What causes a vacuum leak?

2 minutesread

Intake snorkel:

A rubber or plastic boot (snorkel) that connects the engine intake and therefore the air cleaner box can rip or crack. It is a quite common problem in older and high-mileage cars. The repair is straightforward, the snorkel must get replaced. In most cars, it’s secured by gear wheel clamps at both ends. If an intake boot isn’t installed properly at an air cleaner box (see this photo) or at a throttle body, it can cause a vacuum leak too.


Intake manifolds and gaskets:

A manifold is bolted to the engine head or plenum. With age, plastic intake manifolds warp. Gaskets and O-rings that seal the gaps harden and shrink. This causes vacuum leaks. This problem is incredibly common in many cars. Plastic intake manifolds are especially susceptible to leaks.


Plastic and rubber vacuum hoses and lines:

With age, vacuum hoses become brittle and crack or rip. The hoses and features that connect the PCV system to the manifold are especially at risk of failure. This happens because crankcase vapors contain oil, that damages the rubber or plastic, causing hoses and contours to swell and crack.


Positive Crankcase Ventilation or PCV system:

The PCV system removes blow-by gases and oil vapors from the engine crankcase. The PCV system collects the oil from vapors using an oil separator. After that, the vapors are directed into the engine intake through the PCV valve.


EGR Valve:

The EGR system directs a tiny low number of exhaust gases into the intake to lower the combustion temperature. An EGR Valve connects the manifold to the exhaust. Normally, it opens only the car is driven steady at higher speeds.


Brake booster:

A brake booster is installed between the treadle and therefore the brake cylinder. In most cars, it’s connected to the engine intake and is operated by the engine vacuum. Inside a brake booster, there’s a vacuum diaphragm. When a brake booster leaks, it creates a vacuum leak.

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