I just got my diesel e-tested last night after work....they didnt even look under the car....I would think that if you go to a "good" place they might actually look under the car!!!
i've got one buddy who will jump into his honda at work... won't even let it idle a minute at -10C and just zoom off... sure his car heats up but i wonder what kind of damage he's doing to his motor... of course 5w20 oil flows excellent in the cold weather though!
Actually, that's exactly what you are supposed to do. Just drive gently until it's up to temp. For a gasser, letting it sit there & idle just ruins your cats cos it runs rich for longer and doesn't warm up as fast.