Guys,

When I lived in Germany, taxicabs idled for hours on end, every day, all winter. Gasoline engined taxis would shut down and start up whenever they had to move or drive a fare somewhere. I do not think any Diesel can maintain a normal operating temperature at idle in the winter, as they run very efficiently at idle and too little waste heat to reach normal operating temperature. I know from personal experience over the last 30 years that Mercedes Diesel automobiles cannot maintain cabin temperatures in very cold weather at idle, and I experienced this again this year in New Hampshire at -5*F in the 1998 E300 TurboDiesel. A high idle speed adds next to no load so that had little or no net effect (I tried that too with my right foot).

If you experience an increase in smoking at idle just by idling for longer periods I would suggest you look at valve guides and seals. Most of these older engines are slightly starved for air at idle and the intake manifold is under vacuum. This will make a worn set of guides and seals misbehave. Once you get a layer of crud burned and coked on to the manifold side of the valve poppet, it can reduce your compression and make more smoke.

A well running Diesel engine is not going to suffer from long periods of idling, although it might be wise to block off the radiator enough to try to raise the temperature you reach. In a 220D or a 240D without a fan clutch, this is nearly a requirement or the engine will run clattering loudly most of the time due to the low operating temperature (I am speaking of really cold weather, well below freezing).

Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)