Oil drips on your garage floor and an oily smell from the engine bay of your 2019 Mitsubishi Montero point to one of the most common engine leaks: the valve cover gasket. While this leak isn't immediately catastrophic, ignoring it can lead to more serious problems and environmental contamination. Here's how to diagnose and address valve cover oil leaks.
Symptoms of Valve Cover Leak
- Oil visible on valve cover or cylinder head
- Oil dripping onto exhaust manifold (smoke, burning smell)
- Oil pooling around spark plug wells
- Oil spots under the vehicle
- Low oil level between changes
- Burning oil smell from engine bay
- Oil on engine accessories below valve cover
Understanding Valve Cover Leaks
The valve cover sits atop the cylinder head, protecting the valvetrain and containing oil that lubricates the camshafts and valves. The gasket between the valve cover and head seals this oil inside. Over time, heat cycling causes the gasket to harden, shrink, and crack, allowing oil to escape.
Common Causes
Aged Gasket
Rubber and composite gaskets deteriorate over time, especially with repeated heating and cooling cycles.
Solution: Replace the valve cover gasket.
Over-tightened Bolts
Valve cover bolts don't require much torque. Over-tightening crushes the gasket, causing it to fail prematurely.
Solution: Replace gasket and torque bolts to specification.
Warped Valve Cover
Aluminum valve covers can warp from over-tightening or heat, preventing proper sealing.
Solutions:
- Check cover flatness with a straightedge
- Machine or replace if warped
Cracked Valve Cover
Impact damage or thermal stress can crack the cover itself.
Solution: Replace the valve cover.
PCV System Issues
A clogged PCV system builds crankcase pressure, forcing oil past seals and gaskets.
Solution: Check and service PCV system.
Why It Matters
While valve cover leaks seem minor, they can cause:
- Fire hazard: Oil on hot exhaust components
- Spark plug fouling: Oil in plug wells causes misfires
- Accessory damage: Oil on belts and alternator
- Low oil level: Potential engine damage
- Failed inspections: Many states fail vehicles with visible leaks
Diagnosis Steps
- Clean the area: Use degreaser to clean oil from engine
- Add UV dye: Dye helps trace the leak source
- Run engine: Allow to warm up and observe
- Identify source: Determine if leak is gasket or cover
- Check bolt torque: Verify bolts aren't loose
- Inspect PCV: Ensure system isn't building pressure
Repair Process
- Remove components blocking access (air intake, wiring, etc.)
- Remove valve cover bolts in proper sequence
- Remove valve cover carefully
- Clean all gasket surfaces thoroughly
- Clean spark plug wells of any oil
- Install new gasket (some require RTV at corners)
- Reinstall cover and torque bolts to specification in proper sequence
- Reinstall all removed components
- Run engine and check for leaks
Repair Costs
- Valve cover gasket set: $30-$100
- Labor: $150-$400 (V6 may have two covers)
- Valve cover replacement: Add $100-$300
- Total typical repair: $180-$500
This is a relatively affordable repair that prevents more expensive problems. DIY is possible for experienced home mechanics, but the V6 layout may make access challenging.