Say you're going house hunting... you have to make about 15-20 stops within 4 hours. Is it better for the engine to leave it running the whole time or to shut it down when you're not in it? Assume a non-turbo engine.

Yes, I know it's illegal to leave an idling car unattended.

 

Depends. What kind of car? Any mods?

I would just turn it off. If its hot enough, the radiator fans will kick in automatically.

 

in some cars the fans wont come on when the car is off!

do like a **** did round here on a N/A car and buy a turbo timer, he thinks its really cool to have his car idle for a minute after he's switched it off and walked away!