Cold Weather Operation
and the GM Diesels
Updated November 2018 -

Operating a diesel engine during the cold winter months demands that all diesel fuel and electrical systems operate normally. Diesel mechanics will tell you that their business activity picks up considerably beginning sometime in October due to cooler temperatures. If your diesel has been experiencing any difficulty starting during warmer weather, make sure you take care of the problem as soon as possible because once winter temperatures arrive your truck will only become harder to start. The following list of cold weather tips should help your diesel pickup operate reliably throughout the coming winter.

Depending on the level of humidity in your area, you should 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.

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 and combustion heat are higher with a faster cranking speed.

2- Higher cranking speeds help the fuel injection system 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, a high quality diesel-rated petroleum motor oil like Chevron Delo 400 or Rotella T 15W-40 will provide good cold weather service if you use your engine block heater overnight. If you have to leave your truck sit exposed to the cold for long periods, a CG-4, CH-4, CI-4 or CJ-4 API rated synthetic motor oil will allow easier starting than a 15W-40 petroleum oil. Royal Purple, Shell, Mobil, Amsoil and others all offer excellent synthetic diesel-rated motor oils.

The fuel tank cap used on these GM diesels are vented to allow a maximum of 2-psi positive pressure or 1" vacuum within the fuel tank. Depending on how much fuel is present in the fuel tank, a large temperature swing thoughout the day can produce a large pressure change within the fuel tank - if the cap doesn't vent properly. A bad cap vent can produce a range of engine running problems that include no starts, stalling, poor performance or air in the fuel lines. If your diesel ran normally throughout the summer, but began acting-up when the temperature began to fall, change the fuel filter as a first step in troubleshooting, but keep in mind that a plugged fuel tank cap vent can also present a problem.

If you're new to the GM diesel, the information found here should help to answer your questions as well as reduce any anxiety you might have about cold weather operation. Dealing with cold weather is really easier than you might think.

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