There are opinions all over the map on this one. Some say allowing the car to idle too long washes the cylinders down with the gas, causing excessive wear and it wastes gas.
Let’s look at this from a factual perspective. If it’s a given, then different metals expand and contract at different rates. The cast iron engine block sitting under the aluminum heads will actually move around slightly under heavy loads. This movement is diminished somewhat when temperatures are stabilized such as after warm up.
It is certainly more comfortable to get in a warmer vehicle with the frost off the inside and ice or snow off the outside. Am I advocating a warm up of 15 to 30 minutes? No. Maybe a 3 to 10 minute depending how cold it is.
Certainly don’t try to drive a car with a supercharger or turbo charger with cold engine oil. The tiny needle bearings turn 10 to 15,000 RPM and they like warm oil to protect them from excessive friction.
We all know a diesel engine won’t produce much power until it builds a little heat in the engine. They will rattle and make you think it will die when you press the throttle on a cold engine.
Anyone that has ever participated in any track events, automobile, truck or motorcycle racing knows to bring the engine up to operating temperature before any extreme loads are placed on the engine components. So please keep those poor cold engine bearings in mind next time you fire up your grocery getter on a 20-degree morning and rev it up. Just allow it to idle for a few minutes to build a little heat and stabilize the temperatures before standing on the throttle.
By the way, as for cylinders being washed down with gas, you are idling. The mist of fuel being put into the cylinder should be thoroughly used up through combustion. Cylinders get washed down with gas when engines are revved up and the ignition shut down. Then the excess fuel can wash a cylinder wall and if done often enough, yes you can contaminate the oil with excess fuel.
As for a reduction in gas mileage with your car idling, yes, your gas mileage will suffer slightly. Do the math with your mileage. How much does your gas cost you per mile to drive?
If you work the mileage difference you may find the extra warm up time might cost you 25 to 50 cents. But you only do this on really cold mornings. You will spend a few extra dollars per tank. Weigh the cost and make the best decision for your driving needs.
For me, I’ll warm the engine and take care of my bearings.