Where is my Oil Leak?

[Patrick H.]

All,

As many of you know I have a 71 350/270 L-48 4 speed. Ever since it was rebuilt 3 years ago I have been chasing oil leak(s). To date, I have fixed the small ones from the distributor, the oil pressure line, and (finally) the valve covers. I still have one that puzzles me, however (at least a little).

My engine continues to have oil on the REAR surface of the oil pan, and on the FRONT surface of the clutch inspection cover. There is NO oil within the clutch or on the inner surface of the inspection cover. It is dry as a bone there. The oil then goes back across the bellhousing, onto the trans, etc thanks to airflow as I drive along.

My question is this: is it the rear of the oil pan gasket that leaks, is it the rear bearing seal that leaks, or might I have a totally different gremlin? I know that to fix either requires removal of the oil pan, but I would like to know what I'm in for before I start. And yes, I actually watched my engine as it was assembled, and I know the rear seal is not in backwards. :)

Thanks for any assistance you can give.

Patrick

[Trebor M #25911]

Re: Where is my Oil Leak?

Patrick

There could be a couple of suspect areas of weepage.

1) The 3 allen head plugs around the rear cam stop are loose.

2) rear seal is torn.

3)pan gasket leak.

4) accessive crankcase presure.

To have the leak directly in center of rear pan and leak enough to coat under carriage severly I would say it is one of the 4 I mentioned. Dropping the pan on a corvette is not a hard job. The only interference is the center link. Make sure that all leaks from above have been eliminated. Good luck

[Trebor M #25911]

Re: Where is my Oil Leak?

Patrick

There could be a couple of suspect areas of weepage.

1) The 3 allen head plugs around the rear cam stop are loose.

2) rear seal is torn.

3)pan gasket leak.

4) accessive crankcase presure.

To have the leak directly in center of rear pan and leak enough to coat under carriage severly I would say it is one of the 4 I mentioned. Dropping the pan on a corvette is not a hard job. The only interference is the center link. Make sure that all leaks from above have been eliminated. Good luck

[Jack H.]

Re: Where is my Oil Leak?

In addition, that's a 'natural' place for oil to 'pool'. Leaks higher on the block will follow gravity down and airflow will migrate them back. Suggest with all the other due diligence you've done, a good thing to do (if you haven't already) is put car on lift, and steam clean the entire engine down to Chevy orange, then watch to see if oil continues to show up there vs. prior leaks 'moving'....

[Jack H.]

Re: Where is my Oil Leak?

In addition, that's a 'natural' place for oil to 'pool'. Leaks higher on the block will follow gravity down and airflow will migrate them back. Suggest with all the other due diligence you've done, a good thing to do (if you haven't already) is put car on lift, and steam clean the entire engine down to Chevy orange, then watch to see if oil continues to show up there vs. prior leaks 'moving'....

[Chuck G.]

Re: Where is my Oil Leak?

Hi Patrick; One of the biggest "leak" areas in small block Chevy engines is the rear of the intake manifold....usually at one or both of the small "V's" where the heads meet the block. It could be dripping down from there. Hope this helps. Chuck

[Chuck G.]

Re: Where is my Oil Leak?

Hi Patrick; One of the biggest "leak" areas in small block Chevy engines is the rear of the intake manifold....usually at one or both of the small "V's" where the heads meet the block. It could be dripping down from there. Hope this helps. Chuck

[Patrick H.]

Re: Where is my Oil Leak?

Jack,

Steam clean a Corvette motor??? Haven't you ever read "How to Detail a Corvette" by Antonick? He considers this a huge no-no due to the loss of original marks with this method. :)

Anyway, it was, as noted, rebuilt 3 years ago and I make pains to keep it clean. That's half the reason I want to delete the leak.

Patrick

[Patrick H.]

Re: Where is my Oil Leak?

Jack,

Steam clean a Corvette motor??? Haven't you ever read "How to Detail a Corvette" by Antonick? He considers this a huge no-no due to the loss of original marks with this method. :)

Anyway, it was, as noted, rebuilt 3 years ago and I make pains to keep it clean. That's half the reason I want to delete the leak.

Patrick

[corvgreg]

Re: Where is my Oil Leak?

Check the front of your engine next to the fuel pump. There are two threaded holes, and the top one usually goes all the wall through to the fuel pump cavity. This allows you to put a bolt in to secure the pushrod while you're installing the fuel pump. Oil will weep out of this hole and be sprayed back onto your pan and clutch inspection cover.

[corvgreg]

Re: Where is my Oil Leak?

Check the front of your engine next to the fuel pump. There are two threaded holes, and the top one usually goes all the wall through to the fuel pump cavity. This allows you to put a bolt in to secure the pushrod while you're installing the fuel pump. Oil will weep out of this hole and be sprayed back onto your pan and clutch inspection cover.

[Rich Mullikin]

Re: Where is my Oil Leak?

Pat,

Although most of the responses are potentially valid places for you to start looking, Chuck has given you an area that is over looked by many. My '69 big block gave me similar problems for a long time. It drove me crazy! I tried replacing distributor gasket, valve cover gaskets, oil pan gasket without any success. My problem was a leaking intake manifold gasket. It was located on the left side (rear) where the intake, head and block meet. It was a very small leak but after a few hundred miles, what a mess. I could never keep the bell housing clean. This past winter I pulled the motor to detail the engine compartment and while I had the engine out I fixed the leak. I had talked to a few mechanics who recommended that when I put the new gaskets in to eliminate the rubber or cork end gaskets. Instead put a nice thick bead of silicone down the head, across the block and up the other head. I did this front and rear and the leak is gone. Engine compartment looks better than ever and most important I got to take up that nasty cat litter I had to keep under the car.

This might not be your problem, but I would sure check it out.

Rich

[Rich Mullikin]

Re: Where is my Oil Leak?

Pat,

Although most of the responses are potentially valid places for you to start looking, Chuck has given you an area that is over looked by many. My '69 big block gave me similar problems for a long time. It drove me crazy! I tried replacing distributor gasket, valve cover gaskets, oil pan gasket without any success. My problem was a leaking intake manifold gasket. It was located on the left side (rear) where the intake, head and block meet. It was a very small leak but after a few hundred miles, what a mess. I could never keep the bell housing clean. This past winter I pulled the motor to detail the engine compartment and while I had the engine out I fixed the leak. I had talked to a few mechanics who recommended that when I put the new gaskets in to eliminate the rubber or cork end gaskets. Instead put a nice thick bead of silicone down the head, across the block and up the other head. I did this front and rear and the leak is gone. Engine compartment looks better than ever and most important I got to take up that nasty cat litter I had to keep under the car.

This might not be your problem, but I would sure check it out.

Rich

[Patrick H.]

Re: Where is my Oil Leak?

Already have a bolt in there blocking the hole...

Patrick

[Patrick H.]

Re: Where is my Oil Leak?

Already have a bolt in there blocking the hole...

Patrick