What kind of oil are you using?? In the winter I exclusively use synthetic Mobil 1 in the lighter weights.. usually 10W30. If I used petroleum oils, like 15W50 the car is sluggish and barely gets out of it's own way till it comes up to temp. Mine is a 78 300CD with 285,000 miles on it and it runs wonderful on the original engine. I've ALWAYS used Mobil 1 5W20 or 10W30. Once in a while when I had it changed they forgot my instruction for the Mobil 1 and put 15W50 in it. I would know that the minute I pulled out of the driveway.