does warming up the the car damage the engine?

A&Q about 350Z

I'm looking for some concrete answers with some technical details thrown in. does idling the car upon startup (especially in cold weather) damage or cause excessive wear to the engine? i'm referring to gasoline engines.

i know it will release far more pollutants and use more fuel, but does it cause wear/damage, and why?


In general, running them cold doesn't damage them, but consider this.

Engines are designed to have a proper set of operating tolerances when they're hot since that's where they spend most of their time. If you start up a cold engine and run it hard, you are doing two things that aren't really smart; 1) stressing the engine while those tolerances are still at cold spec, and 2) heating certain parts faster than others. Hitting the gas in a cold engine will heat the pistons, chambers, and valves very quickly while the cylinders are still cold. Its like heating up a steel plate with a torch in the center. Its bound to warp, but if you put it in an oven and heat it all together, its easier on the steel.

On the other hand, allowing it to idle until its warm isn't always the best either. Certain parts will never heat up by just idling. It depends on the engine and its design parameters, but I can let my LT1 idle all morning and put my hand on the oil pan and it will feel cool. Since oil relies on high temperatures to evaporate impurities (in this case, mostly water) it will be operating while unadulteradely sucking up bad stuff.

Otherwise, mechanically there is very little wear that happens at idle: with the exception of cam wear. The cam relies on splash lubing from the crank. Many foreign inline engines don't anymore since they are mostly OHC. They rely on actual oil supply which they get over the entire range. But, pushrod engines need the splashed oil.

Other things will be accelerated in their wear, like Catalytic converters, exhaust, and other emission equipment won't get up to temperture and the damp exhaust will let them sit wet for a while. The O2 sensors (although not stressed by the cooler running) in some cars would never go to closed loop operation since the cats wouldn't heat up enough to light off. EGR valves will often rust internally in cars that don't have a lot of "highway" miles.

This is all extreme generalization. I have a BMW e30 with a 2.5L I6 that gets fully hot very quickly, but maintains that temp regardless of idling, heavy traffic, canyon carving, or sunday driving. The oil temp will be a little cooler on the sunday drive, but when you compare that to my LT1 that probably never tops 120 degrees oil temp if left to idle, its a big difference. My wife's Tercel will overheat at idle if left unchecked, so it entirely depends on engine design.

I think the best compromise is to start it, give it a second for the idle to stabilize, then drive gently until its warm. You won't optimize things like thermal stability, but you will optimize things like even heating and cam wear.

excellent analysis by curtis, once again.
Just a couple of more things.
1. Warming up an engine before driving is mostly a hold-over from the days of carburetion. Carb engines require a heated intake manifold and intake passages to function at their best, because the atomised fuel is more likely to fall out of suspension when the engine is cold, causing inefficient combustion and drivability problems.
Fuel injected cars mostly are free of this limitation, so they run better when cold; and are more satisfactory to drive at cold engine temps.
2. Warm engines wear less. Oil and coolant temperatures below approx. 180 degrees F cause accelerated engine wear (According to Navistar (International Harvester) engineers). Therefore, theoretically, one can expect greater engine wear, if engine stresses are higher (like when you drive, instead of idling) when the engine is cold.
However, idling warms the engine slower, thus exposing the engine to a longer duration of high wear rates at cold temps.
As curtis says, the best solution is to let the engine idle for about 10 seconds, to allow for full oil pressure to arrive, then drive modestly until the engine warms up.

Some of that is good stuff, but fuel injected engines still do need to warm up, especially in colder weather. If you have ever started your engine up on a cold morning and noticed that it is idleing a little bit fast this is because your computer knows that your engine isn't warm, once the computer sees that the engine is warmed up, it will drop the rpm's back down to the normal operating level and also lean the fuel back to normal. Though this doesn't matter much on vehicles that are driven on longer trips it does matter for cars driven on short trip intervals, like grandma that just drives down the street to the grocery store.

So honestly i would say let it warm up till the revs drop.

As far as engines running better when they are cold, you have to anylize what you are saying.
Colder air temps - yes
colder engine, oil, coolent temps - no

Actualy, rotaries (especially carburated rotaries) you are sapposed to hold at 3,000-4,000RPM for 9 seconds after start up in normal weather. but there are many websites and rotary enthusyasts that say its easyer on the apex seals if you hold it at 3k for 4sec and then hit 9,000 and drop the throttle. but thats what i heard.
this is done to prevent flooding. if a friend ever gets a carburated RX-7 (or any roatary) make sure that if you move it for him to make sure the engine is nice and warm before shutting if off or the engien will flood and depending on how bad may be a pain to get it to start agian.

just thouhg i would add that in baout warming enignes up.
but as Curtis73 said, reving it on start up in cold weather will heat vualves and all but not the block and heads which will make pistons nad vualves etc expand but not their encasisng causing warp or excessive wear.

This cold start fast idle is programmed in ONLY to reduce cold start emissions. It gets the catalytic converter heated up sooner which allows it to clean up the exhaust earlier.
Auto manufacturers have to meet cold start emissions standards; hence this fast idle is required. Personally, I suspect that a unnecessarily fast idle when cold can only accelerate wear on the engine itself.

Interesting that nobody mentioned that gasoline will wash oil from the cylinder walls in the excessively rich environment of a cold engine, so in one way it is best to get the motor warmed up as fast as possible. Just thought I would bring up a counter point, not trying to discredit any of the very good ones brought up here.

