We discovered complaints surfacing about heavy oil usage between oil changes in the Grand Cherokee ZJ v8 models. We had a customer complaint about such a problem that eventually led to engine failure due to running the engine completely out of motor oil.
Our customers Grand Cherokee ZJ had relatively low miles, in the neighborhood of 120k, not a lot of miles for a Jeep and certainly not enough miles to run out of motor oil between oil changes.
Upon engine tear down, everything appeared to be normal except for large amounts of oil deposits in the intake manifold region. Anyone knows that oil shouldn’t be anywhere close to the intake manifold area, a strange clue.
After talking to the customer we discovered that he recently had a catalytic converter clog up that needed to be replaced as well, another clue.
Heres what happened, after putting the clues together we were led to believe that the two piece intake manifold was leaking on the bottom side in the oil valley area. While the vehicle was running, the gasket failure allowed the engine to draw small amounts of oil out of the valley area continually while the engine was running. This in turn over time led to the clogging up of the catalytic converter and then eventually to running the engine out of oil.
The solution to the problem is to be sure that when the engine goes in for service, remove the intake manifold and clean all surfaces. Separate the two parts, the manifold from the bottom cover plate. On the gasket surface use a thin film of rtv on both sides of the gasket and when securing the hardware to use thread locker upon assembly all the while making sure that all hardware is torqued down at the proper amount and in the right sequence. The customer shouldn’t ever have a problem again.