Problem: 1994-96 GM 3.1L VIN M series engines have manifested excessive oil consumption as they approach the 50,000 km mark. This oil consumption has reached the 1-liter per 1,000-kilometer level. GM says that normal oil consumption is about one-third this.
Cause: One reason for such an increase in oil consumption could be the lower intake manifold gasket. After prolonged exposure to fuel-enriched air and thermal cycling, the OEM lower intake manifold gaskets take a compression set.
When this happens, a pathway is formed for oil to be drawn into the intake manifold where it mixes with the air and fuel, and is then burned in the cylinder. Due to the efficiency of the combustion process and the catalytic converter, no oil smoke is visible from the exhaust.
Solution: Replacement of the lower intake manifold gasket is required to remedy this problem. There are two intake manifold gasket designs, depending on the rocker arm design used in the engine. The ball and nut engines have an OE #12573009 gasket or equivalent; roller rocker engines are to use a gasket design equivalent to OE#12480829.