I sent the following to my nephew, the auto mechanic:

Saw an article that said idling your car to warm up your engine gently is a superstition left over from the days of carburetors. Says it’s actually less wear on your engine to just get in your car and go when it’s cold.

Your opinion?

And he gave his opinion. I’m posting it here, with his permission, to settle – or possibly start – a lot of bickering on the internet over this issue:

I mostly agree with the article. The only time I let my cars warm up now is if they are actually carbureted or if I just don’t want to deal with the cold interior.

My opinion:

For fuel injected vehicles, the extra idle time ends up being more hours of run time. All industrial engines use hours of operation to determine service intervals. Cars aren’t that much different. The biggest difference is that a car engine has to perform well over a very wide RPM range while an industrial engine only has to perform well in a very narrow RPM range. Either way, time running & all the parts rubbing up against each other is what causes long term wear. The computer easily handles tailoring the fuel mixture for actual engine temperature & incoming air temperature so excess gasoline isn’t a problem. This is why high mileage cars generally don’t scare me… You can get a vehicle that was driven by grandma exclusively around town or one that was used by a long distance commuter. The hours of operation on the 2 engines are probably very similar but with potentially a 3:1 or 4:1 difference in miles. The long distance commuter’s car actually has an advantage here because it probably has fewer starts and the transmission has shifted fewer times. Just like the clutch on a manual transmission, every time the car shifts gears the friction plates in an automatic transmission wear a little. Also, starting the car is about the worst case scenario for an engine… There is no pressurized oil keeping the moving parts from making actual contact while the starter is cranking.

For carbureted vehicles, warming up is a more a matter of safety for me. Because it is a purely mechanical system, there is no way effectively tailor the fuel mixture for ambient conditions. They can get close, but not great. In order to guarantee that the engine runs properly when starting cold, the choke linkage keeps the throttle partway open until either the operator adjusts it (manual choke) or the choke has warmed up sufficiently (automatic choke). Driving around with the choke (either type) even partially engaged for proper engine operation makes the engine run at a higher RPM. This is the equivalent of driving your fuel injected vehicle around with the gas pedal depressed 5-10% at all times even when attempting to stop the vehicle. Not a good mix for safe stopping distances. There is also the problem of excess fuel. On any engine, they will tolerate a mild excess of fuel way better than a mild excess of air. Carburetors tend to run on the rich side when everything is cold and while the fuel does vaporize, it does not vaporize well at lower temperatures. Because of the proximity of a fuel injector to the intake valve, a the gas being squirted into a fuel injected engine does not have time to re-condense before entering the combustion chamber and being burned. On a carbureted engine, the vaporized fuel has to travel all the way through the intake manifold and the cold temperatures tend to re-condense the gasoline. This can lead to raw liquid gasoline entering the combustion chamber which, as the article states, washes down the cylinder walls and removes protective oils from the surfaces.

If you want low hours of operation and a pleasant interior temperature faster, install a block heater on your fuel injected vehicle