LLY - Water Pump Issues

Texas Diesel Company has the factory GM computer in-house! This allows us to quickly and effectively diagnose your vehicle saving you both time and money. We are also able to provide in-house programming of all components & modules installed in your vehicle, no different than the Chevrolet/GMC dealership would. If you’re another local shop interested in having us re-program a module for you, please call (903) 292-0400

If you find that your water pump is needing replacement often, it may be a good idea to take a look at your cooling system to identify what the root of the problem is. In most cases, we find that bad head gaskets or EGR cooler & a faulty coolant reservoir cap are to blame. We blame the cap only because it isn’t doing its job correctly. Your coolant reservoir cap is set to release pressure at 15PSI. This is a fail-safe to ensure your cooling system doesn’t over-pressurize. The cooling system for LB7, LLY, LBZ & LMM is only rated for 15PSI. Should the cooling system ever reach this pressure, the cap should begin releasing pressure to bring the system back down to its operating range. This is NOT normal operating practices. In this case we need to look at 2 different components of your engine. The EGR cooler or your cylinder head gaskets. Either or both of these components could be to blame in increased coolant pressure. In some cases, we find that a failed EGR cooler can also cause a blown head gasket due to the loss of coolant and increased cooling temps in the engine.


One way to identify a bad head gasket is by energizing the cooling system to the maximum PSI of the system (this PSI will be printed or stamped on the cap) with a radiator pressure tester kit. If you just need to use this tool once or twice, we recommend purchasing the Pittsburg Automotive one from Harbor Freight. Wait to see if the pressure drops over a period of an hour. If the pressure drops, we recommend removing all glow plugs and then re-pressurizing the system. Make sure to keep the pressure around the maximum PSI of the system and then using a borescope, look for signs of coolant leaking into each cylinder through the glow plug hole. If you don’t have a borescope, you can attempt to turn the engine over and identify which cylinder has an excessive amount of fluid escaping from the glow plug hole. Make sure to wear safety glasses while doing this, it will make a mess.

One way to test your EGR cooler for leaks is by submerging the cooler in a tub of water. Securely block off 1 of the coolant connections (You can attach a rubber hose with a screw clamp to the cooler and use a bolt with RTV clamped on the other end of the hose if necessary). On the other connection of the EGR coolant passage, attach a rubber hose with a hose clamp and a pressure regulator. Attempt to energize to 3-5PSI and submerse the cooler into the bucket of water. Check to see if any air is escaping from the air passages of the EGR cooler, if bubbles are present, then you have a faulty EGR cooler.