1998 V70 high crankcase pressure episodes

[jimmy57]

Separate problem.

Wastegate is only active if boost gets high enough that it needs to allow exhaust gas to escape turbo exhaust housing incoming side to outlet side. This reduces gas volume spinning the turbo.

What does occur is that pressure in crankcase can burp oil backwards up through drain. The turbo exh seal ring is less effective when cold and the sealing system assumes a no pressure drain out of turbo. Pressure in drain can make a turbo with no issues pass oil.

Find out of there is ring leakage cold and fix that if found. Don't touch turbo until base engine is healthy.

[850GLT-NA]

I experienced the exact same problem (new PCV, used the bigger hose upgrade, slightly enlarged the PTC ports and thoroughly cleaned it), everything was fine for 5k miles, then it blew both rear cam seals.

There's suction @ the oil cap, and nothing out the dipstick. I replaced with 2 new cam seals, and they haven't popped since.

My theory: The car was parked outside for the first time overnight when this happened (-17C), and I assume the condensation in the oil trap may have frozen, temporarily restricting airflow, leading to blown seals.

Hasn't happened since being parked inside overnight.

Moral of the story: 1) My 850 does not like being parked outside 2) it does not like the cold.

[perkunas]

The PTC circuit should melt the ice, shouldn't it?
Edit: Sorry, it's the oil trap that was frozen, right

[erikv11]

OK so I checked the rings a bit just now. Unfortunately it has warmed up to 35 degrees today. I have a cheap-o leakdown tester from Harbor Freight that doesn't work right, the leakdown gauge is off so I can't check leakdown above 10 PSI, but I can use the tool to deliver compressed air to the cylinders.

I went down the line, 1 to 5, checked each cylinder at TDC. Two times (once on 3 and once on 5) the exhaust valves weren't closed all the way so I had to crank around to TDC again, but then it worked fine and the take-home is that all cylinders handled the 90 PSI air about the same: slight leakage out the oil cap, seemed about the same no all cylinders.

Does this mean they are all bad, or is this about normal? I can try to get a proper leakdown gauge (or fix the one I have?) if careful measurements are required here, but at first examination I don't think I am seeing bad rings?

Annnnd ... should I check for ring leakage again when it is colder? Should be down to 10 F this weekend.

Plus remember, I checked compression on the cold engine the other day and all cylinders came in at 175. They all leaked slowly there too, I thought that was normal for how stone cold the engine was. Or is that abnormal, and this engine has some above average ring wear?

[erikv11]

So maybe this one is solved. Many thanks for the suggestions.

I checked compression a few times when super cold, never saw any cylinder with substantial leakage. It isn't the PCV because I confirmed everything wide open after the last episode but before anything would have had a chance to thaw: once I reseated the cam seals I had an airtight seal, blowing back through the main PCV hose (the one to the PTC) would release pressure through the dipstick only when I pulled it, through the oil cap only when I opened it.

So I sent the turbo out for a rebuild, put it back in and have been driving it.

It's now been 500 miles with zero problems. Not a drop of oil in the bottom of the intercooler, what a difference!

If it gets really cold again this winter, that may be an important test, but it looks like indeed it was the turbo. I hope so. I'll update if I see any more episodes at all.

[jblackburn]

You know...mine tends to blow the cam seals on the timing belt side (annoying)...but this has happened a couple times in the recent past, and always when cold.

I was thinking perhaps ring problem with it as well, though the compression checks out well when warm (high 170's for me too). The turbo was out not too long ago and has minimal play, never *much* oil in the intercooler, but does lose some.

Erik, I'll stay subscribed...hope all is over for you.

[jblackburn]

Erik, actually...thinking through this some more, let me bounce this idea off you, since we may have something similar here. I just can't figure out how the turbo seals would cause the cam seals to blow out...while simultaneously dumping that amount of oil into the intake hoses (without doing it ALL the time!)

The oil trap is provided vacuum from the turbocharger area. We know what happens when the oil drain is blocked off - the air tube to the turbocharger begins huffing liquid oil from the oil trap, collecting in the intercooler hoses, throttle body, and causing exhaust smoke.

There are a series of baffles inside the oil trap that are soaked with condensation and oil. If it drops below freezing...those deposits freeze. PCV pressure is greatest at startup, before the cylinders/rings fully expand to fill the bore. Say this frozen condensation were to clog off the drain to the oil trap or a baffle. The car would quickly start pulling oil through that hose to the intake side of the turbo, which then pushes it through the air hoses into the intercooler. With nowhere for the positive pressure in the system to go, it finds the weakest point - we both know the rear cam seals are the most prone on these motors to blowing out - and POP!

When the engine warms up and melts any water vapor in the system...your problem disappears entirely like there were never crankcase pressure issues. If you recall...the 1994 models ran this huge tube up along the spark plug cover to try to warm the PCV gases (along with too many bends that just clogged) and 1999 models had a redesigned PCV system that ran coolant along with the PCV hoses under the intake manifold.

Another possibility...the freezing up of the vacuum tube for the PCV system (to the intake side of the turbocharger) causes the crankcase pressure to back up in the oil pan, sealing off the turbo oil drain tube. That oil then escapes past the turbo seals and is pumped through the intake system.

[erikv11]

I totally follow you here about the frozen PCV, and that is what I was originally assuming was wrong. But when I got in there, the intake side of the turbo had hardly any oil in it at all. The accordion tube was almost bone dry, just some white milky condensation. No (or very little) oil was coming in from the intake side on my car.

But on the other side there were buckets, there was oil everywhere. I thought Jimmy's comment was going to nail it, that is still the one I keep in the back of my mind: loose rings splurting oil into the turbo from the oil drain return line.

Your second point is a good one, had not thought of that in trying to sort this out. That could be checked - the instant it happens, pull the line and see if it is frozen.

Turbo seal could also be most susceptible when cold, I think it is a ring that looks/works like a piston ring?