 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Australian Car Forums / General Car Topics (Australian group) / June 2007Cars run rougher when cold, why is it so?
Ok cold air means more oxygen, so therefore it posibly leans off the fuel mixture in a traditional carby car, and even my brothers diesel was a dog to drive till it warmed up. So the correct choke setting makes the car run better by richening the fuel mixture. but when the motor has warmed up, what has actually changed to make the motor run better then normal if anything on the same cold dense air it ran like a dog on beforehand. Does the warm manifold actually reduce the oxygen density by pre-warming the mixture or just make it easier to ignite? Or is it related to the engine componenets being tighter till they expand when warmer? > Ok cold air means more oxygen, so therefore it posibly leans off the fuel Correct. > mixture in a traditional carby car, and even my brothers diesel was a dog to > drive till it warmed up. Even under high compression diesel won't ignight, so need glow plugs plugs or a manifold air heater. All good once it gets going (t'other weekend had to fix plugs in a Smurf where two had gone, and the colder weather was taking it's toll). All good now. > So the correct choke setting makes the car run better by richening the fuel > mixture. but when the motor has warmed up, what has actually changed to make > the motor run better then normal if anything on the same cold dense air it > ran like a dog on beforehand. You are trying to start a fire in the cold damp woods. > Does the warm manifold actually reduce the oxygen density by pre-warming the > mixture or just make it easier to ignite? You need to make the fuel closer to it's flash point.. > Or is it related to the engine componenets being tighter till they expand > when warmer? Nah, not really. They're angry.  SignatureDon't try to reply to my email addy: I'm borrowing that of the latest scammer/spammer > Ok cold air means more oxygen, so therefore it posibly leans off the fuel > mixture in a traditional carby car, and even my brothers diesel was a dog > to drive till it warmed up. Cold air = denser = means better volumetric efficiency = better performance, but only once the engine has warmed up. > So the correct choke setting makes the car run better by richening the > fuel mixture. but when the motor has warmed up, what has actually changed > to make the motor run better then normal if anything on the same cold > dense air it ran like a dog on beforehand. The cold air isn't the problem, the cold engine is. A cold combustion chamber inhibits a good clean and even burn. > Does the warm manifold actually reduce the oxygen density by pre-warming > the mixture or just make it easier to ignite? The fuel mixture is less likely to condense on a warm manifold. > Or is it related to the engine componenets being tighter till they expand > when warmer? Having the combustion chamber closer to combustion temperatures aids even and complete burning of the A/F mixture. > Ok cold air means more oxygen, so therefore it posibly leans off the fuel > mixture in a traditional carby car, and even my brothers diesel was a dog to [quoted text clipped - 9 lines] > Or is it related to the engine componenets being tighter till they expand > when warmer? Its all about atom's and the atmospherics under which they atomise > Ok cold air means more oxygen, so therefore it posibly leans off the fuel > mixture in a traditional carby car, and even my brothers diesel was a dog to [quoted text clipped - 9 lines] > Or is it related to the engine componenets being tighter till they expand > when warmer? When the engine is cold, you need to add more fuel to compensate for the fuel that condenses on the walls of the cold combustion chamber and doesn't contribute to combustion. It's a bit like your windows on a humid morning. Hence using the choke for a carburettor, or some other means of enrichment if you have fuel injection. This is not an exact process, and the emphasis tends to be on providing "enough" fuel rather than the correct amount - particularly with a carburettor. therefore the engine runs a bit rough. Fuel injected cars usually warm up more gracefully because the mixture is more accurately controlled according to the actual engine temperature as it warms up. Chokes, whether manual or automatic are a guess. Diesels are different again, and have glow plugs to replace the heat lost as the fuel condenses as someone else mentioned, but you don't get good vapourisation of the fuel until the engine warms up properly. >Ok cold air means more oxygen, so therefore it posibly leans off the fuel >mixture in a traditional carby car, and even my brothers