I've had some persistent oil leak /blowby problems at the track lately recently. First time, I had severe blowby issues and the car was leaking from what looked like the turbo return. I filled my catch can in 2 sessions. My valve cover vent was vented to atmosphere at the time (through the catch can) so I thought routing it to the turbo inlet would solve it. I also added a kynar check valve to the PCV side along with my 323 GTX PCV valve and a catch can in between just to be sure.

Second time I found leaks coming off the end of my splitter after about 5 sessions. Looks like return line again. Catch can was full again. So it seems providing a vacuum source for the vent helped the problem slightly but didn't solve it. Oil return shouldn't leak easily because it's supposed to be a low pressure line. But if it's seeing pressure from the oil pan that could cause problems.

So, looks like excess crankcase pressure is the culprit. It's not coming from the intake manifold...so my motor's probably broken somewhere. Now the question is, bad head or bad piston/rings? I do know that my head isn't the best. Here are the leakdown numbers from the last year (last time the car was really driven hard):
Compression numbers:
162, 160, 160, 160

Leakdown numbers:
5%, 17%, 16%, 7%

mechanic said probably exhaust side valves

Car doesn't smoke or anything. Maybe a little white smoke on startup. Still runs very strong. Can bad valves allow pressure to get into the crankcase? And if I had bad rings wouldn't I be blowing smoke out the back all the time?

Car info:
323 GTX block @ 12 psi
99 head
2560R
EMS4

For ref, car was tuned by Savington so there shouldn't be any probs with the tune. Though it was overboosting for a while after I took it home from the dyno. I went into the cal and reduced the boost target but it still spikes, but at least in the safe range that it was tuned for.

Or maybe I'm completely off track, but I'm kinda out of ideas. This constant oil leak blowby problem is driving me nuts! Help appreciated!

 

THats a lot of leakdown on the middle 2 cylinders. Where was the air coming out during the leak down test?

 

First thing I'd check are the valve seals. Known failure point.

 

In my experience, if you've got a lot of blowby because of broken rings, your oil will turn black quickly. Is your oil color normal?

 

The oil in my catchcan was dark, but on the dipstick it's still looking pretty new after the track day.

 

he said it sounded like exhaust side

Oh interesting, would valve seals allow pressure to leak into crankcase?

 

Um, yes. A couple ways you get pressure in the crankcase: blow-by from the rings or exhaust/boost pushing past the valve guides and valve stem seals. The pressure from around the stem seals will end up underneath the valve cover, essentially inside the crankcase as that's how its all connected.

I don't mean to be a dick or nothin' but have you spent much time inside an engine?

 

That's pretty much it - rings and/or valve seals - likely both if a worn motor. The exhaust side valve seals will cook hard with time.

 

No offense taken! I'm from rotary idiot land where we know nothing about piston engines. I'm learning though haha.


But yea I guess valve seals seem likely. I get some whispy white smoke out the valve cover sometimes when I open the oil filler cap.

Whats a good way to check valve seals?

 

Does it smoke briefly when abruptly letting off the gas, after a WOT sprint?

 

I don't know that valve stem seals would be my first suspicion; they're primarily there to keep oil from being sucked down the valve stem when the cylinder is in the intake stroke (pulling a vacuum). In my experience, visible oil smoke from the tailpipe is usually the most obvious symptom. It's more likely either wear in the valve/seat area, or a worn guide which allows the valve stem to **** slightly and consequently, allow misalignment and leakage at the seat.

The most obvious course of action is to just go ahead and pull the top end and take the head to be pressure tested. It's likely either a bad guide or cracked seat in the head, a failed head gasket, or something obviously wrong in one of the cylinder bores.

Pull the head. It takes like an hour with air tools.

 

Also, no need to remove the manifolds to pull the head. In fact, they make good handles. JP method.

 

I haven't checked this. I'll need to find a buddy to drive behind me. I can't see anything in the rear view. I started it today after a week of sitting. It's just barely barely smoking. I can't see it unless I crouch right next to it and stare at it from the right angle.
After it's warm I have not been able to get it to smoke. I revved it to 6500 for like 4 seconds and let off. My brother was standing next to the exhaust couldn't see anything. Also did a engine braking in first and parked. Nothing.

Yea I guess it's time to pull the head. I mean we already know that I have and large leakage so something is wrong.

Lol good tip

 

Ok so I got a friend to follow me. I ran the WOT test and a engine braking down a giant hill in 2nd gear test. I couldn't get it to smoke under any circumstances.

I attempted a leakdown test with a harbor freight tester and got some ridiculous numbers.

18%
25%
21%
16%

Now I don't know if I believe these numbers but it could be possible I guess. This tester did confuse me quite a bit so I don't even know if I did it right.

Oil still looks clean, one track day and about 1k miles on the oil.

Not sure what to do :(.

 

Rebuild? I have a similar situation, car burns oil like a mofukka, 1 quart every 1k or less when driven hard, which it always is. Leakdown for my car were as follows:

5% rings only
15% rings + leaky exhaust valve
20% rings + leaky exhaust valve
10% rings only

catch can is 1/4 full after a few k miles, so blowby itself doesn't seem that bad. Maybe valve stem seals like others were saying, and maybe this turbo that has been making funny noises. Or rings, idk.

So kind of similar to yours. I have no idea what is sucking up oil, so my solution right now is to tear it down and replace everything. Undergoing a bottom end rebuild and upgrading the rods now, going to completely refresh the head, and I'm going with a bigger turbo too. That should hit all the bases

 

Forget valve seals. Those leakdown numbers tell the tale of a tired motor. You may get lucky with just a valve job. The only way to know is to swap heads with a rebuild one. Even then I doubt that's where the oil is coming from. That is likely tired rings.

 

My pro motor builder guy was talking about a reformulation of "over the counter" motor oils a few months ago that have resulted in a shitpot of wiped cam and worn ring jobs for him. If you were marginal before, the wear may have accelerated with the reformulation of consumer oils...

 

That's why I've switched to the Diesel formulations on all my flat tappet cars. But, I hear wear inhibitors (phosphorus, zinc) are being reduced in the Diesel oils too. Grrrrrr . . . .

The 20 weight oils in new cars are a joke. EPA hates cars.

Just my opinion, mind you.

 

I think its probably pretty well documented at this point. CAFE is a BITCH and I refuse to use 0/5w20 in anything.

I used to use the old formulation Delo 400 in EVERYTHING from a Chevy 454 propane fired generator to the John Deere 710 backhoe and everything in between when I was working as a caretaker on a very remote piece of property. Everything ran perfectly for years until I left and the new guy started using newer oils in everything. They killed 3 of the generators I had lovingly maintained for nearly a decade in a matter of a year. The mechanic who did the post-mortum said the same thing: This new oil is ****. Use something formulated for Diesel or GTFO. I got the same warning from the oldschool machinist who redid the heads on my 70's era FE powered F-250: Use a zinc additive or use diesel specific oils or expect to replace the cam and lifters in a couple years. Bah!

</rant>

OP needs an engine refresh

 

The real reason oils suck it these days is because the zinc/phosphorus kills cats. Since the feds now require OEM's to warranty cats for 10years or 100k miles the #1 priority of OEM's is saving the cats. They are the ones who spec oil so there you go. Look for race oils like brad penn, redline or swepco. All of those will protect your motor well.

For more reading on the subject.... Oils: What motor oil should I use? Which oil is best for my Porsche or aircooled engine?