The coolant system tank for vehicles with the L5P diesel engine is a new design with two tank caps. One cap is low on the side of the tank and is a standard vented cap with right-hand threads. The fill cap on the tank top is non-vented and features a left-hand thread to prevent the installation of a non-vented cap where a vented cap is required. This new tank design is necessary due to space constraints in the engine compartment and the required placement of the tank lower than usual in the compartment, relative to the engine. GM-52098-A is a left-hand adapter that threads on the tank to allow pressure testing of the coolant system with the previously essential GM-24460-A Pressure Tester.  It also includes a center core with O-rings that seal off the tank vent port, allowing the test to be run correctly. Due to the fill cap being a non-vented cap, an adapter to pressure test the fill cap is not needed.