The intake manifold gasket seals the manifold to the cylinder head. On many engines it seals only air and fuel; on others — particularly many V-type engines — it also seals coolant passages that run through the manifold. That difference determines the symptoms when the gasket fails.
Symptoms of a Vacuum Leak
- Rough or high idle.
- Lean fuel trim codes such as P0171 or P0174.
- Hesitation or poor acceleration.
- A hissing sound at idle near the manifold.
Symptoms of a Coolant Leak
- Coolant loss with dampness or crusted residue at the manifold ends or corners.
- Coolant in the oil (milky oil) if the leak is internal into the valley.
- Overheating in severe cases.
A failed intake gasket that leaks coolant internally can look like a head gasket failure, so diagnose carefully before condemning the head gasket.
How to Diagnose
- Smoke test: a smoke machine introduced into the intake will show escaping smoke at the leak.
- Fuel trim data: high long-term fuel trims at idle that improve at higher RPM suggest a vacuum leak.
- Cooling system pressure test: look for seepage at the manifold ends and check the oil for coolant.
Replacement Tips
- Clean the head and manifold sealing surfaces carefully, and keep debris out of the intake ports and lifter valley.
- Check the manifold for warpage, especially on aluminum manifolds and after overheating.
- On V-engines with end rails, follow the instructions for sealant at the corners where the end seals meet the side gaskets.
- Use the gasket designed for the application. Many modern engines use molded rubber seals in a carrier or individual port seals that must sit fully in their grooves.
- Tighten the bolts in the specified sequence and stages, then recheck where required.
- Refill and bleed the cooling system completely and recheck for leaks after the engine reaches operating temperature.
Evergreen Intake Manifold Gaskets
Evergreen intake manifold gaskets and sets are engineered with Eversealed Technologies and identified by application. Use the Evergreen eCatalog to find the right set. Browse Evergreen intake manifold gasket sets.
