That Oil Spot in Your Driveway Isn't Going Away
You've noticed it for a few weeks now—a dark spot where you park your 2019 Highlander. And there's that faint burning oil smell after you drive. Pop the hood and you might see the culprit: oil seeping around the valve cover, making a mess of everything below.
Valve cover gasket leaks are one of the most common oil leaks on high-mileage Highlanders. The good news: it's a manageable repair.
Signs of a Valve Cover Leak
- Oil visible on engine, especially around the top edges
- Burning oil smell after driving
- Smoke from engine bay (oil dripping on exhaust)
- Low oil level between changes
- Oil drips on driveway (may follow the engine contour down)
- Spark plug wells filling with oil (V6 engines)
What's Happening
The valve cover sits on top of the cylinder head and seals the camshaft and valve train area. A rubber gasket between the cover and head keeps oil in. Over time, this gasket hardens, shrinks, and cracks from heat cycles. Eventually, it can't seal anymore.
On the V6 Highlander, there are actually two valve covers—one for each bank. Either or both can leak.
Why Valve Cover Gaskets Fail
Age and Heat Cycles
Every time your engine heats up and cools down, the gasket expands and contracts. Over thousands of cycles, the rubber deteriorates.
Hardened Rubber
Oil-resistant rubber still degrades over time. It loses flexibility and can't conform to minor surface imperfections anymore.
Over-Torqued or Under-Torqued Bolts
If someone worked on the valve cover previously and didn't torque the bolts to spec, the gasket may have been damaged or isn't sealing evenly.
The Bigger Concern: Spark Plug Wells
On V6 Highlanders, the ignition coils sit in tubes (wells) that pass through the valve cover. If the well seals fail, oil fills the spark plug wells. This can damage ignition coils and cause misfires—a more expensive problem.
Repair Options
- Replace the gasket - The proper fix. Remove the valve cover, clean surfaces, install new gasket, torque to spec.
- Replace cover and gasket together - Some covers warp over time. New cover ensures a flat sealing surface.
- Check and replace spark plug well seals - Always do this at the same time. They're cheap and labor is the same.
What It Costs
- Valve cover gasket (one side): $200 - $400
- Both valve cover gaskets (V6): $400 - $700
- Valve cover replacement: Add $100 - $200
- Spark plug well seals: $20 - $50 (parts), included in labor
- DIY parts cost: $30 - $80
DIY Feasibility
On the 4-cylinder Highlander, this is a moderate DIY job. The V6 is more challenging—the rear valve cover is harder to access, and you'll need to remove various components. Budget 2-4 hours for a V6 DIY.
Don't Ignore It
A small leak becomes a big leak. Oil on the exhaust manifold is a fire risk. Oil in spark plug wells kills coils. Letting it go leads to bigger repair bills.