If you have a radiator type oil cooler, it is a good idea to cover it partially in very cold weather, it prevents overcooling the oil. However, if you forget to uncover it later, you will fry the engine, so I recommend leaving it alone.

If you have a good thermostat, covering the radiator isn't going to do anything. The reason big trucks and buses had the cover is that they had partial flow thermostats -- there was a hole in the closing plate -- and the result was serious over-cooling in very cold temps. Bad design, use to prevent serious overheating with a bad thermostat or something.

Moderate load is the best way to warm up the engine. An MB diesel will NEVER reach operating temp at idle in the drive in cold weather -- must be driven.

If you cannot avoid the highway before you get up to temp, at least drive gently until at least 40 C, no full throttle starts, and try to stay out of the turbo as much as possible. Otherwise, keep the oil changed and don't do any more short distance, cold operating temp driving than you must.

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!