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EFV-8 Club Forum / General Mercury Discussion / Leaking oil from back of motor on my 40 Mercury

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Posted By Discussion Topic: Leaking oil from back of motor on my 40 Mercury

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05-09-2020 @ 2:51 PM
Posts: 44
Joined: Nov 2009
Car has not been driven for about 6 years. Took it out of storage and drove it home and noticed oil spot on driveway after it was parked. Looks like the leak is at the rear of the oil pan. What is the best stop leak product to seal up the leak?

05-10-2020 @ 2:17 PM
Posts: 771
Joined: Oct 2009
how much oil on driveway? how much oil was/is in pan, remember these early engines are expected to leak a little as there is no real oil seal on the rear main but a lambryth seal which is just a series of slingers that supposedly funnel the oil back to the block. oh' old fords don't leak they just mark there territory!

05-11-2020 @ 7:01 AM
Posts: 6645
Joined: Oct 2009
I seriously doubt that there is any stop leak that will fix an oil pan drip on a flathead V-8.

Sometimes the front seal seeps and the oil runs to the back of the engine and then drips from the cotter pin. Other times just enough oil gets past the rear slinger and then drips from the cotter pin. If you have the later crankshaft with the "buss type" rope seal, you can pull the engine and replace the seals.


05-11-2020 @ 7:39 AM
Posts: 1607
Joined: Oct 2009
hi rradar
this is my take,
I suspect maybe from sitting, the rings have stuck causing internal pressure inside the engine, forcing the oil pass the rear main seal, also check your oil breather for being clogged,
I would drive the car, and use a little Marvel MYSTERY oil, in the gas, should free up the rings and valves,
if it did not leak before you let it sit, this maybe the cause,
better to do a few simple things, before you get really involved in something you do not need to do
I would also check the OIL PRESSURE SWITCH, on the back of engine, Have seen go bad,
also is you drive way on a incline ? parked the car up hill ,and how much oil on the dipstick, is it overfull ?
check on a flat surface, cold,
what color ?
hope this helps 37Ragtopman

This message was edited by 37RAGTOPMAN on 5-11-20 @ 8:20 AM

05-11-2020 @ 2:32 PM
Posts: 44
Joined: Nov 2009
Thanks for helpful info!! The oil spot on driveway is about 8" wide. I noticed a sort of trail of small spots leading up to the big spot. These smaller spots were about an inch wide and about 7"across from each other. I had also noticed oil spots on concrete floor where I kept the car stored. Seems like the problem must be in a place where oil is constantly in contact with 2 adjoining surfaces.

The motor sounds strong and starts right up. I did notice some clutch chatter when I drove home.

Can oil seep into the clutch assembly? .

Will Marvel Mystery Oil help seal up the front and rear main seals??

Would tightening up pan bolts help at all?

Not able to work on motors any more due to age and health issues

Thanks to all for suggestions.

05-11-2020 @ 6:11 PM
Posts: 1038
Joined: Mar 2013
Oil pan bolts require a very low torque; something like 6 lbs? If you over tighten them you can distort the pan and make a problem. Same with overhead valve covers. If the pan gasket is good, it won't leak; there is no pressure there to make it leak; only the crankshaft slinging the oil onto the sides of the pan.
"Back in the day"When I put pan or valve cover gaskets on, I used to tie them in stratigic places with thread to ensure that they didn't move while putting the pan, or cover in place. I did that on automatic transmission pans , oil pans, and valve covers and never had a leak! Valve covers that were leaking were distorted at the bolt holes from OVER TIGHTENING!!!

Regards, Steve Lee

07-19-2020 @ 6:23 AM
Posts: 1038
Joined: Mar 2013
Those oil pan bolts only take about 6 pounds of torque; Tightening them to tight can distort the flange on the oil pan and cause it to leak!! DON'T DO IT!!!!

I learned this from the old former mechanic, Percy, that became Service Mgr. at a Buick agency I worked for as a mechanic when I was about 32 years . He told me to tighten the Automatic transmission pan,after I installed a new gasket; to 6lbs.; I thought this pan is going to leak or fall off! It did neither!!

Regards, Steve Lee

07-27-2020 @ 3:39 PM
Posts: 771
Joined: Oct 2009
never over fill the engine, I know book says 5 quarts but use 4 1/2 qts. mark dipstick and maintain that level. see if the "cotter pin" is still in the pan drain hole and will swivel loosely, this pin is there for a reason-reason is to make sure the leaking oil gets out of the clutch housing, so Ford knew they would leak! if the pin was gone or the oil was overfull then that could make the normal leaking worse

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