Intake Manifold Gasket Leak
Symptoms
Coolant leak at the junction of the intake manifold and cylinder heads. May present as coolant loss without a visible external leak (coolant enters the intake ports), or as a coolant stain on the side of the engine. Engine may run rough or misfire if coolant enters the combustion chamber.
Cause
The intake manifold gasket on the 3.8L V6 is a composite material that deteriorates with heat cycling. Dex-Cool coolant (used by GM) has been implicated in accelerating gasket deterioration, though this is debated. The gasket sits between an aluminium intake manifold and iron cylinder heads, different thermal expansion rates stress the gasket.
Fix
Replace the intake manifold gasket set.
The job requires removing the intake manifold, fuel rail, and associated wiring.
Parts: $80-150 for a quality gasket set (Felpro is the standard recommendation).
Labour: 4-6 hours.
This is one of the most common jobs on the 3.8L V6, and any competent home mechanic can tackle it with basic tools and a workshop manual.
Retorque the intake manifold bolts to 20 Nm in the specified sequence, over-torquing warps the manifold and guarantees a future leak.
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