Help with oil leak, 72 LS5

[Mike E.]

There's a leak at the back of the block on my 72 LS5 4-speed coupe. I've cleaned everything, and when I start the car, it takes a couple of minutes, then a steady drip (every 5-8 seconds) comes from the bottom of the u-portion of the back of the pan and drips down the front face of the flywheel cover. The flywheel is dry. When I turn the car off, the dripping stops after the last few make their way down. I'm reasonably certain it is not coming from above (valve cover gasket, etc.) Previous owner may have tried to attack this, because there is a replacement GM oil pan on the car, the majority of bolts have been over-tightened, and orange silicone has been used everywhere along the pan gaskets. It looks like "if a little bit is good, a lot is much better." I just spent 3 hours removing orange silicone from the pan and the bottom of the block.
If I need to do a rear main bearing seal I will, but I would rather not if I don't. I don't want to overthink this, so am looking for someone with more experience than I to weigh in on this.
Thanks for your input. I have read extensively in the archives on this, but haven't seen identical symptoms in any other post.

[Jim T.]

Re: Help with oil leak, 72 LS5

Why are you apprehensive about changing the rear seal if you already have removed the oil pan?

[Patrick H.]

Re: Help with oil leak, 72 LS5

Why are you apprehensive about changing the rear seal if you already have removed the oil pan?

Agreed. You've got 90% or more of the job already done. Replacing the rear main seal is easy once you've got the pan off.
I'd worry more about straightening/flattening the pan and getting it right. You might also consider the Fel-Pro OS30061T for a pan gasket which is the one piece unit, as well as a Fel-Pro rear seal. I've had good luck with both of these.
Note that the pan gasket is a bit thicker than stock, and it's blue. If you're worried about color, you can paint the edge of the gasket orange before you install it... not that I'd know.

Other leak locations may be an oil galley plug on the rear of the block or else the transmission, however if this occurs even at rest then I'd doubt the trans.
Can you remove the flywheel cover and use a mirror to see where it's coming from?

Patrick

[Kevin G.]

Re: Help with oil leak, 72 LS5

Mike,

Just a thought but it not a small leak at the oil gauge line connection behind the distributor?

[Ed S.]

Re: Help with oil leak, 72 LS5

I have the exact same problem with a 1964 L76, engine oil dripping from the back of the engine after it has run a bit, continues to run for a short while after the engine is off. I have not yet removed the pan to perform repairs. When I do I intend to install a Fel Pro one piece gasket. The issue is, is there any way to determine if the leak is due to a bad pan gasket seal or a bad rear main seal (or both)? Note that my pan does not show any of the Bubba remedies that Mike indicated he found on his pan and block. I assume from the advice given to Mike that I should also replace the rear main seal since I will already have the pan off.

[Tom L.]

Re: Help with oil leak, 72 LS5

While I've never had this problem, and hope not to, I can't help but think that the plugs for the oil galleries in the rear of the block should be a consideration. Hey, ya never know... Good luck!!

[Domenic T.]

Re: Help with oil leak, 72 LS5

Mike,
Lots of good advice, especially What Patrick says about getting the pan surfaces flat again especially after you noticing the overtightened bolts. I always say start at the highest part where you see oil because oil does not drip up. One other possible place between the 2 oil plugs is the cam plug.
The rear main cap also needs a film of sealant. Sliding the top rear main seal in can shave the new seal and most come with a plastic protector to keep the sharp edge from shaving the rubber. Loosening the main bearing in front of the rear main gives you a few thousands more to work with. I have found that if you tighten the pan and let the gasket take a set for a few hours it will need to be tightened again and again not to exceed torque at any time.

Dom