Subaru Crankcase Breather Valve

What does a crankcase breather do?

A crankcase breather, also called a crankcase breather valve or crankcase vent valve, is a component in an engine that helps regulate the pressure and ventilation of the crankcase, which is the area where the engine's pistons move up and down.

A crankcase breather valve works by allowing fresh air to enter the engine's crankcase while facilitating the release of gases and vapors. It typically consists of an inlet, a ventilation passage, and an outlet. As the engine runs, blow-by gases and oil vapor accumulate in the crankcase. The crankcase breather draws in fresh air from the environment through its inlet, displacing the accumulated gases and vapors. Any oil or liquid contaminants are separated and collected within the breather. The cleaned gases and vapors then exit the breather through the outlet and are redirected back into the engine's intake system. This process helps regulate crankcase pressure, prevent the buildup of harmful substances, and reduce emissions. By maintaining proper ventilation, the crankcase breather ensures the efficient operation of the engine and contributes to a clean and well-functioning crankcase.

Crankcase breather blocked symptoms

When a crankcase breather becomes blocked or restricted, it can lead to several symptoms and potential issues in the engine:

1. Increased oil consumption: Blockage can lead to higher oil consumption and potential leaks.
2. Poor engine performance: Reduced power, rough idling, or hesitation during acceleration.
3. Excessive crankcase pressure: Pressure buildup causes oil leaks from various engine components.
4. Blue/white smoke from exhaust: Oil enters the combustion chamber, resulting in smoke.
5. Engine misfires/rough running: Improper air-fuel mixture leading to misfires and decreased fuel efficiency.

FAQs about Crankcase Breather Valve

Question: How often should I inspect or replace the crankcase breather valve?

It is recommended to inspect the crankcase breather valve during routine maintenance intervals, typically every 30,000 to 60,000 miles (or as specified by the vehicle manufacturer).

Question: How can I test if my crankcase breather valve is functioning properly?

One way to test the crankcase breather valve is to remove it from the engine and shake it. If you hear a rattling sound, it indicates that the valve is working correctly. Besides, you can also inspect the valve for any signs of blockage or damage.

Question: Can a blocked crankcase breather valve affect fuel efficiency?

Yes, a blocked breather valve can disrupt the proper air-fuel mixture in the engine, potentially leading to decreased fuel efficiency. If you notice a sudden decrease in fuel economy, along with other symptoms like rough running, it is advisable to have the breather valve checked.

Question: Is it necessary to replace the entire breather assembly, or can individual components be replaced?

The breather assembly typically consists of multiple components, including the valve itself and associated hoses. In some cases, only specific components may need replacement, such as a clogged hose or a faulty valve. However, depending on the design and availability of parts, it may be more practical to replace the entire breather assembly for optimal performance.