In good condition a later model MB diesel can idle all day in cold weather and never heat up. With the weather we've been having here, if I get stuck by a train (not too unlikely, alas), the temp gauge won't go over 50 until I drive it. This is normal -- the engine is very efficient and the heat, after all, is wasted energy. You will have to drive it to get it warmed up.

My 87 300D is very sluggish at first when it is very cold, so I let it idle a minute or so before driving off, and even then it is very slow to respond to the pedal. I suspect this is mostly due to the turbo not spinning very fast, as it returns to normal as soon as the turbo spools up. I just drive slowly for the first mile or so.

I don't get heat or blower for about a mile and a half, by which time the temp gauge is around 50. Takes 5 min or so of driving to get full heat.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!