waddisme

While doing some WOT runs to check on oil pressure, oil started dripping down the bottom of my block onto headers. As best as I can tell, it wasn't coming from oil cooler adapter or hoses or from heads. It seems to be coming out of the space between clutch cover somewhere. Does that mean a rear seal? My oil pressure was not increasing as my rpms were so I thought I had a restriction somewhere. I had plumbed my oil cooler lines with a union to bypass oil cooler to see if that was a restriction. While doing some WOT runs in 2nd gear, oil started running out the bottom. Did I mess something up?

CHJ In Virginia

Just bypassing the cooler will not cause any problems. You need to isolate the source of the leak. Use brake kleen all over the back of the engine and wipe down till dry. Run the engine and check carefully to find out where oil is coming from. It could be a valve cover gasket, oil cooler fitting / adapter, or a rear main seal Good luck in finding the source, these things can be an expensive PITA.

Han Solo

The first place I would check is the oil pressure sending unit. Then follow the gravity of the situation. Start looking high and forward and follow back and down.

waddisme

Didn't think about valve cover as I have recently repl those, but saw nothing below them, even after moving plug wires. Couldn't find my mirror, so I could get a good look at sending unit, although I could get my hand back there, and felt no oil. Will keep working my way down. Thanks.

varkwso

The answer is you have a leak...the pressure sending unit is under the rear of the intake. Check there.

froggy47

Not that this will help directly, but I did have a front engine seal leak at 50k miles. I think this is fairly common on engines with high rpm use.

I don't imagine that good ol GM put better seals on the back than the front.

Finally narrowed it down by cleaning (brake cleaner) and putting dye in the oil.

waddisme

Well, I finally got a mirror to look behind upper block. Didn't find any trace of oil. Oil pressure sensor area looked fine, valve covers looked fine and heads looked fine. From underneath with mirror, my oil cooler fittings and block adapter looked fine. The oil is pooling off the bolt above them. Same on the other side, oil has pooled on bottom of bolt above starter. Is rear seal all that is left to leak back there?

varkwso

I am pretty sure that is all you have left...

RedLS1GTO

Not sure if you did it when you put valve covers on it, but if not, heck your PCV...

I had a similar issue with a mystery leak that I couldn't track down. Sometimes the oil would be right where you described. I pulled the PCV and replaced it. Not a drop since. The old one was definitely gummed up.

95jersey

If you say back of the block and where the torque tube connects, I say 95% chance it is the main seal. This is a common problem, especially with C4's and C5's. My C5Z had a minor leak (just was always wet). I left it alone and it never got worse. Unfortunately a costly fix with a cheap part.

moespeeds

Clean it all up, then let it idle for 5 min and check for leaks. If no oil, run it hard for a min or two and check again. Main seal may not leak too much at idle, but should start flowing under load.

waddisme

Hauling it off to shop to get fixed. I hope the issues I have had with excess crankcase pressure is not the villain. Running the 3 valve cover ports to breather cans seems to have stopped oil from puking out top of motor, but I hope its not pushing out rear seal now.

froggy47

When my front main seal leaked, I thought excess crank case pressure & vented it. Still leaked. It was the crap GM seal.

waddisme

Well, I spent an hour cleaning up block to see exactly where the leak is coming from. Let it idle for about 5 mins and saw it dripping on floor. Crawled up under there, and the only place it is leaking is out of the clutch inspection plate. Could there be a oil pan block bolt above that or is it probably the rear seal?

varkwso

your rabbit died...sorry

froggy47

You can try the oil pan gasket, I did, in the end it's likely the cover. Can it wait until you need a clutch or guibo's?

RaleighSS

are you still on the stock internal LS6 ? I had oil pushing out my swanky short block.... soon after assembly ... it was coming from the rear cover seal ... I also had to vent both valve covers ... think my problem is solved now.

waddisme

Clutch has less than 10k mi and I repl guibos (incl 1 aluminum) 6 yrs ago with first clutch repl.

It is actually a forged LS2. I have the old style LS1 valve covers with 1 port on driver side and 2 ports on passenger side. I have all these tee'd together and dumping into breather can. I am hoping this set up is not what created the seal issue. The breather can is a smaller one that RX-Ben gave me. I think I may try a larger one that has a larger breather cap. It did not dump oil on top of motor at last track day and I did not notice it on bottom afterwards. It is off to the shop Wednesday.

Thanks for all the help though.

RaleighSS

any news on root cause ?

waddisme

Taking it to Heintz Racing next week to fix as they do all the hard work on my car. This is too big a job for me. I hope it is just a bad seal. Anyway, going to get them to repl pilot bearing also, as I have had 2 of those go bad, and install my Wilwood SL6s I just picked up for the front. I thought I would be doing Daytona in Dec but probably not now.