As for rotaries, I own one and typically it floods the worst when it has been sitting for about a week or more. Don't get me wrong though, the only times I have had it flood where when it was out of service for a long time for maintainance. Once it floods it can take up to an hour to get it running again, because you have to remove the plugs, dry them, ground the coil, crank the engine over a few times to clear the housings of fuel, then reinstall and try to start it again. Typically this will not work the first try and will require three or four tries to finally start the car. Rotary engines do not unflood by themselves which, to put it simply, sucks.

Magic rat, you said that an unecesarrily fast idle will when cold will accelerate wear on an engine which was my point exactly. If a higher cold idle (no load) is increases wear, imagine what driving (higher load) will do to engine before it is warmed up. That is why i was saying just let the engine warm up on its own.

These are all good points, but we keep dancing around the full story. On carbureted engines, idling them until they're warm is a convenience to drivability. It is true that the exessively rich (sometimes 5:1) mixtures will wash down cylinder walls, but keep in mind that at no load idle (especially fast idle) places almost NO load on the cylinder walls. There is little combustion chamber pressure forcing ring seal, so the wear in neglegible. What DOES kill these carbed engines is the excessive oil dilution from the poor ring seal and washed walls letting excessive gasoline into the oil. This was the original cause for concern on vehicles that were used for short distances, and the proliferation of the sales pitch, "highway miles." On short trip cars, the oil continually stayed diluted, but on highway cars, the oil reached temps that evaporated the junk out of the oil. The reason for the excessively rich mixtures, as we all know, was that the cold walls of the intake condensed the fuel making sheets of fuel break off and get sucked in. The high idle was to counteract the volatile nature of the mixture. Driving a carbureted car before it was warm did two things that sucked; 1) The excessively rich mixture washing down the walls, plus the load placed on the engine meant you had optimum ring-to-wall pressure, without the oil present to prevent cylinder wear. 2) Operating the accelerator pedal meant operating the accelerator pump, further exaggerating the rich mixture.

On today's EFI cars, the cold mixture is still rich, but more on the order of 11-12:1. The fine atomization and nearly direct injection of the fuel means you don't need to run them as rich on cold start. It also means that regardless of the rich mixture, it remains gaseous in the chamber instead of liquid, so the cylinder washing is all but eliminated. That parameter of cold running is effectively eliminated with EFI, so it comes down to the other aspects we've discussed here.

Im my little opinion, if you have a carbed engine, the best way (other than an electrically heated block) is to start it and keep it on fast idle until its ready to "kick down", then drive it. That means it spends its "cylinder washing" time at no load, then spends the rest of its time burning off the contaminants from the oil... provided it runs long enough to get the oil up to temp. If you have an EFI engine, I suggest starting, waiting a few seconds until everything stabilizes, then driving gently until it warms up. This minimizes localized heating of parts and the abnormal wear that potentially occurs with it. There is neither a benefit nor a drawback (other than using fuel and contributing to pollution) to letting an EFI car idle until it warms up.

There are other things involved, like oil temps. Oils are designed to satisfy engine's needs at cold temps, but be optimal at operating temps since that's where most engines spend their time. Driving an engine under load brings the oil up to temp much faster than at idle... where it may never reach proper temperature. Another factor is that some engine designs (as examples, mopar, buick, and pontiac) are very poor at oiling the top end at idle. Valves and rockers may starve for oil if the engine is allowed to idle for long.

I think its somewhat a moot point once we get this specific. On average, no one complains that their Dodge 440 died of valve failure because they idled it too long, and no one complains of cylinder wear on their Olds 330 because they flogged it when cold. I think its a matter of a few thousand miles of engine life either way you look at it.

Ideally, I think the best way to maximize the situation is to use EFI, an oil heater, and a pre-lubing pump. That way you have minimal cylinder washing, pre-lubed bearings, and warm oil to start with.

The best way is of course to always use a heater for the engine. Doing that will reduce wear and the engine will usually run well directly from the start. With racing engines a heater can be required, a cold start can damge such an engine that it later can fail.

Typically it's best to start the engine, let it idle for a short while so it can build up oil pressure and then drive it without high loads and engine speeds. When the oil temperature has climbed up to 70 degC or so you can start to use higher loads and speeds.

Another engine type that gets into trouble with cold weather is the diesels which need the combustion heat to ignite the fuel. Using start gas which contains ether can also result in an uncontrolled combustion which can crack the piston rings.

Ether can also damage glow plugs.
Some diesel engines that I have had which use pre-combustion chambers in place of glow plugs have an ether injection system factory-installed for cold weather starts.

Sorry to dredge up an old thread but I though I would add my 2 cents as I live in a very cold country and my cars go through brutaly cold starts all winter long. I agree that extended warmups are probably a leftover habit from the days of carbureted engines. Per various owners manuals and my own anecdotal observations more than about 2 minutes is a waste of gas. I usually don't wait that long. I have never noticed any damage or other ill effects from this to any of my vehicles from high compression carbed motors to late model turbo engines. Not saying it isn't theoretically possible, or that something might not show in very high mileage engines but in my city which spends all winter in a deep freeze(sometimes below minus 40)most people don't take any special warmup precautions and our cars last as long as they do in Texas or Florida.
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