When your engine is running, the combustion pressure pushes unburned fuel and gases from the combustion chamber to the crankcase. They pass through the piston rings, where they could leak, resulting in blow-by gases and harmful emissions.
The positive crankcase ventilation (PCV) system prevents issues by recirculating the vapors to the engine’s induction system, which has cylinders that burn them. The crankcase filter is one of the system’s crucial parts.
The PCV is connected to manifold vacuum and may have a valve with a spring and plunger or it may simply be a fixed orifice in the rocker arm cover such as you see on 4.0L Jeep Cherokee engines that have a replaceable rubber PCV orifice at the rear of the rocker arm cover. Some Chevy V8 pickups have a PCV orifice built into the rear of the left hand rocker arm cover.
The reason is that the intake stream provides the clean air needed, and since that air is being drawn through the MAF sensor, it is also factored into the fuel trim. If you remove the oil filler cap, PCV air will begin to enter there as an unmetered air feed, and the PCM will skew the fuel trim due to inaccurate mass airflow readings.
Older vehicles with round air cleaners typically had a crankcase filter that was part of the oil filler cap or they’d have a closure hose leading from the top of the oil filler cap to connect to the nipple on a plastic housing with a foam or fiber filter that was just inside the air cleaner housing. You can see it when you remove the top of the air cleaner.
Older vehicles with round air cleaners typically had a crankcase filter that was part of the oil filler cap or they’d have a closure hose leading from the top of the oil filler cap to connect to the nipple on a plastic housing with a foam or fiber filter that was just inside the air cleaner housing. You can see it when you remove the top of the air cleaner.
–Richard McCuistian, ASE Certified Master Automobile Technician
If the PCV side of the system becomes clogged or loses its vacuum, the crankcase vapors naturally reverse course and are funneled into the air cleaner.
The crankcase filter cleans the blow-by gases or escaped gases to remove contaminants like dust and dirt that will inevitably be drawn to the filter by the crankcase ventilation.
The crankcase filter is usually on the breather hose on top of the crankcase. It could also be on the valve cover, depending on the vehicle. See opening text.
Dirt, debris, and other deposits can clog the crankcase filter over time. Here are the telltale signs that your vehicle’s filter is clogged:
Oil in the air cleaner is a telltale sign that the PCV side of the system is clogged and the blowby is coming back through the filter and into the air cleaner.
A blocked or clogged filter builds pressure, which leads to blown seals or gaskets that cause oil leaks. Of course, for that to be the case, both the PCV valve and the crankcase filter must be totally clogged. If one is clogged but not the other, it won’t blow seals.
If the powertrain control module (PCM) detects any problem in the crankcase filter, it will illuminate the check engine light. Mechanics use a scanner tool to get the on-board diagnostics (OBD) code that indicates the issue from the system.
For example, if the tool logged a P1507 code, which means “Crankcase Filter Restriction,” it indicates that there’s something wrong with the filter.
Remember that other faulty parts can exhibit the same symptoms as a clogged crankcase filter. So be sure to cross-check the other signs or let a mechanic check your vehicle for a proper diagnosis.
If your crankcase filter is clogged, it might be due to the following:
Engine oil can become thick and sludgy when it’s old or contaminated, which clogs the crankcase filter.
The crankcase filter traps debris to prevent it from contaminating the oil. The dirt builds up over time, eventually clogging the filter.
Carbon deposits are a result of incomplete fuel combustion. They create a wall of black soot that hardens and blocks the passageway.
Moisture can build up in the crankcase filter, especially if the engine often runs at low temperatures. It tends to mix with other contaminants, which clogs the filter.
Keeping the crankcase filter clean helps maintain high engine performance. For example, if it’s clogged, it could cause oil contamination, resulting in sludging, engine wear, and power loss.
This might be caused by a disconnected PCV valve vacuum hose, but the crankcase filter can’t cause rough idle.
Yes, you can clean the crankcase filter on your own, provided that you’re familiar with your vehicle’s PCV system and have the tools and know-how needed for the task.
Experts recommend changing the crankcase filter when it’s damaged or at least once every two years.
It’s best to replace the filter every 25,000 miles or every two years, depending on which comes first. The lifespan of a crankcase filter depends on the filter type and the conditions of the engine.
Some factors might accelerate the need for replacement, such as weather conditions and the frequency of oil changes. It’s also worth noting that some manufacturers have recommended filter replacement intervals.
If you spot the symptoms of a clogged crankcase filter, address them immediately to prolong and preserve your vehicle’s performance and prevent irreversible damage. Take your ride to an auto repair shop as soon as possible.
If it’s time to replace your crankcase filter, it’s best to do so as soon as possible. A clogged crankcase filter can lead to broken seals and gaskets in your PCV system as the pressure builds up behind it. Thankfully, CarParts.com is here if you need a new filter.
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Place your order for a new crankcase filter element and other crankcase parts here at CarParts.com.
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