DON’T LOSE YOUR HEADS

As an owner, or someone in the market for the LB7, what signs do you look for to investigate further into potential head gasket or injector problems? On the head gasket side, it’s just like any other internal combustion engine: When that head gasket seal is compromised, the motor will lose coolant, which could pressurize the degas bottle enough to blow the cap; and the upper radiator hose could also be hard—from excessive pressure—long after the engine has been shut down and cooled off. On the injector side of things, gray/white smoke on takeoff is usually the first visual sign of a problem, as excessive fuel gets dumped into the cylinders and isn’t burned efficiently. The engine oil could start being diluted by excessive amounts of fuel seeping past the piston rings to diagnose this. A basic injector balance rate test can be performed with a scanner in the OBD port. In additional, a trained mechanic can disconnect the injector return lines to check fuel return rates.

There are several reasons and a variety of opinions as to why the LB7 head gaskets fail, such as excessive overheating problems that could occur when towing or working the engine hard; and excessive boost and extreme cylinder pressures in a high-performance application that could allow the stock head bolts to stretch and actually lift the heads from the block. But one of the main contributing factors could be the head gasket design itself. In the pre-2006 Duramax engines, GM used a multilayer steel gasket that utilized a containment ring around each cylinder bore. This containment ring, for lack of a better word, used a “crimped” edge, where the outside layer would basically wrap around the other layers and crimp it all together around the cylinder bore. It has been suggested that this crimped edge would weaken after hundreds and thousands of heat cycles, eventually failing and allowing the combustion pressure to get between the gasket layers to create a leak. These leaks can happen internally, meaning coolant will find its way into the cylinders, or externally, where the coolant will seep through the head and down the sides of the engine block where you’ll see it. After recognizing the issue, GM re-designed the head gasket to what is referred to as a ‘riveted’ gasket, which is still a multi-layer steel gasket, but it no longer uses that rolled edge containment ring. This change has offered better results in the later Duramax platforms. Replacing head gaskets in the Duramax engine is a laborintensive job and requires a good stack of parts to get it back together correctly.

Luckily for Duramax owners, Merchant Automotive (MA) of Zeeland, Michigan, has

Upon close inspection of the cylinder heads and engine block, it appears the No. 7 cylinder had been the only one leaking. At this point, the heads will be dropped off at the local machine shop to be gone through, cleaned, tested for cracks, valves...

Obviously, the goal here was to get the cylinder heads off the engine so the head gaskets could be replaced. While the idea of it seems pretty straight forward, the labor time adds up quickly. Extreme care must be taken on disassembly so that foreign...

There it is, the tell-tale signs of a blown head gasket. On this truck, considered low mileage at just 86,000, it’s obvious the passenger No. 7 rear gasket had let go allowing coolant to enter the combustion chamber. An updated GM head gasket supplied...