Find out why you've got so much blow by. Catch can is a band aid on a bullet hole.

 

Any suggestions of what to look for? We've done a compression and leak down and it all seems fine. I'm a bit stuck as to what to investigate next.

 

How did you perform the leakdown and what kind of numbers did you get? Oil spray from a breather is a sure sign that the crankcase is being pressurized. That happens when you have blowby. A pressurized crankcase causes many problems.

You want the crankcase to always be under vacuum. That is why the factory used two PCV lines. One connects to the intake manifold to provide vacuum to the crankcase when the engine is pulling a vacuum (idle, no load type conditions) and the other runs from the intake side of the turbo to provide vacuum when the engine is under boost. These two line make certain that the crankcase is always under vacuum.

If you were to remove either of those lines and replace it with a catch can, the system will not work properly. The worst case is if you are to remove the one that runs from the intake side of the turbo. This allows the crankcase to become pressurized at the worst possible times, under load and boost.

I would bet money that if your leakdown tests show fine your oil consumption would decrease if you put a properly functioning PCV system back on the car.

 

I think this is exactly what is going on, and I appreciate you confirming my suspicion. I think there was some minor leaking from a failed PCV, and so the shop that built my motor went and ventilated both fittings to an open catch can and all that managed to do was dump copious amounts of oil all over the engine bay.

My plan at this point is to swap out to a Saikou Michi catch can set-up, put in a brand new PCV, and run the car hard to see if I continue to accumulate more oil.

The shop who built the motor also did the compression and leakdown, so I'll also confirm their numbers by doing my own test.

Thanks for the tips. It's nice to have some experienced mechanics active on the forums.

 

Check the valves themselves to be sure they are working. If one or both are stuck the system is useless.

 

I get checking the PCV that screws into the back of the valve cover, but which is the other "valve"?

 

you should be able to pull that whole elbow off and the PCV is connected to it. Shake it and you should be able to hear/feel it almost clicking. if not that means it is stuck and junk. The PCV valve is minor considering what it does, open when cruising or idle, its the Breather you want to make sure is routed back into the intake to create vaccum under boost. On a side not, from my understanding, a stroker motor will have a little bit more blow by than a stock 2.0 so it might look bad but usually isn't.

 

Curious as to how displacement affects blow by. That's a new one.

 

probably referring to a built motor opposed to an OEM one, though i see how it can be read that way

 

Piston speed and differences in compression?

 

Thanks for the tips.

 

Peter,

I recently purchased the the saikou michi cans and am quite pleased with them. They retain OEM function but remove the nasty stuff.

As for the PCV valves, there is actually only one valve on the back of the valve cover. This is the line that feeds into the IM. Remove it and make sure it acts as a check valve (allows flow in one direction and doesn't in the other).

Good luck.

John

 

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