diesel was a dog to [quoted text clipped - 4 lines] >the motor run better then normal if anything on the same cold dense air it >ran like a dog on beforehand. Poor and incomplete combustion due to lousy fuel metering and atomisation is the main culprit. Causes a smelly exhaust in petrol engines and white smoke in diesels. Carburettors under choke don't meter and atomise as well as they should and neither do worn, or incorrectly set, injectors. Injected engines with healthy injectors are the least affected. Direct injected diesels fare better than those with pre-combustion chambers. Marginal HT voltage can also be a factor in petrol engines. A denser mixture has a higher resistance to the spark and the high humidity at lower ambient temperatures also causes component leakage (take a look at an engine running in the dark if you want to see the effect). Modern electronic ignition systems do much better than Kettering (in terms of a stronger spark). >Does the warm manifold actually reduce the oxygen density by pre-warming the >mixture or just make it easier to ignite? The main effect of a warm manifold (or intake air) is to evaporate the fuel droplets resulting from poor atomisation and hence improve combustion. It's otherwise counter-productive, since a warm mixture decreases volumetric efficiency. >Or is it related to the engine componenets being tighter till they expand >when warmer? Viscous drag and reduced thermodynamic efficiency, and the resulting power losses, cause reduced idling speed and stalling (which is why the idling speed is usually increased in a cold engine). Colder combustion chambers, and their surrounds, mean that more fuel energy is lost to heat. The effect is a lot greater than often realised (and the reason why modern engines use hotter thermostats than those of yore). There's also a reverse effect of temperature... some engines run quieter, and seemingly smoother, at higher ambient temperatures (especially if they're well worn or badly tuned). The lower volumetric efficiency reduces cylinder pressures and quietens the engine (much the same as retarding the spark). A snake oil device in the form of a heating coil in the air intake, which makes an appearance every few years, exploits this effect. SignatureJohn H > Injected engines with healthy injectors are the least affected. > Direct injected diesels fare better than those with pre-combustion > chambers. Possibly looking at a greater volume of cold surface metal in Indirect. injection. Yeah, they don't like it. Direct injection diesels (ie: Cummins 6BT) can get away with an air heater on the manifold, and not glow plugs. >> Injected engines with healthy injectors are the least affected. >> Direct injected diesels fare better than those with pre-combustion [quoted text clipped - 3 lines] >Indirect. >injection. Yeah, they don't like it. It's almost certainly an atomisation issue... ie the relative surface area of the fuel droplets. White smoke at startup is unburnt fuel. (Overfuelling, which results in black smoke, is a completely different issue.) >Direct injection diesels (ie: Cummins 6BT) can get away with an >air heater on the manifold, and not glow plugs. In the older Cummins engines, with their PT fuel system, white smoke at startup on a frosty morning was usually a sign that the injectors needed setting. Most direct injection diesels will start and run fine without any assistance at close to 0°C or so (I've not had any experience with diesels at lower temps). For large industrial diesels ether has long been the standard low temperature starting aid but I'm yet to see one that had it fitted (most have provision for an optional starting aid from new). I'm guessing that they sell very few of 'em in Oz. Come to think of it... the diesel I've most recently acquired (got it at an auction a few weeks back and haven't yet made time to play with it) is an Iveco. It's got provision for an intake heater but there's not one fitted... might even get up early and see if it starts come the next frosty morning. Glow plugs are for Jap crap. :) SignatureJohn H > Come to think of it... the diesel I've most recently acquired (got it > at an auction a few weeks back and haven't yet made time to play with [quoted text clipped - 3 lines] > > Glow plugs are for Jap crap. :) I've seen some early cummins diesels NTC and K19's with a switchable glow plug system fitted. I know some large diesel engines were a c.nt to start in cold temperatures. I remember starting up and old Kenworth with a Cat 3408 and it was a c.nt of a thing to start. When it did start it spluttered and farted and shook it was like it was having a stroke (no pun intended). But as usual when it was warm it fired up first