COOLING SYSTEM OVERPRESSURE
I own an early 2001 LB7 Duramax that has been in the shop recently because of a cooling system overpressure problem. Of course, this resulted in replacing a water pump (seal leak), thermostat(s), radiator, surge tank pressure cap, and all of the coolant hoses. All these were likely needed, but didn’t solve the problem. Now I’m dealing with a head gasket replacement project. I want to do this right. What do I need to know to prevent this from happening in the future? As you might guess, I keep the same truck for as long as I can keep it on the road. I bought this 2001 brand-new.
Wayne Stewart Calgary, Alberta
While head gaskets can and do fail in any diesel engine, the original LB7 Duramax had another problem in the form of an injector cup for each cylinder. The cups were “wet,” meaning they were made from stainless steel and penetrated the cylinder head through the water jacket. This meant, in part, that the cups needed to prevent combustion pressures from finding their way into the cooling system. So, cups can be a cause of cooling system overpressure—like head gaskets if the head-deck end of seal is broken.
When the LLY arrived in the 2004.5 model year, Isuzu obviously had thought it out a little more because the injectors were positioned differently and they had abandoned the cup design. That was good for the future of the Duramax, but several hundred thousand owners were left with the LB7 injector cup problem. It’s thought that replacing a set of injectors presents a possibility for disturbing the cup seals, resulting in combustion pressure finding its way into the cooling system—which can result in water pump seal failure, head gasket replacement (thinking that’s the problem), and all the rest.
Some years ago we speculated that a newly designed LB7 cup incorporating a threaded small end that screwed into the cylinder head should and would solve the problem of cup seal leaks. As it turns out, Industrial Injection (Industrialinjection.com) is now offering just such a product. It’s a bit pricey, but we wouldn’t do an LB7 head gasket job without these new Industrial injector cups. They should provide a permanent solution to a cup seal leak problem.
Otherwise, be sure to buy only the most recent iteration of head gaskets. GM has produced an everevolving series of head gaskets that are improved over what the engines left the DMAX facility with.