Left-Hand Thread Cooling System Pressure Test Adapter

The cooling system surge tank for 2017 Silverado and Sierra models equipped with the 6.6L Duramax diesel engine (RPO L5P) features a new design with two tank caps. The fill cap on top of the tank uses a left-hand thread and requires a Cooling System Pressure Test Adapter to pressure test the system.


The tank is placed at a low position in the engine compartment, in relation to the engine, due to space constraints. Based on its location, the tank was designed to have the coolant at the top and the air portion at the bottom of the tank to ensure that the coolant will be at the highest level in the cooling system.


Vented and Non-Vented Tank Caps


The cap located on the lower outboard side of the tank is a standard vented cap with right-hand threads that vents excessive cooling system pressure. (Fig. 11, #2) The cap on the tank top is a non-vented fill cap and has left-hand threads (Fig. 11, #1); this eliminates any attempt at installation of non-vented cap where a vented cap is required. Turn the fill cap clockwise to remove the cap or counter clockwise to install it.


Fig. 11


The top tank cap has two seals (the side surge tank cap also has two seals) to protect from hot fluid exiting through the top portion of the neck itself during hot engine conditions.


Cooling System Leak Testing


The Cooling System Pressure Test Adapter (GE-52098 or GE-52098-A) is a left-hand adapter (Fig. 12) that threads on the tank to allow pressure testing of the cooling system using the previously released Cooling System Pressure Tester (Essential tool J-24460-A, or EN-24460-A).


Fig. 12


The Cooling System Pressure Test Adapter also includes a center core with O-rings that seals off the tank vent port so the test can be run correctly. (Fig. 13) Due to the fill cap being a non-vented cap, an adapter to pressure test the fill cap is not needed.


Fig. 13


TIP: During testing, do not exceed the pressure rating that is printed on the vented cooling system surge tank cap on the lower side of the tank. The cooling system should hold the rated pressure for at least two minutes. Observe the gauge for any pressure loss and inspect the cooling system for any system leaks.


The Cooling System Pressure Test Adapter (GE-52098 or GE-52098-A) is available through www.gmtoolsandequipment.com.


– Thanks to Chuck Berecz and Chris Semanisin


Updated 11/20/17

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  1. That’s correct. The top tank cap does have two seals, not three. There was a late design change to the cap. The article has been updated.

  2. Chris Jennings says:

    Hello, the following statement is incorrect :

    “The top tank cap also has three seals (instead of the two seals used in the side surge tank cap) to protect from hot fluid exiting through the top portion of the neck itself during hot engine conditions”

    I’ve checked two 2017 trucks and both only have two seals at the top radiator cap.
    I was chasing a coolant loss and thought the cap was the culprit.

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