Proper Coolant Level on the 6.6L Duramax Diesel Engine

A Low Coolant message may be displayed on the Driver Information Center of some 2017-2018 Silverado and Sierra models equipped with the 6.6L Duramax diesel engine (RPO L5P). An inspection of the radiator surge tank may appear to show a low coolant condition.

The low coolant level in the radiator surge tank may be due to the fill process at the assembly plant, which cannot purge all of the air from the cooling system and the surge tank. After the engine has been thermally cycled, air rises and causes the coolant to become lower than when initially filled.


Coolant Levels

During a Pre-Delivery Inspection (PDI), the coolant level may appear low, but is at a level high enough to keep the Low Coolant message off.

During PDI, coolant should be added to fill the upper chamber of the radiator surge tank. (Fig. 6)

Fig. 6

A coolant level that is low enough to turn on the Low Coolant message will be below the horizontal line across the radiator surge tank. (Fig. 7) The horizontal line is a baffle inside the surge tank that keeps the coolant from sloshing inside the tank and tripping the coolant level sensor, which is located below the baffle.

Fig. 7

A full coolant level will show the coolant at the bottom of the radiator surge tank fill neck. (Fig. 8)

Fig. 8


Filling the Tank

If a low coolant level is found, add one quart (0.946 liter) of Dex-Cool® coolant to the upper chamber of the coolant surge tank in order to bring the level up to the bottom of the surge tank fill neck.

TIP: The L5P diesel engine radiator surge tank has two different surge tank caps. The fill cap used to fill the system is located on top of the tank. It is a non-pressurized radiator surge tank cap with left hand threads.

Refer to Bulletin #17-NA-110 for additional information.

– Thanks to David MacGillis

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