Mazda 3 Pcv Valve And Catch Can: What to Do

The PCV (positive crankcase ventilation) valve on your Mazda 3 is responsible for routing blow-by gases from the engine crankcase back into the intake to be burned off. When it fails or gets clogged, you'll typically see oil consumption, rough idle, or a build-up of oily sludge in your intake manifold. Fitting a catch can intercepts those oily vapours before they contaminate your intake, which is a worthwhile upgrade especially on higher-kilometre engines.

What Causes It

• PCV valve failure -- the valve is a simple spring-loaded check valve that wears out over time, common on the 2.0L and 2.5L SKYACTIV-G engines in 2013+ Mazda 3 BM/BN models
• Clogged orifice -- carbon and sludge build-up blocks the valve, particularly if the car has had infrequent oil changes
• High oil consumption -- worn piston rings increase crankcase pressure, pushing more blow-by through the PCV system than it can handle
• Intake valve carbon build-up -- direct injection engines like the SKYACTIV-G don't wash the intake valves with fuel, so oily vapours from the PCV deposit carbon directly onto the valves
• Cold climate or short trips -- condensation mixes with blow-by and forms a milky sludge that restricts flow through the valve

What to Do Right Now

1. Locate the PCV valve -- on the SKYACTIV-G, it's integrated into the valve cover on the top of the engine. There is no separate serviceable valve you can pull out; the assembly is part of the cover itself. The valve cover has several factory bolts along its perimeter that are suitable for catch can bracket mounting.
2. Check for symptoms -- with the engine warm and idling, remove the oil filler cap briefly. Excessive vapour or pressure puffing out indicates the PCV system is struggling.
3. Inspect your intake -- if you're past 60,000 km on a direct injection model, pull the intake pipe and check the throttle body for oily residue. Heavy build-up means your PCV has been venting unfiltered for a while.
4. Install a catch can -- mount it in the engine bay using one of the valve cover bolts as an anchor point. Route the breather hose from the PCV outlet through the catch can before it returns to the intake.
5. For a cost-effective kit, look at the Mishimoto MMBCC-MAZ3-14 catch can, designed to fit the 2014+ Mazda 3 and priced around $180-220 AUD. It comes with all fittings and mounts cleanly without modifying factory components.

When It's Serious

If you're seeing white smoke from the exhaust at operating temperature, oil pooling in your intake manifold, or a rough idle that won't clear up, stop driving and get the engine inspected. These are signs that crankcase pressure has been uncontrolled for long enough to cause intake valve carbon deposits serious enough to affect combustion, or that oil is being pushed past seals.

An engine that smells of burning oil inside the cabin, or that is losing more than 500ml of oil between services with no visible external leaks, needs a workshop assessment before more kilometres are added. Continued driving risks contaminating your catalytic converter and compounding what is otherwise a straightforward fix.