Is this something normal? I have an ST170 motor dry sumped, removed crankcase breather and added a small catch tank with a cambox cover breather and a breather hose from the dry sump tank... Car has now done about 150 miles since Iva and today was just looking over the car and noticed some oil mist that had come out of the small filter that is on top of the catch tank... No oil of note it would seem in the catch tank itself... Motor has only done about 500 miles from new....

Dave B

Not the greatest idea to remove the crankcase breather link to the intake - positive crankcase ventilation is done for performance as well as emissions gains, but it's also not unheard of for removing the "positive" bit of the ventilation to push oil seals to their limits on older engines.

Pretty normal to get oil mist even on a new engine- ever opened the oil filler cap with a running engine? I suspect a newer engine will have slightly higher breathing than a well bedded in engine also.

I was told good to remove the crankcase breather to get a vacuum in the sump.... But I am learning so open to any advice....

Dave B

Apparently the dry sump scavenge will remove the crankcase gases and create a small vacuum...

Dave B

How would you get a vacuum by removing the PCV and venting it to atmosphere? If you /blocked/ the vent and had a very high performance pump you might get some level of negative pressure from the setup if your blowby wasn't large, but if you vent the err vent out through a catchcan are you not just going to let air in? The fact that you're seeing mist suggests whatever pump is evacuating your sump is not capable of out-doing the blowby. I may not be seeing your layout properly in my head to be fair?

The PCV is blanked off... I have connected the cam box breather and a breather from the dry sump tank to the catch tank....

Dave B

OK normally the cam breather IS the PCV point. Assuming you've blanked off one breather and attached the other with the tank breather to the catch can, you're still doing the same thing as I said - your crank breather is now "just breathing" rather than pulling any vacuum in the crankcase. To pull anyvac in the crank case you'll need to block off all vent type ports and rely on the pump alone, then vent that tank. But if that pump can't keep up with the gas flow you'll blow seals. In your current setup you're just doing the same as if you just opened the crankcase vent to atmosphere.

My Zetecs (and x-flows) have run with a pipe from the crank case breather and a pipe from the rocker/cam cover to a common bottle for 25 years now with no issues. But you must remove the valve from the crank case breather box. You just get a little mist in the bottle with a good engine or a bottle full when its knackered.

[Edited on 25/11/13 by Paul Turner]