Pushing air out of valve cover @ idle

YZFR1 · 06-12-2012, 04:05 PM

Trying to figure out if this is responsible for the leaking oil pan on my brothers car. I hooked up an oil gauge today and the oil pressure is good. So then, i tried to unhook the breather tube on the valve cover while idling and it seems like it's pushing some air from there. When the engine is revved up, it's not pushing air anymore.

He has got a vented catch can setup on it (which i don't like) but i'm still confused as to why it's pushing air from the valve cover at idle but not when revved up?

Any insight would be very appreciated!

97mitzugst · 06-12-2012, 04:17 PM

Which breather are you talking about? The one on the side or the pcv on the back of the valve cover?

YZFR1 · 06-12-2012, 04:18 PM

The breather tube on the valve cover, not PCV valve

GSTurbo1 · 06-12-2012, 04:41 PM

I mean I don't know on my 420a when I had a bad valve cover gasket it shot oil in my engine compartment like a super soaker. So that leads me to think that as RPM's raise, the pressure on the breather should spike also. But that's just a guess, I mean logically it would make since to me.

WES_393 · 06-12-2012, 04:52 PM

That's pretty normal. At idle there is some blow-by, but when you rev the engine it pulls enough air to evacuate the crankcase. So long as the air coming out at idle isn't blue smoke, you (or your brother) should be just fine. High crankcase pressure usually makes the oil cap, valve cover, dipstick, etc leak oil long before the pan ever would. I suggest dropping the pan and resealing it if the leak is bad. It only takes about an hour or so to drop the pan.

PieEyedPiper · 06-12-2012, 05:26 PM

I would imagine that the pulses are just that much more noticeable (spaced out) at idle and that there is still pressure in the VC/CC at higher rpms. Would be awfully nice though, to have no CC pressure build up at high rpm.

YZFR1 · 06-13-2012, 07:56 AM

The oil pan has already been pulled twice, the first time i resealed it with a homemade gasket w/copper spray and it leaked a little, then i re-did it with black rtv and it leaked a lot. I'm more than positive that something has got to be causing this.

Quote:

Originally Posted by WES_393

That's pretty normal. At idle there is some blow-by, but when you rev the engine it pulls enough air to evacuate the crankcase.

That just doesn't seem right to me. I got this quote from Calan's 4g63 PCV System article: "Under maximum intake vacuum (such as when idling or decelerating) the amount of blow by in the engine is at it’s minimum"

Calan · 06-13-2012, 08:36 AM

Quote:

Originally Posted by YZFR1

I got this quote from Calan's 4g63 PCV System article: "Under maximum intake vacuum (such as when idling or decelerating) the amount of blow by in the engine is at it’s minimum"

Quote:

Originally Posted by WES_393

That's pretty normal. At idle there is some blow-by, but when you rev the engine it pulls enough air to evacuate the crankcase. So long as the air coming out at idle isn't blue smoke, you (or your brother) should be just fine. High crankcase pressure usually makes the oil cap, valve cover, dipstick, etc leak oil long before the pan ever would. I suggest dropping the pan and resealing it if the leak is bad. It only takes about an hour or so to drop the pan.

Wes is dead on here.

There is a difference between air flow, and air pressure. It's normal for air to be blowing around in the VC during off-boost; that is the whole point of the "ventilation" aspect of the PCV system. Air gets drawn into the VC and circulated to ventilate the crankcase.

Even with only a breather on the VC, you'll still most likely notice some air blowing around. As long as this air can flow freely without restrictions, it's all good. It's only a problem when something is restricting the flow (clogged PCV valve, etc) and pressure rises. Some engines can flow an incredible amount of air through the crankcase, and still don't have excessive pressure problems because they are well ventilated.

Sounds like your brother just has a leaking oil pan. It happens.

YZFR1 · 06-13-2012, 08:49 AM

^^Ok, thanks for your response!

Honestly, i'm not sure if he even has a PCV valve on his car. The way it's set up is that both tubes from the valve cover go to a vented catch can. That's why i was confused, since his intake manifold and valve cover are not connected in any way.

I guess, i will try and re-do the oil pan again with grey rtv.

Calan · 06-13-2012, 09:12 AM

Quote:

Originally Posted by YZFR1

Honestly, i'm not sure if he even has a PCV valve on his car. The way it's set up is that both tubes from the valve cover go to a vented catch can.

If those lines are still using the factory PCV valve and breather ports, he probably does have CC pressure issues during boost...in addition to the leaking oil pan.

If you run an open can, you need some pretty good sized lines to overcome the pressure drop across the breather and other restrictions (and even then you will always have at least some amount of positive pressure). A couple of -10ANs is about ideal; two 8ANs would be the minimum I would suggest.

With a closed system and a negative pressure source (turbo inlet), you can get away with much smaller lines.

YZFR1 · 06-13-2012, 09:26 AM

Yeah, i've been wanting to re-do his pcv system since the day i picked the car up for him. Thanks again!