A Cummins crankcase filter removes moisture and contaminants from the air inside your engine's crankcase

The crankcase is the lower part of your engine where oil collects. As your engine runs, gases and vapors form inside the crankcase — some from normal combustion, some from moisture that condenses when the engine cools. A crankcase filter (also called a breather filter) sits on top of or inside the valve cover and traps water, dirt, and oil mist before they can damage your engine or foul the oil.

Cummins diesel engines use crankcase filters because diesel engines produce more crankcase vapors than gasoline engines do. If these vapors and moisture stay trapped inside, pressure builds up, seals fail, and oil gets contaminated faster. The filter lets pressure escape safely while keeping the inside of your engine clean.

Most Cummins owners encounter the crankcase filter during routine maintenance or when they notice oil leaking from the valve cover area — often a sign the filter is clogged and pressure is pushing oil past the seals.

Key Takeaways

  • Cummins crankcase filters trap moisture and dirt from engine vapors and should be inspected every oil change.
  • A clogged crankcase filter causes pressure to build inside the engine, leading to oil leaks around the valve cover and seals.
  • Replacement intervals vary by engine model and operating conditions, but many Cummins filters last 15,000 to 30,000 miles.
  • You can often see a clogged filter by removing the valve cover — it will look dark, wet, or packed with debris instead of white or light gray.
  • Replacing a crankcase filter is usually a 15- to 30-minute job that requires no special tools beyond a wrench and a new filter.

Where the crankcase filter sits on your Cummins engine

The location depends on your engine model and year. On many Cummins B-series engines (5.9L and 6.7L used in Dodge trucks), the crankcase filter is mounted on top of the valve cover or integrated into the valve cover itself. On some Cummins QSB and QSL engines used in commercial trucks and equipment, it may be a separate cartridge mounted on the side of the engine block.

Your owner's manual or service manual will show the exact location for your specific engine. If you are unsure, look for a cylindrical or rectangular component with a vent hose running to the air intake or atmosphere — that is your crankcase filter or breather system.

Signs your Cummins crankcase filter needs replacement

The most common warning is oil leaking from around the valve cover, especially after the engine has been running and pressure has built up inside. You may also notice a burning oil smell, or see oil mist or residue on the outside of the engine block below the valve cover.

Another sign is a hissing sound when you remove the oil filler cap — that noise means pressure is trapped inside the crankcase because the filter is not venting properly. If you open the valve cover and the filter cartridge looks dark, wet, or caked with sludge instead of dry and light-colored, replacement is overdue.

Some Cummins engines have a restriction indicator on the crankcase filter housing — a small pop-up button or gauge that signals when the filter is too clogged to flow air freely. Check your manual to see if your engine has one.

How to replace a Cummins crankcase filter

Start by letting the engine cool, then locate the filter. Most top-mounted filters are held in place by a single bolt or a twist-lock collar. Remove the bolt or unscrew the collar by hand or with a wrench, depending on the design. Lift the old filter straight up and out — it may be oily, so have a rag ready.

Inspect the sealing surface on the valve cover where the filter sits. Wipe it clean with a dry rag to remove any oil, dirt, or old gasket material. If the surface is damaged or the threads are stripped, you may need to replace the valve cover itself.

Install the new filter by reversing the steps: place it on the sealing surface, align the bolt holes or collar threads, and tighten firmly but not so hard that you crack the plastic or aluminum housing. Reinstall any hoses or clips that were attached to the old filter. Start the engine and check for leaks around the base of the filter. If you see oil seeping out, turn off the engine, let it cool, and tighten the fastener a bit more.

Replacement intervals and filter types for different Cummins engines

Cummins recommends checking the crankcase filter at every oil change and replacing it when it shows visible dirt or restriction. For many B-series engines in pickup trucks, that is typically every 15,000 to 30,000 miles, depending on how dusty your operating environment is. Heavy-duty commercial engines may have longer or shorter intervals based on the manufacturer's service schedule.

Cummins produces OEM (original equipment manufacturer) crankcase filters for each engine family — for example, the 5.9L Cummins uses a different filter than the 6.7L, and both differ from QSB or QSL filters. Using the correct part number ensures proper fit and sealing. Aftermarket filters are available from truck parts suppliers, but verify the part number against your engine model before purchase.

If you operate in a very dusty environment — unpaved roads, construction sites, or desert conditions — inspect the filter more often and replace it sooner. Moisture-heavy environments like coastal areas or high-humidity regions may also shorten filter life because more water condenses inside the crankcase.

What happens if you ignore a clogged crankcase filter

Pressure builds up inside the crankcase and pushes oil past seals and gaskets that were designed to hold back only normal pressure. This leads to oil leaks around the valve cover, oil pan gasket, and crankshaft seals. Over time, the engine loses oil faster than you can top it up, and running low on oil causes bearing wear and engine damage.

A clogged filter also allows moisture to stay trapped in the crankcase longer, which thins the oil and promotes rust inside the engine. This shortens oil life and can lead to sludge buildup on internal components. In cold climates, trapped moisture can freeze and block the vent system entirely, creating dangerous pressure spikes.

Replacing a $30 to $80 filter every 15,000 to 30,000 miles is far cheaper than repairing oil leaks, replacing valve cover gaskets, or rebuilding an engine damaged by low oil pressure.

Frequently Asked Questions

Can I drive with a clogged crankcase filter?

You can drive short distances, but not safely for long. Pressure will build and push oil past seals, causing leaks and oil loss. Replace the filter as soon as you can to prevent damage to gaskets and seals.

Is the crankcase filter the same as the air filter?

No. The air filter cleans air entering the engine for combustion. The crankcase filter cleans vapors and moisture leaving the engine's crankcase. They are separate components with different jobs.

What if I cannot find the crankcase filter on my Cummins?

Check your owner's manual or service manual for the exact location — it varies by engine model and year. You can also contact a Cummins dealer with your engine serial number, and they will tell you where it is and provide the correct part number.

Do I need to drain oil before replacing the crankcase filter?

No. The crankcase filter does not hold oil like an oil filter does. You may see some oil residue when you remove it, but you do not need to drain the crankcase. Have a rag ready to catch drips.

Can a bad crankcase filter cause white smoke from the exhaust?

Not directly. White smoke usually means coolant is entering the combustion chamber. However, a clogged crankcase filter can allow moisture to build up in the oil, which can eventually lead to coolant contamination if seals fail. Replace the filter and have the coolant level checked.