Symptoms of a Bad or Failing Crankcase Vent Filter

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Virtually all vehicles on the road today are equipped with internal combustion engines that have some sort of crankcase ventilation system. Internal combustion engines inherently have at least a small amount of blow by, which occurs when some of the gases formed during combustion escape past the piston rings and down into the engine’s crankcase. The crankcase ventilation system works to relieve any pressure from the engine’s crankcase attributed to blow by gases by rerouting the gases back into the engine’s intake manifold to be consumed by the engine. This is necessary, as excessive crankcase pressures can cause oil leaks to form if allowed to build too high.

The gases are usually routed through a PCV valve and sometimes a crankcase ventilation filter or breather filter. The crankcase ventilation filter is one of the only components of the crankcase ventilation system, and is therefore an important piece in maintaining the functionality of the system. The crankcase vent filter works the same way as any other filter. When the crankcase ventilation filter needs servicing, it will usually display a few symptoms that can alert the driver that attention is required.

1. Oil leaks

Oil leaks are one of the symptoms most commonly associated with a bad crankcase vent filter. The crankcase filter simply filters the blow by gases to make sure that they are clean before they are rerouted back into the vehicle’s intake manifold. Over time, the filter can get dirty and restrict the air flow, and therefore pressure relieving capacity of the system. If the pressure builds too high, it can cause gaskets and seals to blow causing oil leaks.

2. High idle

Another symptom of a potential problem with the crankcase vent filter is an excessively high idle. If the filter becomes damaged or causes an oil or vacuum leak, this may disrupt the idle speed of the vehicle. Usually a high idle is a potential indication of one or more problems.

3. Decrease in engine performance

A decrease in engine performance is another symptom of a potential problem with the crankcase vent filter. If the filter becomes clogged and causes any vacuum leaks, this may cause a decrease in engine performance due to the disturbance in the air-fuel ratio. The vehicle may experience a decrease in power and acceleration, especially at low engine speeds. These symptoms can also be caused by a variety of other problems as well, so having the vehicle properly diagnosed is highly recommended.

The crankcase filter is one of the few components of the crankcase ventilation system, and is therefore important in maintaining full functionality of the system. For this reason, if you suspect that your crankcase vent filter may be having an issue, have the vehicle serviced by a professional technician, such as one from YourMechanic. They will be able to replace your failing crankcase vent filter and perform any services that may be required for the vehicle.


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