If your diesel has been experiencing any difficulty starting during warmer weather, make sure you take care of the problem as soon as possible. Once winter temperatures arrive your truck will only become harder to start. The following list of precautionary measures should help your diesel operate reliably throughout the winter.
Keep your fuel tanks full most of the time. Full tanks will be less likely to accumulate moisture, and full tanks help the fuel pumps move fuel through the fuel lines.
Always use the engine block heater whenever the overnight low drops below 20° F. You'll be amazed how much easier your truck will start, and your batteries and starter will last much longer as well. I normally use an electrical timer that turns on the block heater a couple of hours before I need to drive my truck.
When the temperature is near 0° F. or below, let the truck warm up for a few minutes before driving off. This will allow the engine compartment to warm, and will help prevent fuel from gelling in the engine compartment. All GM 6.2/6.5 and Duramax fuel injection systems constantly recycle fuel through the fuel return line from the injection pump and injectors when the engine is running, which warms the fuel in the fuel lines and fuel tank. This helps prevent fuel gelling in these areas. In fact, all light-truck diesel fuel systems are designed to deal with cold weather. It is the extremes in cold weather or the possibility of contaminated fuel that we diesel owners need to prepare for.
When driving in sub-zero weather, a "winter front" that covers the grille of your truck helps the engine compartment maintain a warmer temperature. Your engine will run better and this will also help prevent fuel gelling. This image is from the Fall 2002 Cabela's mail order catalog.
Untreated DF2 (diesel fuel #2) under just the right conditions can develop wax crystals at approximately 20° F. These crystals usually accumulate in the fuel filter or on the fuel strainer in the fuel tank. This accumulation can get to a point of closing off the fuel supply to the engine, and the engine will stop running. Winterized #2 diesel fuel is supposed to resist clouding down to the lowest temperature expected in a given region. As a precaution, all diesel owners can treat their own fuel during periods of extreme low temperatures, if you don't completely trust the fuel-blending at the pump. The Stanadyne Performance Formula and other national brand fuel treatments can help diesel fuel resist clouding and gelling.
If you suspect fuel gelling (or waxing) has affected your diesel, changing fuel filters can temporarily solve the problem and may allow you to drive to the nearest town. Adding an anti-gel additive to your fuel is your best bet to help solve these kinds of problems. Always carry a good anti-gel fuel treatment and an extra fuel filter with you when traveling, if there is a possibility of sub-zero weather.
For a truck that suffers from severe gelling, only towing the truck to a warm garage or shop will solve your problem. As soon as the fuel system in your truck has warmed up, treat the fuel with twice the recommended amount of anti-gel additive, then run the engine for several minutes before driving out into the cold.
If you have water in the fuel, you will have to change the fuel filter(s) and possibly purge the tank and fuel lines after they have thawed. Racor® and Stanadyne® are the only diesel fuel treatments currently mentioned by General Motors as being acceptable for their 6.5L diesel or the 6.6L Duramax® diesel engines. Whatever fuel treatment you use, ensure that it is labeled an "alcohol-free" and "water-demulsifing" fuel treatment. A water-demulsifing fuel treatment will cause any free or entrained water to coalesce, where it can be drained from your fuel filter assembly. Do not use any diesel fuel treatment containing alcohol.
Motor oil: The viscosity of the motor oil needs to be considered during the winter months because of how it affects cold engine cranking speed. Higher cranking speed helps the engine start in at least 2 ways:
1- Compression pressure is higher with a faster cranking rpm.
2- Higher cranking speeds help the fuel injection syste, generate the high fuel injection pressures necessary for the engine to start well. Minimum cranking speeds are 100 rpm cold and 180 rpm hot.
If you always have access to electricity, use a high quality 15W-40 oil like Chevron Delo 400 and keep your truck plugged in when you're not driving it. If you have to leave your truck sit in the cold for long periods, a CG-4, CH-4 or CI-4 API rated synthetic motor oil will allow easier starting than a 15W-40 petroleum oil. Mobil Delvac 1 5W-40 is an excellent synthetic diesel-rated motor oil.
