence it happened right after the oil change, but I'm hoping the cause is sludge. I kept the original oil filter, and looked inside. Inside, I could see a layer of dark gray slime (sludge?) about the consistency of the grease you pump into a ball joint, laid down on the bottom of the filter ! The filter is mounted horizontally, so the slime was going from front to back, about a 1/8 to ¼ inch deep ! This sludge was in the post-filtration portion of the filter, the long channel down the center. It wasn't high enough to block oil flow back into the feed tube though. The oil light was not coming on before the oil change, even with all this sludge. But now it is. I've been changing the oil and filter every 5K to 6K on her car, but I had to leave the old oil filter on the previous time, since it refused to come off and I decided to deal with it later, so I just changed the oil and not the filter back then, so this sludged up filter had about 10K to 12K on it when I removed it. I would think other parts of the engine have sludge too, like the bottom of the oil pan where the oil pickup is. By looking into the oil filler hole, I can't see any sludge on the head. Looks very clean. There's nowhere for the oil to pool in there, at least from what I can see. Maybe the sludge is only forming where the oil can pool. I read somewhere that sludge around the oil pickup screen can cause the symptoms her car has. When I drained the oil, no sludge oozed out, just normal oil. And I changed the oil hot. Dropping the oil pan looks like a major ordeal on this car: exhaust pipe and support beam in the way. I had an idea for desludging any possible sludge on the pickup. I could heat up a quart of transmission fluid , drain the crankcase, put the drain plug back in, then pour the hot ATF into the engine, let it settle down around the pickup screen, and let it soak for a day or two, then drain it out, examine what's in it, then pour a quart of fresh oil in to flush out whatever else is there. Sound OK ? Any other suggestions welcome ! Thanks . . ======= ======= > Hi, > [quoted text clipped - 50 lines] > > Thanks ========== ========== Any...???......suggestions..?? okee dokee..... here goes..... Drain all the oil back out..... refill it with 3 qts gear oil.... top it off with the used motor oil you just drained out. post the results. this is a test...only a test if you're too lazy to test.... then disregard the reply... don't bother with a repost..... don't waste my hyperspace time..... ~:~ MarshMonster ~sips his mushroom tea.....and waits for the test results~ Out of curiosity, what type oil have you been using in this car? (It is my opinion, for which I have no proof other than my own observations, that some oils tend to sludge and varnish more than others.) In the past, I have used kerosene or Varsol to wash out engines which are badly sludged, or which have a water/oil emulsion (caused by head gaskets, etc). I have never hurt an engine this way. But, you really dont know what condition your engine is really in. These solvents are aliphatic hydrocarbons for the most part, which helps insure they dont swell or damage elastomeric (synthetic rubber) seals. DONT use paint thinner, xylene, gasoline etc. (1) You simply drain all the oil, and replace the drain plug. (2)Add 1-2 gallons of kerosene to the engine and let it stand for a day or two. (3) Remove the drain plug and drain. At this point, you can pour more kerosene through the oil fill tube until the drainage runs clear. This will help carry sludge right out the drain hole. Let all the kerosene drain out totally. (4) Add fresh oil and fresh filter and run it a couple of days. (You could substitute a 8 oz of Mystery Marvel Oil, as per directions, for part of the oil during this period. It pretty good about cleaning up varnish) (5) Then change to fresh good oil and a good filter. This usually cleans up the engines pretty well. Doesn't guarantee you will get your oil pressure back. I am a firm believer in keeping oil and filter changed regularly. It is cheap insurance. The Toyota dealership recently told me that they recommend more frequent oil changes than the owners manual may claim as a defense against the sludging problem that has ruined some engines. > Hi, > > I just changed the oil and filter on my gf's 96 Nissan Sentra > (170,000 miles) and now the oil light comes on after the engine is > warmed up, when the car is in Drive, and stopped, such as at red > lights. My friend's celebrity started doing the same thing around the 170,000 mile mark. (warm, drive, oil light flickering.) He made it another 30,000 miles before it started knocking. My $.02... I would just switch to 10w30 or 15w40 and see if the light goes out. Then keep changing the oil and filter every three months, and you'll probably get another 25k from the engine before it starts knocking. I'd consider changing the oil pressure sending unit - or at least swapping in a gauge to see what kind of oil pressure you have. If you can have 10psi per 1000 rpm with 15w40 you're probably ok for a while. Unfortunately, the only way you'd REALLY know is to pull the pan, inspect the pickup and oil pump and measure bearing clearances. The question then becomes -> what if it needs new bearings? Are you prepared to spend the money? (fwiw, we pulled the pan on the celebrity after the intake gasket started leaking coolant into the oil and had to clean the sludge out. We pulled the heads and one main cap - bearings were about at the limit, and this was about the 160,000 mile mark. Car was well maintained for the years I knew, but that's just high miles for some engines.) Ray >Any other suggestions welcome ! It's possible the oil pressure sending unit is shot. You might try replacing that before any major engine surgery. FWIW YMMV Thanks for the replies. To answer some questions… I’ve been using inexpensive oil, usually the walmart brand, sometimes Exxon, or whatever is inexpensive. Since the SAE rating on the bottle is SF, SG, SH, etc, it’s good enough for me. Since I change the oil and filter more often than the manufacturer’s rec, which is 7,500 miles, I thought I was being conscientious. I change it usually after 4K, sometimes let it go to 7K. The weight I use is 10W 30 all year. I plan to mix in some old 20W-50 Castroil which I have lying around, to see if it helps the pressure. I will try replacing the oil sending unit. I may have bumped it when getting the oil filter off. I suspect that coolant may have been leaking into the oil for a few months. The car had been using oil at about a quart every 2K, then stopped using oil. It was also using a lot of antifreeze, as in one pint every 1 or 2 days ! I had a pressure test done and they found nothing wrong. No leaks. But the antifreeze was going somewhere. But there was no vanilla slime in the oil, not even in the bottom of the oil filler cap. The mechs said the oil looked normal. They were stumped about the coolant loss. I eventually put a sealer into the coolant, and the loss is down to one pint per week now. And the engine is now back to using a quart of oil every 2 K miles also ! Looks like the coolant was leaking into the oil, and somehow keeping the oil level at the full mark, while most of it was perhaps boiling off during driving?? Meanwhile building up sludge? But no sludge in the head! I think most of the lost coolant must have been going out the tailpipe via intake manifold gasket, as well as leaking into the oil. I may try the kerosene method. Or perhaps be less aggressive first, and just add some Marvel Mystery oil for the last 200 miles before the next oil change. I’ve been severely castigated on the internet about using any sort of solvent in the engine. But, I have used Marvel Mystery oil in other cars, to clean out sludge and free up lifters with good results. I really don’t know if I have sludge in the oil pickup. The only sludge I’ve noticed was in the filter. The head looks totally clean. Maybe all that coolant boiling off and steam cleaning it ? ha ha.. I don’t plan to recommend to the gf (it’s her car) to have any major work done it the engine, since it is old and high mileage. It’s been noisy for about a year now, making clacking sounds, and slowly getting worse. Some days it is noisier than others. Some days it is actually pretty quiet. Thanks for all the info. Thanks for the story about the Celebrity. Sounds pretty similar. |
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