Originally Posted by F18

Ryan,.....are you storing the car away for the winter or keeping it on the road? For winter running in an old 300SD I would definetly change the fuel filter...the older mechanical injection pumps start to loose pressure the older they get and they don't need any additional resistance like a dirty fuel filter to inhibit its ability to deliver cold gelling fuel to the injectors. Make sure your block heater plug is handy and use it when temps drop to 20deg. F or less.. . cold starts will be quicker with less strain on the battery. If your using 15w40 oil for summer drop it down to 10w40 or 10w30 depending how cold your winters are. If your winter temps get down to stretches of 10deg or less plan on cutting (diluting) your diesel with some kerosene. Keep a 5 gal can of it around and add 10% and up to 20% to your tank to assist in cold starts as needed (economy will drop some but it beats having to get towed somewhere). Also trickle charge your battery if all your doing is short commutes.
All other winter preparations are the same as any other car.