pop. SignatureRegards Dan >I've seen some early cummins diesels NTC and K19's with a switchable glow >plug system fitted. I know some large diesel engines were a c.nt to start >in cold temperatures. I remember starting up and old Kenworth with a Cat >3408 and it was a c.nt of a thing to start. When it did start it >spluttered and farted and shook it was like it was having a stroke (no pun >intended). But as usual when it was warm it fired up first pop. No Cummins or Cat I've owned (Cummins 855NTA & M11, Cat 3406 & 3208) has ever had any sort of cold start aid (apart from the 110 volt block heaters fitted for the North American market). Until the introduction of low sulphur, minimum starting temperature was always determined by the gel point of the fuel. Nowadays (low sulphur, low wax) it doesn't get cold enough to stop any direct injection diesel in good condition from starting (-3°C is about as low as it gets where I am, and never for long so engines probably don't get nearly that cold). Which isn't to say some wouldn't have smoked a bit at startup, though I'm inclined to give any that do a sniff of ether (Aerostart) whenever it's really cold. It's an old habit from the days when we had a crank start Southern Cross diesel on our house genset (didn't have mains power until 1985). It's no great hastle to squirt a bit into the air intake of a truck, or anything else, prior to the first start of the day. :) SignatureJohn H > No Cummins or Cat I've owned (Cummins 855NTA & M11, Cat 3406 & 3208) > has ever had any sort of cold start aid (apart from the 110 volt block [quoted text clipped - 4 lines] > from starting (-3°C is about as low as it gets where I am, and never > for long so engines probably don't get nearly that cold). I guess it was an option because I remember seeing a rocker switch on the dashboard on a truck saying glow plug on and off. I guess the driver flicks it on for a few seconds to a minute maybe and flicks it off and then starts it. > Which isn't to say some wouldn't have smoked a bit at startup, though > I'm inclined to give any that do a sniff of ether (Aerostart) whenever > it's really cold. It's an old habit from the days when we had a crank > start Southern Cross diesel on our house genset (didn't have mains > power until 1985). sh.t middle of nowhere huh? :-) > It's no great hastle to squirt a bit into the air intake of a truck, > or anything else, prior to the first start of the day. :) You just liked the smell of the stuff didn't you! ;-) SignatureRegards Dan >> It's no great hastle to squirt a bit into the air intake of a truck, >> or anything else, prior to the first start of the day. :) > >You just liked the smell of the stuff didn't you! ;-) It's actually sh.t awful. :) Got my first whiff at a very tender age -- used to make my own fuel for the old ED Racer (for those who remember 'em). SignatureJohn H > >I've seen some early cummins diesels NTC and K19's with a switchable glow > >plug system fitted. I know some large diesel engines were a c.nt to start [quoted text clipped - 23 lines] > -- > John H Well my Pug is a sh.t to start in the cold. I suspect its because the rotary injector pump (that old bulldozers would have) isn't as accurate and adjustable as the modern in-line injectors are. Newer 4wds don't even have a glow plug light - it heats up so fast you don't even notice. >>> Injected engines with healthy injectors are the least affected. >>> Direct injected diesels fare better than those with pre-combustion [quoted text clipped - 29 lines] > > Glow plugs are for Jap crap. :) Our house genny is a real old pokkie knocker with hand crank , wind the flywheel and drop the hammer POP POP POP POP :) well it works and makes cheap power > >>> Injected engines with healthy injectors are the least affected. > >>> Direct injected diesels fare better than those with pre-combustion [quoted text clipped - 33 lines] > flywheel and drop the hammer POP POP POP POP :) > well it works and makes cheap power Our supervisor played farming on his few acres, and water was always a problem for cattle/sheep. The place came with an old Lister petrol single cyl/pump on the dam (at lowest and farthest point on property. Had no trouble knowing if it was filling the top-tank. The exhaust "pop" was most characteristic, and revved at about 1100rpm (guess). He put a 3 1/2 hp B&S in service at one stage,..fell to pieces in a couple of weeks. So out came the Lister again, got a valve seat insert and go. Must have been at least 40 yo. Jason >Our house genny is a real old pokkie knocker with hand crank , wind the >flywheel and drop the hammer POP POP POP POP :) > well it works and makes cheap power Ours was a Southern Cross BDC. Flywheel weighed about