Engine Crankcase Breather Cap

What Is an Engine Crankcase Breather Cap?

Every running engine generates combustion blow-by — a mixture of exhaust gases, moisture, and oil mist that slips past the piston rings and collects inside the crankcase. Without a way to release that pressure, it can push past seals, contaminate fresh oil, and ultimately shorten engine life. The engine crankcase breather cap is a deceptively simple component with a critically important job: it allows pressurized gases to escape the crankcase while filtering out oil mist and debris before they can enter the atmosphere or the intake tract.

In a closed crankcase ventilation system, the breather cap works hand-in-hand with the PCV (positive crankcase ventilation) valve to route blow-by gases back into the intake manifold for re-combustion. In open or race-only setups, a vented breather cap releases that pressure directly to the atmosphere through an internal filter element. Either way, a properly functioning breather cap keeps crankcase pressure in check and protects everything downstream.

What to Consider When Shopping Breather Caps

• Mounting style: Breather caps come in push-on, push-in, and twist-on styles. Match the style to your valve cover opening — typically 1.25 in. or 1.22 in. O.D. holes are most common on domestic V8 engines.
• Open vs. closed system: Open breathers vent directly to the atmosphere and are popular for race or off-road builds. Closed breathers connect to the PCV system and are required for street-legal emissions compliance.
• Filter element material: Polyurethane foam and synthetic mesh elements are the most common. Both filter oil mist effectively, but synthetic elements can usually be cleaned and reused.
• Finish and aesthetics: Chrome-plated and billet aluminum options are popular for show engines, while black powder-coated and raw aluminum versions suit more functional or understated builds.
• Engine compatibility: Many breather caps are application-specific — especially for Chevy, Ford, Mopar, and AMC platforms — so always verify fitment before ordering.

Top Brands in Engine Crankcase Breather Caps

Mr. Gasket is one of the most recognized names in performance engine accessories, and their crankcase breather lineup reflects that heritage. Their chrome-plated breathers, embossed with the iconic Mr. Gasket logo, are designed to work with race car vacuum balance systems as well as OE positive crankcase ventilation applications. Some models feature an internal oil baffle with a polyurethane filter element, making them equally at home on a show engine or a weekend racer.

Moroso has built a decades-long reputation in professional motorsports for designing parts that handle extreme conditions. Their crankcase breather caps are engineered to manage high crankcase pressures found in high-output and forced-induction engines, making them a go-to choice for serious performance builders who need reliable venting under demanding conditions.

Proform Parts offers a range of engine dress-up and functional accessories that balance style with substance. Their breather caps are a favorite for enthusiasts who want clean, finished engine bays without sacrificing proper crankcase ventilation — often available in chrome and black finishes to complement a variety of builds.

Racing Power Co. rounds out the category with one of the largest selections of breather caps available, covering a wide array of domestic V8 platforms. Their broad catalog makes them a reliable source for hard-to-find fitments across Chevy, Ford, Mopar, and Pontiac applications, whether you are restoring a classic or building a dedicated track car.