Is leaving your engine running good for it?

Answer 1

He is right! Running a warm engine under load uses far less fuel and causes far less wear than running a cold engine under load.

This is why fire engines and other emergency vehicles often use engine preheater systems that keep the engine coolant at operating temperature (or close to it).

Also, you will use far less fuel in your first few miles of driving. That will more than make up for the fuel used warming up the engine (provided you aren't warming the engine for hours!).

As the earlier poster explained, warming up your engine means you'll use less fuel in total. That means less pollution, not more.

Engine oil works best when warm up to operating temperature. Also a cool down period is also recommended. If you just got off the freeway, drive around slowly for about 10 minutes to bring engine temperature down. This even more critical you have (or have added) a turbocharger. The shaft bearing on the turbo mostly uses engine oil to survive the brtual exhaust temperatures during boost. If the engine is prematurely shutdown while the turbo housing is still hot, the oil can coke in the shaft bearings. This is why performance auto stores sell turbo timers. A turbo timer lets you remove you remove your key from the ignition and the engine will continue to run for a few minutes, so the oil pump can do its work to cool the turbocharger.