Dave Bailey
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| posted on 24/11/13 at 07:52 PM |
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Engine breathing
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
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coyoteboy
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| posted on 24/11/13 at 08:35 PM |
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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.
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Dave Bailey
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| posted on 24/11/13 at 08:39 PM |
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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
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Dave Bailey
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| posted on 24/11/13 at 08:45 PM |
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Apparently the dry sump scavenge will remove the crankcase gases and create a small vacuum...
Dave B
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coyoteboy
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| posted on 24/11/13 at 08:45 PM |
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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?
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Dave Bailey
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| posted on 24/11/13 at 08:54 PM |
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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
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coyoteboy
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| posted on 24/11/13 at 11:36 PM |
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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.
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Paul Turner
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| posted on 25/11/13 at 02:21 PM |
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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]
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