Oil Filler Caps

Has the plastic cap on your valve cover worn out, or should the engine bay match the rest of your build? Billet oil filler caps seal the filler opening tightly and are available in several colours and variants, e.g. with a breather or a baffle. This category is for you if you want to replace or upgrade a stock part.

What an oil filler cap does

The cap closes the filler opening so the oil stays in the engine while dirt and moisture are kept out. A billet cap typically replaces the original part and can match other parts in the engine bay, e.g. new valve covers or an engine dress-up kit. Some models have extra features: a breather cap can vent crankcase gases, while a baffle, as in the Radium Engineering GM LS Baffled Oil Cap, can limit oil splashing at the cap.

How to choose a cap

Start with fitment, then choose function and finish:

• Thread and engine: Caps are made for specific engines and threads, e.g. the Skunk2 Honda Billet Oil Cap with M33 x 2.8. Always check the part number against your engine.
• Type: Sealed cap, breather model such as the Torque Solution Billet Breather Oil Cap, or a baffled model. Whether a breather makes sense depends on the rest of the engine's crankcase ventilation.
• Sealing: Check that a gasket or O-ring that fits the opening is included.
• Colour and finish: E.g. red, blue, gold or black, like the Cobb Subaru Oil Cap - Stealth Black.

Mishimoto offers oil filler caps for Honda and Subaru, for example, and HKS has caps for the 86/BRZ as well as Nissan/Honda. The category also includes brands such as GReddy and Turbosmart. See the full valve covers and dress-up parts group.

Frequently asked questions

What is the difference between a sealed oil cap and a breather cap?

A sealed cap simply closes off the opening. A breather cap lets crankcase gases escape, which can cause a little oil mist in the engine bay. Whether that is relevant depends on the engine and the rest of the crankcase ventilation.

Why is oil seeping around my new cap?

Typically it is caused by a missing, damaged or incorrectly seated gasket, or the cap not being screwed all the way down. Also check that the thread matches the engine. Tighten by hand and avoid tools that can damage the thread and gasket.

Does a billet oil cap need maintenance?

Wipe the cap clean at oil changes and check the gasket for cracks or hardening. If a breather model has a filter, it may need cleaning depending on the product. Avoid harsh cleaning agents that can affect the colour and finish.