the same as typical car engine and it ran at 800rpm IIRC. Burned around 2 litre per hour of whatever you wanted to feed it. Thankfully its crankshaft broke the year before we got mains power, so I replaced it with an ST3 (Lister) and kept the alternator (10kVA brushless Dunlite). Have it permanently wired in as a standby with a changeover switch on the main board. Bloody good thing too, coz the nearest service crew is now 160 km away. After they've been missing in the bush for a day HQ then sends a helicopter out to find 'em (as well as the fault) and the power usually comes back on the day after. Telstra are somewhat worse. SignatureJohn H > Does the warm manifold actually reduce the oxygen density by pre-warming the > mixture or just make it easier to ignite? > Or is it related to the engine componenets being tighter till they expand > when warmer? Think how humans behave when its witches tit freezing. :-) SignatureRegards Dan > > Does the warm manifold actually reduce the oxygen density by pre-warming the > > mixture or just make it easier to ignite? > > Or is it related to the engine componenets being tighter till they expand > > when warmer? > > Think how humans behave when its witches tit freezing. :-) Well, I've taken a cold shower when it was 5C. Your head/brain feels like it's about to explode washing hair.... I installed a hot water system now. In JT speak .... cold.showers.make.for.less.water.usage :-) >> > Does the warm manifold actually reduce the oxygen density by pre-warming >> > the [quoted text clipped - 12 lines] > > cold.showers.make.for.less.water.usage :-) We call it spanner water. Because it tightens the nuts. Fraser >> Think how humans behave when its witches tit freezing. :-) > > Well, I've taken a cold shower when it was 5C. Your head/brain feels > like it's about to explode washing hair.... I installed a hot water > system > now. I don't have to worry about washing my hair because I am by choice (shaved head) bald. :-) SignatureRegards Dan > Well, I've taken a cold shower when it was 5C. Your head/brain feels > like it's about to explode washing hair.... I installed a hot water [quoted text clipped - 4 lines] > > cold.showers.make.for.less.water.usage :-) Cold temperatures seem to make my pump cycle more, or maybe I notice it more. I use more water, as I dodge out of the spray when it goes cold, and go back in when it goes back to warm. Bloody annoying! SignatureDon't try to reply to my email addy: I'm borrowing that of the latest scammer/spammer >> Well, I've taken a cold shower when it was 5C. Your head/brain feels >> like it's about to explode washing hair.... I installed a hot water [quoted text clipped - 8 lines] > more. I use more water, as I dodge out of the spray when it goes cold, and > go back in when it goes back to warm. Bloody annoying! Sounds like you are on a pressure pump system like me. This is caused by the shower head restricting the water flow to much for the pump. Either get a larger shower head that lets more water flow, or get a smaller pump. I have a larger shower head and it makes the small version house pump run all the time, no more hot/cold fluctuations and I get nice and wet in the shower.All my grey water goes back out to the paddock, and it comes from the well so I have plenty of water to play with. If you want to have a larger pump for hose pressure with several taps, etc, then use a small pump for the hot water system and the cold shower tap. Longer term I'm going to add another tank up the hill from the house (2 bedroom garage!) and gravity feed to everything....just need to get a round tuit... Hope this helps, Pete >>> Well, I've taken a cold shower when it was 5C. Your head/brain feels >>> like it's about to explode washing hair.... I installed a hot water [quoted text clipped - 29 lines] > Hope this helps, > Pete It's very odd. apparently if I turned up the shower full blast, it'd make the pump go the whole time and it wouldn't cycle so badly (I have one of those standard shower heads on a long stick, seems large enough). Everything's downhill of the house, which doesn't help. but on freezing mornings, it's very unenthusiastic (I've wrapped all the pipe things at the tank and pump with wads of newspaper). It might be the distance that is causing lag, too. By the time the pump notices that more is needed, pressure's dropped right off in the shower. SignatureDon't try to reply to my email addy: I'm borrowing that of the latest scammer/spammer >>>> Well, I've taken a cold shower when it was 5C. Your head/brain feels >>>> like it's about to explode washing hair.... I installed a hot water [quoted text clipped - 37 lines] > It might be the distance that is causing lag, too. By the time