What could happen if someone doesn’t let an engine warm up?
In: Engineering
I found this…
*When an internal combustion engine sets overnight the mechanical components will be cooler than when at “ideal” operating temperature. Engine wear is most experienced at cold start due to the lack of oil available to engine components. The dimensional tolerances will be at the non-ideal design limits. Maximum clearances in all bearing and piston to wall specifications. The piston will be an oval shape having not expanded to true oval for minimal clearance. Some piston slap will cause some wear on the piston skirts until thermal expansion maximizes. No lubrication oil will be top side or on the cylinder walls. This is where the most “wear “ occurs. Metal to metal and no lubrication. Why? The oil pump galleries may be dry with no oil present. Today 99% of the cars on the road use mechanical oil pumps. This means the pump oil pump cannot deliver oil pressure until it has sucked up the oil from the oil pan sump and has begun pushing the oil through the oil galleries. From cold start until the engine warms up and the oil fills all the oil galleries and we have a steady oil pressure reading we do not have proper lubrication. It was true that we suffered a lot of cylinder / piston wear about 20 years ago. The cylinder walls used to be honed and finished with many peaks and valleys remaining in the surface profile. The introduction of Plateau Honing meant the peaks were knocked down on final hone pass so the engine break in time was a lot shorter and we had significantly more valleys to retain oil. Todays computerized fuel monitoring means we do not have excessive fuel splashing on cold cylinders at start up unlike the day of the “choke”. Your assumption that ”thicker oil” does better lubrication is not true today with the introduction of synthetic oils. Cold start lubrication is best achieved from an oil with good cold flow Properties. The reason the 98C wear is the least is the engine is functioning properly. At 20C the engine is way too cold and piston rings are permitting too much blow, washing the lubricating oil off the cylinder walls. The piston is not thermally expanding for a tight piston ring seal. When the oil is not heated to proper temperature harmful deposits, moisture, and acid accumulate rapidly, then eat away at the inside of your engine. There is a lot of chemical things happening during the combustion process so you must change engine oil at least every 3 months regardless of the miles driven. You literally have acid and sludge developing in the crankcase.*
Everyone here is pretty much spot on about not really “warming up” gasoline cars, but driving them conservatively until warm. But yeah, that does mean there is still a “warm up” period. The engines are designed to run at a specific temperature. The various parts all expand and contract at slightly different rates, and you don’t want to put sudden changes in load on it until everything is at the temp it’s designed for. But yeah, just driving it is better than not, because it heats things up faster.
I always thought warming up the car meant turning it on and getting the heater on the inside going.
I was told getting the engine up to temp will evaporate any moisture build up from sitting cold. That’s why its so rough to start and stop a engine cold. From an old GM mechanic.
It used to be the case that you’d manually adjust the AFR (air fuel ratio) of the engine when starting it with the choke during a cold day, and then let it warm up so that it could idle unsupported. when it first started, it wouldn’t be able to self-sustain without using the choke. after it was warm you could drive. nowadays a computer controls the AFR and automatically adjusts it according to tempurature.
the other part of it is oil circulation, which is something that still makes me cringe. Watching someone start an engine and immediately start driving it. The oil pump will not have sufficient pressure to lubricate the engine properly for at least a couple of seconds, as oil falls back into the sump after a short while of the engine being off.
When i start a modern vehicle, i let the engine run for at least 10 seconds before moving. Normally i just start the engine, then get my gloves and helmet on. this provides a convenient time measure, enough for oil to circulate.
In general, engines just like to be at their operating tempurature. their parts are machined to the correct tolerances for a given tempurature. for example the piston rings are set to provide a good seal at around 150-250 degrees, so when they’re dead cold, they’re slightly too small and don’t provide a good fit.
People have mentioned what is happening inside the engine, there is a practical safety concern. If you don’t warm up your car, your windshield defroster won’t work. The interior heat is waste heat from the engine. Even if you scrape frost off of the windshield, your breath can condense on a cold windshield and blind you.
You don’t have to warm your car up for very long. If the windshield is clear when you get in, it won’t fog up immediately, and your engine generates heat quickly while you’re driving. But the defroster is a safety system, it is considered bad luck to drive blind. Warm up your car so that the defroster can work.
Mainly to get the oil circulating. In cold weather, oil increases in viscosity (thickens) and after sitting at the bottom of the engine all night, it’s hard to pump up to the very top.
Multi-viscosity oil (10W-30 — 10 *Winter*, 30 Normal) help mitigate this, but just because it’s better than it was before doesn’t mean you can just ignore it.
Regardless of the weather though, the majority of the wear and tear an engine suffers is during startup because it’s not properly lubricated.
Engines also have little rubber seals and O-rings that do their jobs better when they are warm and oiled.
But on a much more practical level, the engine warms up the coolant which is where the heater gets the heat from, so a lot of people let their car warm up just so the cabin has heat.
Car manufacturers generally recommend against idling engines to warm them up, beyond letting it run for 30 seconds or so to let the oil circulate. Idling an engine to warm it up can cause extra wear because you’re prolonging the time the engine is running below operating temp. Driving it with moderate amounts of throttle and revs will warm it up more quickly.
While the engine is still cold a lot of unburnt fuel and condensation is going to make its way into the oil and exhaust system, so you don’t want to have it running in this state any longer than is necessary. There’s also the issue that while the coolant is going to heat up if you idle the engine, the engine oil takes much longer to get up to temperature if the engine isn’t doing anything.
It depends how cold we’re talking about, and what you mean by “warming up”.
If it’s so cold that the coolant in the engine freezes (or anti-freeze hasn’t been used), and it’s not been pre-warmed up, it could block up the coolant pipes causing an increase in pressure in certain areas of the cooling system, which could cause permanent damage.
Back when engines used carburetors, cold engines would need to be warmed in order to get the proper fuel-air mixture for sustained ignition/combustion.
Nowadays, however, it’s entirely unnecessary; engines have fuel injectors and sensitive instrumentation that adjusts the mixture for optimal combustion.
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