What could happen if someone doesn’t let an engine warm up?
In: Engineering
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 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.*
I don’t even own a sweater where I live. I still let my car warm up though.
Glad to know this is completely unnecessary.
There are a few reasons.
When metal heats up, it expands. The pistons in an engine can heat up rapidly under heavy load, so much so that they may heat faster than the cylinder walls.
If that happens, the piston will expand faster than the cylinder and damage/scoring can occur.
If the engine is warmed up gradually to operating temperature, then the components will expand more uniformly.
Another reason is oil being much thicker when it’s cold. Cold oil is harder to pump into all of the small passages throughout an engine, so if you put an engine under high load with cold/thick oil, you risk damaging the bearings and other parts that need oil to survive.
A lot of people are mentioning fluids and air-fuel ratios, but I think the other issue is also the metal that makes up a lot of the engine parts that need to warm up.
Taking cold metal and applying a sudden increase in temperature and pressure to it could potentially lead to catastrophic (and premature) failure of those parts.
I warm mine up unattended for 3-5 mins, mostly so I am less cold when driving. I live in Minnesota so you can imagine the cold.
OK but which of these answers are relevant to me, a resident of the Canadian prairie winter hellscape, which gets down to -40° ?
Are the answers still generally relevant or are there additional considerations at that temperature?
Most people actually do this not to warm up the engine to prevent engine damage, but to warm up the engine so your heater is working. Nothing worse than driving in an ice cold car waiting for the heater to actually send warm air through the vents, and meanwhile your windshield is frosted over because the air trying to defrost the windshield is fricken cold. This is why Canadian cars still have block heaters. Your engine is fine, but your butt is icy.
I have been told by many mechanics that about 10-20 seconds before putting it into gear.
Reasoning is to let the oil/tans fluid to cover the parts.
Less guessing and more facts people.
Warm up is crucial for engine longevity. Pistons made of aluminum absorb heat and change size faster than your iron block. Cold start and quick high load makes the piston contact the cylinder wall causing wear.
Two stroke Detroit diesel engines used cast iron pistons and blocks so they would expand at the same rate. Thus making them superb for emergency vehicles (fire trucks) that need to go balls out as soon as they are started without compromising longevity.
And this isn’t just a winter thing. A 105° August day is not up to operating temperature for the internals for engines.
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