An oil leak from the valve cover in your 2018 Toyota Highlander is a common issue as vehicles age, though appearing on a 2018 is somewhat early. The valve cover gasket seals the top of the engine where the valve train operates. When this gasket fails, oil seeps out and typically runs down the side of the engine.
Signs of Valve Cover Leak
Oil visible on the side of the engine, particularly near the top. Burning oil smell as leaked oil contacts hot exhaust manifolds. Oil accumulation on spark plug boots (in wells). Low oil level without visible puddles under the car. Smoke from the engine bay in severe cases.
Why Valve Cover Gaskets Fail
The gasket is made of rubber or silicone that hardens with age and heat cycles. This hardening causes it to lose flexibility and sealing ability. Over-torqued or unevenly torqued valve cover bolts cause uneven pressure. PCV system problems increase crankcase pressure, pushing oil past gaskets.
The 2018 Highlander Engines
The 2018 Highlander came with the 2.7L 4-cylinder or 3.5L V6. The V6 has two valve covers (one per bank), making leaks potentially appear on either side. Both engines use gaskets that can be replaced without removing major components.
Repair Considerations
Valve cover gasket replacement is a common repair. The gaskets themselves are inexpensive ($30-$100), but labor varies based on access—the V6 rear bank is more difficult. Consider replacing both valve cover gaskets on V6 engines for preventive maintenance. Also replace spark plug tube seals at the same time if equipped.