OK...I'm hoping someone might be able to help me out with a question. I had assumed (base dupon locaiton) for some time that I have had a rear main seal leak. I jst swapped trasnmissions, and it appears that it is possible that the leak is actually coming from the rear seal where the oil pan meets the block. How can I tell for sure?

I have the car on jack stands (fo the tranny swap), so the engine is "tilted" back, and it is leaking quite a bit...the engine has not run in a couple of months.

Will the rear main seal leak if the engine has not been run?

Or do you think I have a rear main seal leak?

You have to make sure by visual inspection everything above the crankshaft is dry, e.g., valve covers, intake manifold, oil pressure sender, and block sealing plug on the driver side where the drvr cyl head partially covers, a Welch plug, about 1/3-1/2 the way down the deck at the rear from the intake manifold. With the engine at a tilt, oil in the top cyl head flows back to the back of the valve cover and could drain out the corners.

Often when a block is hot tanked for cleaning, this plug gets eroded away and usually not changed. Only way to change it is to pull the head and replace the plug. However, this may be a mute point, but still need to inspect just to be sure.

Rear seal leaking is common and the foward surface of the flywheel would be wet with oil. Could be the rear camshaft plug leaking as well as the oil pan gasket. Hard to distinguish between an oil pan gasket and rear seal. An older rear seal leaks when there is no pressure developed; the oil pressure pushes the lip against the crankshaft and no leak occurs. Stop the engine and tension on the lip is relieved, oil leaks out.

You have to make sure by visual inspection everything above the crankshaft is dry, e.g., valve covers, intake manifold, oil pressure sender, and block sealing plug on the driver side where the drvr cyl head partially covers, a Welch plug, about 1/3-1/2 the way down the deck at the rear from the intake manifold. With the engine at a tilt, oil in the top cyl head flows back to the back of the valve cover and could drain out the corners.

Often when a block is hot tanked for cleaning, this plug gets eroded away and usually not changed. Only way to change it is to pull the head and replace the plug. However, this may be a mute point, but still need to inspect just to be sure.

Rear seal leaking is common and the foward surface of the flywheel would be wet with oil. Could be the rear camshaft plug leaking as well as the oil pan gasket. Hard to distinguish between an oil pan gasket and rear seal. An older rear seal leaks when there is no pressure developed; the oil pressure pushes the lip against the crankshaft and no leak occurs. Stop the engine and tension on the lip is relieved, oil leaks out.


The leak i sdefinitely not coming fomr the top of the block, or the plug that yous mentioned...it is definitly either the rear main or the oil pan (after market 7 QT pan)...I just hate to mess with the rear main seal if that is not even the problem...bu the crank flange really prevents any "close-up" investigation of the leak...

Clean everything off with BraKleen® and with a powerful light, look while the engine is running with a dentist mirror.

Something that I chased for a while, was an oil pan gasket leak (one piece), where oil was actually seaping past between main bearing cap and gasket. Since applying RTV (instructions say its not necessary) the leak stopped.

On the rear main seal, I am using the premium blue viton ( I believe) , with sealer on the ends and at the main cap edges with the seal split ends, being clocked about 1/4" off the main cap parting line.

Hope this helps.