Valve cover oil leaks on your 2017 Subaru Impreza's boxer engine create oily deposits on the engine exterior and can contaminate spark plugs if the leak reaches the plug wells. The Impreza's horizontally opposed engine layout creates unique considerations for valve cover gasket service.
Boxer Engine Valve Cover Design
Unlike inline or V-configured engines with top-mounted valve covers, the Impreza's flat-four has valve covers on each side of the engine. Each cover seals not only the top of the head but also includes spark plug tube seals that prevent oil from entering the plug wells.
Leak Symptoms
External leaks appear as oil dripping down the side of the engine, potentially reaching the exhaust and causing burning smell. Spark plug well leaks pool oil around the plugs, causing misfires and degraded ignition performance. Low oil level between changes may also occur.
Why Gaskets Fail
The rubber gaskets harden and crack from heat cycling over years of operation. The boxer engine's horizontal orientation subjects gaskets to different thermal stresses than vertical valve covers. Oil additives and extended change intervals accelerate gasket degradation.
Repair Considerations
Valve cover gasket replacement on the boxer engine requires accessing the sides of the engine, which can be challenging depending on equipment present. Both sides are typically done together since they age similarly and share labor access.