Oil tank blowing oil, cracked ring?

[cstreit]

I experienced a LOT of oil being collected in the catch tank in the racecar this weekend. Almost a quart per 30 minute session.

I assume this is due to a cracked ring over-pressurizing the crankcase, but hope not. Any other theories on what might cause this?

1983 SC case based race engine... Oil tank vent goes to a catch tank/breather...

[jluetjen]

To ask the obvious - you did get the cylinders honed or roughened up before you installed new rings -- didn't you?

[cstreit]

John,

They were brand new Mahle's from the factory...

[911pcars]

Chris,
I supposed a compression test might indicate something abnormal. If not, is this something new or something you just discovered? It could be normal high speed blowby coupled with inadequate crankcase breathing volume. There are some threads in the archives on this subject. If all else looks normal you can always ....

..... use a quart and a half catch tank.

Sherwood

[cstreit]

Har har... problem is it'll continue to blow a quart even after the oil level is below the minimum mark....

[cstreit]

Oh, I also smelled some gas in my oil... Curiuoser and curiouser...

[911pcars]

Chris,
Hmmmm. Does it look like your oil level is ... + ?

I forget. Carbs or MFI? Do you get my drift?

Sherwood

[cstreit]

Oil level was at the bare minuimum mark at full temperature... Finding metal haze in the oil. Carbs...

[TimT]

Chris with the car hot and running open the oil filler, and see if there is steady vapor rising from the tank, or rythmic pulsing coming from the tank. Pulsing is a sign of worn or broken rings.

You could also have just overfilled the oil tank. I run my cars with the oil level on the low side..

Good luck!!

[cstreit]

Tim, there was steady vapor rising from the tank. Don't recall pulsing, but I didn't check. I may fill it with oil again and pull the breather hose off to see if I can feel pulsing from the motor vent... Then a compression test...

Just worried more about the metal haze in the oil still. Hoping it;s not a ring piece wearing away my new mahle cylinders!

THe oil was at or barely below minimum at "just off the track" temperatures... Couldn't get any slower safely.

[jluetjen]

Just some open thinking...

According to your other thread, you also had some oil pick-up problems. What might wear from a brief low oil pressure interval that would result in blowing oil? Alternatively, if the rings were still bedding in and there was a glitch of low oil pressure, would it wreck the ring(s)?

Are the two events related? (I hope not!)

[cstreit]

That;s what I'm concerend about John Let the analysis begin (in a few days)

I'll keep the board posted...

[jluetjen]

You might still want to run a quick compression test. If all of the cylinders are real low, maybe the rings haven't seated well. If one of them is much lower then the others, that's pretty obviously the problem.

[john walker's workshop]

proper length dipstick? there are a couple different ones, between early and late cars.

[cstreit]

JWW,

Good thought actually, sometimes the simplest explanations are the right ones!

I'm pretty sure the dipstick is close, only in that once the oil dropped below minimum, you could see fluctuation in the oil pressure guage, indicating that the pickup was pulling in air at IDLE.... So it was most certainly too low, to low for blowby, to low for engine operation, and still spewing oil into the tank...

So that being said, no matter what, I've gotta fix it because the engines emptying itself of oil to the point where it could be a hazard...

[john walker's workshop]

you shouldn't run out of oil pressure for just because the oil is at the lower mark on the stick. you would have to be a lot lower than that.

[cstreit]

JW,

I understand. Problem is, I am starting at the minimum mark on the dipstick. The engine then blows out several quarts of oil beneath that. Exactly how many I don't know, because it starts spewing out the vent in the catch tank once it's full...

So basically thats why the huge problem. On the track, the engine will empty itself of enough oil into the catch tank and everywhere else to start sucking air, even at idle.

[911pcars]

Hi Chris,
Can we back up? How are you plumbing the oil tank, catch tank and vent? Do you have any pics you could share?

Thanks,
Sherwood

[snowman]

Stop with all the crazy stuff already. Start with a compression check, then a leak down check, then talk to us.

[cstreit]

Sherwood, Jack,

Yes, that's my first move... Right now I'm outta town so I'm just collecting ideas and information, hence the nature of my posts... I'm not pulling anything apart untill I do a compression, leakdown, and some basic mechanical review.

If the compression and leakdown show a problem on one cylinder, I'll take it down, if they show nothing, I'll run it while keeping a very close eye on things and probably do an oil analysis no matter what.

Sherwood, I can post pics when I get back in town, but basically it's the classic setup of the 911 oil flow diagram.

1. The Oil pickup for the pump goes from the rear/bottom of the oil tank.
2. The oil cooler/external thermostat return is in the front/bottom of the tank.
3. The crankcase vent is plumbed to the front/top of the tank.
4. The Tank vent has a hose that rises 5" and then falls down to a 1.5 qt catch tank with breather element.