the pump > notices that more is needed, pressure's dropped right off in the shower. Check the air preasure in the pump bladder >>> Does the warm manifold actually reduce the oxygen density by pre-warming the >>> mixture or just make it easier to ignite? [quoted text clipped - 10 lines] > > cold.showers.make.for.less.water.usage :-) On the farm when I kid we rarely bathed more than once of twice a week , heating copper and sorting a bath was a majpor drama so birdbaths were the go , and in subzero I guess the bacteria that make most smells seem inactive ( oy you cant smell your self) :) If all else failed the warm water used to hose the cows udders was fine for a scrub down the shed :) > Ok cold air means more oxygen, so therefore it posibly leans off the fuel > mixture in a traditional carby car, and even my brothers diesel was a dog to > drive till it warmed up. When an engine is _that_ cold, plus the heat taken out of the air from the metered in at the carb, the fuel condenses and ends up on the manifold runner and port walls, and to some extent the cylinder wall, and it won't make it into the engine as well. So you need to add more to compensate. That's the main reason believe it or not. SignatureJohn McKenzie tosspam@aol.com abuse@yahoo.com abuse@hotmail.com abuse@earthlink.com abuse@aol.com vice.president@whitehouse.gov president@whitehouse.gov sweep.day@accc.gov.au uce@ftc.gov admin@loopback abuse@iprimus.com.au If you didn't know it was wrong,why did you cover it up? abuse@msn.com $USER@$HOST $LOGNAME@localhost -h1024@localhost root@mailloop.com abuse@federalpolice.gov.au fraudinfo@psinet.com abuse@cia.gov $USER@localhost abuse@sprint.com abuse@fbi.gov abuse@asio.gov.au $LOGIN@localhost RainbowWarrior said.... > Ok cold air means more oxygen, so therefore it posibly leans off the > fuel mixture in a traditional carby car, and even my brothers diesel was > a dog to drive till it warmed up. I once had a radiator hose blow on me. Car quickly overheated. I replaced the hose, refilled it, etc. Then I noticed that it was taking forever to get to temperature. And even then the gauge wouldn't go much past the cold mark. I realised that the the thermostat was stuck wide open. But during that period the car's fuel economy improved out of sight. It was an old carby'ed 253 V8 Holden (carby was a Holley 350). It appears that the cold water in the inlet manifold was causing the dense air to help with economy, much like a cold air intake on modern vehicles (and back then Brock HDT Commodes) does these days. > RainbowWarrior said.... > [quoted text clipped - 14 lines] > air to help with economy, much like a cold air intake on modern vehicles > (and back then Brock HDT Commodes) does these days. Adding a bypass to the manifold so that it doesn't get hot is a well known performance modification. Patrick said.... > Adding a bypass to the manifold so that it doesn't get hot is a well > known performance modification. Presumably, on Holden V8s, that this would incorporate a new set of manifold gaskets to stop coolant flow through the manifold? SignatureFirst things first, but not necessarily in that order. > Patrick said.... >> Adding a bypass to the manifold so that it doesn't get hot is a well >> known performance modification. > Presumably, on Holden V8s, that this would incorporate a new set of > manifold gaskets to stop coolant flow through the manifold? The water heated early plastics dont have a water path from the gasket faces to the jacket under the carby. They have a jacket under the carb that is a stand-alone area, which is fed coolant from a port on the thermostat housing (under the thermostat) via a moulded hose to alongside the driver's side of the carby. The coolant then flows out the top of the manifold on the other side of the carby into another water hose going to the interior heater... I've done straight LPG conversions in these in the past, where we simply removed the water circuit under the carby and fed the hose straight from the theromostat housing to the heater. It's when they have exhaust crossing under the carby that the manifold needs to be lifted to block the ports. The stock chev cast iron inlet on the current engine in the Volvo has those ports welded and a small breather hole drilled into the crankcase at the middle bottom to avoid having a sealed volume... The inlet for the new engine is an Edelbrock Performer RPM Air-gap. It has no crossover port and has the (dual plane) runners lifted clear of the valley to allow air flow like the Victor Junior... SignatureAthol <http://cust.idl.com.au/athol> Linux Registered User # 254000 I'm a Libran Engineer. I don't argue, I discuss. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.