home facebook twitter instagram youtube

Excessive Crankcase Pressures, Positive Crankcase Ventilation (PCV)

Follow

Some L3T DISI engines (in completely stock form) burn oil through the engine and oil smoke pours from the tailpipe while at idle. This is due to several issues that we've found with this platform. First, the PCV source where the crankcase pressures are pulled (or sucked) comes from the engine block itself, not from the head or valve cover as is on almost all other vehicles. Pulling the crankcase ventilation from the top of the engine assembly, rather than the lower crankcase assembly as is done on the Mazda L3T DISI engine, is done to avoid pulling in atomized, liquid oil, or further contaminated crankcase gases from the crankcase housing. The crankshaft is spinning through pressurized, hot engine oil at several hundred RPM while at idle and mixes combustion chamber blow-by and engine oil into the crankcase gases. If these gases are immediately sucked into the PCV system, the probability of having significant oil contamination sent through the running engine are high.

When the PCV system pulls from this source, it can then send these contaminated gases back through the engine via the PCV exit located on the Turbo Inlet Hose (TIH). These contaminated gases are then run through the combustion chamber and if oil is present in large enough quantities, then you will visibly see the burned oil come out the tailpipe as a whitish/blue smoke. 

Another reason why the stock 1st Generation MS3/6/MPS (Gen1) PCV design is flawed is that the PCV valve and rubber hoses can get clogged with these contaminants in the crankcase gases. The valve and plumbing then won't allow the crankcase pressure to vent properly. This ends up creating excessive crankcase pressures which blocks off or impedes the oil return line from the turbo charger. Once this oil return line is impeded, the pressurized engine oil feeding the turbo has no where else to go other than through the turbo shaft seal into the relatively lower pressure intake tract when even more liquid oil is eventually sent through the engine to burn while at idle.

You can have a service update performed by your local Mazda dealer if your vehicle is still under warranty. With this TSB service update from the dealership, you will receive a new valve cover and a newer TIH which match the current design on the 2nd Generation (Gen2) MAZDASPEED3/MPS. These new pieces have implemented a better PCV design and pull the positive crankcase ventilation from the top of the engine assembly.

Alternatively, you can contact one of our many COBB Protuners to increase the idle speed targets on your calibration by approximately 100 RPM to allow the engine to pull more of the positive crankcase pressure out of the crankcase.

Have more questions? Submit a request

Comments

Powered by Zendesk