Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. Symptoms of a Bad or Failing Crankcase Vent Filter

Symptoms of a Bad or Failing Crankcase Vent Filter

Bad Symptoms of Vent Filter

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


More related articles

What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P0477 OBD-II Trouble Code: Exhaust Pressure Control Valve Low
P0477 code means that the PCM has detected an abnormally low voltage reading often due to the exhaust back pressure control valve circuit.

Related questions

Q: Shield rattling on a 2012 VW Passat

No, it's not necessary. It's a shield that keeps your oil pan from getting hot. Those Volkswagens are so squirrely, if you want to talk about over-engineered German nonsense. Their oil pans are two-part oil pans on most of...

Q: I made changes to the air filter on my car

Hi there. As long as the air is still being properly filtered and the air filter is properly sealed, then you are fine. This can give you better air flow which increases the efficiency of the engine.

Q: 2007 Dodge Grand Caravan hard detonation problems

Take a compression tester and check the compression of each cylinder. This will determine how much pressure will hold in the cylinders. If the pressure is 120 or higher, then the cylinders are okay. If the pressure is lower than...