ibkevin

I posted a while back about a "howlling" under the hood and after pressing up the intake, the leak is in the charge air side under the intake. I want to rule out any simple fix that will keep me from having to pull the turbo for a third time in the past month.

Here's where it gets scary.

The leak is big enough to vent off the shop compressor's charge within a second or two, but does not create a vacuum leak big enough to keep the car from starting and running. Max boost has been about 5psi. After pressing up the intake several times, we noticed 5-6 drops of oil on the floor in neet lines parallel to both sides of the engine. I have noticed a small mystery oil drip starting on the drivers side at the back of the engine.

When I caped off the ISV lines the car would start but not hold idle.

I've read posts on changing AO seals..

951North

Please excuse my ignorance, "AO seal" ???

ibkevin

Air Oil Seperator.

I am scheduled to leave for Tahoe in the morning, either this is a simple fix or I gonna have a REALLY crappy weekend.

TRP951

Well without cutting the heatshield you have to pull the turbo to get to them. I cut my heat shield and wrapped the AOS with thermotec heat blanket.

ibkevin

That's a good alternative. I have a healthy chunk of the aluminized glass cloth to do the trick.

I think I'll put the intake back on, cap the AOS tap on the turbo inlet, and vent the crankcase to atmos. If nothing else this will be good for trouble shooting and let me get to Tahoe and back.

Thoughts??

Dal Heger

The air/oil separator is supposed to be on the intake side of the turbo, NOT the pressure side. There are only two lines off the pressure side of the turbo. 1- idle stabilizer valve, and 2- recirculation (blow-off) valve. Actually there is a third, that goes either to the venturi (early cars) then to the vacuum booster for the brake master cylinder, or directly to the one way valve on the brake master cylinder (late cars). If someone hooked up the positive crankcase vent line incorrectly (to the pressure side) then it would basically blow out the oil pan seal, and every other seal on the engine leading to massive leaks. It would also pop the dipstick out of the dipstick tube each time you hit boost.

If someone mixed up the two lines under the intake (switching the line that comes from the AOS and the idle stabilizer) then this would give you exactly the problem you are seeing. The AOS should be plugged into the intake boot (and can't be mixed up on a stock setup - it has a metal nipple that only fits into the rubber intake boot) and the Idle stabilizer should be attached to the intercooler pipe leading to the throttle body.

And everyone else is correct, to replace the AOS seals you have to basically remove the turrbo, the downpipe support bolts through one of the AOS mounts to the block.

Hope that helps.

Dal.

ibkevin

I just looked under the car, and there is a small amount of oil pooled on the block in front of the AOS, but behind it the block is dry.

This is a good sign?

Dal Heger

It's an irrelevant sign.

On a car with some miles, the rear plug on the balance shaft housings WILL leak, causing oil to pool right where you are looking.

Check the hoses. My bet is that they are hooked up incorrectly.

Dal.

ibkevin

I was hoping that was the cause of my problen too. I've done the venturi delete so my plumbing under the intake is pretty simple. The AOS is connected near the BOV.

ibkevin

Window cleaner sprayed on the upper seal and pressing the AOS vent line explain the whole story, I see another turbo/downpipe pulling next week.

Today's lesson learned, change those muthereffn' seals along with the balance shaft end cap seal, when you have the turbo out. As you do more and more work on an engine, it places greater stress on the weak links.

dougoh

just to let you know i replaced the upper rear balance shaft seal and aos seals with out pulling the turbo...it wasnt a big deal..i thought the worst when i searched this and kept putting it off ...i just started pulling the intake and everything up top then was able to get back out all the bolts on the balance shaft(i wasnt able to take them all out) ...then pryed the back cover out just enough to slide the seal out...whole thing took about 2 hrs.
hope that helps

Doug

Dal Heger

Where is the AOS connected??? It SHOULD be connected to the rubber intake boot going INTO the turbo, not on the hard pipe leading to the intake manifold. It should NEVER see pressure!

Just confirming. The BOV is connected to the hard pipe on the pressure side AND to the turbo intake.

The AOS should NEVER be pressurized, NEVER! It's only supposed to see vacuum.

Dal.

dougoh

i made that mistake and had leaks everywhere...no damage but i thought i was going crazy trying to figure how i had gotten all these leaks over night ...i switched the hoses back and everthing was fine...i only drove the car around the corner that way..

ibkevin

Dal, it's connected to the hardpipe between the MAF and turbo. Intake man has the brake boost, ISV, and Laust Manifold.

LOL! I will try to do seals without pulling the turbo/downpipe though.

The next question is.. venting AOS to atmosphere?

I did a quick read on some posts about excessive oil consumption, crank windage, case pressures, etc. I think I'll grab a generic pcv valve to install on the AOS line with some type of filter for the weekend.

Kinda seems like the turbo cars should have a pcv in this line anyway.

Dal Heger

Ok, cool, just trying to make sure.

Don't vent the AOS to the atmosphere, it needs the little bit of vacuum provided to make sure that there are no leaks. So a search and see what everyone else's experience is when venting to atmosphere.
The PCV is the AOS!

Keep it simple. The AOS is the only way to get vacuum in the crankcase, you want the crank to run at a bit of a vacuum all the time, putting a valve in the middle of that would be totally counterproductive.

If your rings are shot or your cylinder walls are gouged/scratched then you might be getting some great blow-by, but I'd highly doubt that it's enough to pressurize the crankcase and blow out seals. If it was producing that kind of blow-by then you'd know about it via other means.

The AOS seals (two o-rings) are tough to get to with a turbo. You NEED to take the downpipe off in order to remove the AOS. The downpipe is bolted through the AOS mount to the block. The oil might leak a little bit from that point, but it wouldn't be massive. The oil has to get up to that point, yes, even the lower hole is well above the oil level, and it's not a direct shot to the hole, so the oil won't splash up there either.

Good luck!

Dal.