Rear Main Seal Leak

rubio9800

Greasemonkey
Oct 10, 2020
145
28
California
Hey folks,

My 81GP is leaking, shop confirmed rear main seal, but was not comfortable in replacing as no guarantee it would stop the leak (rope type)

Definitely can’t do this on my own, has anyone dealt with this?

265 engine (just a weekend cruiser, not interested in high HP)

I recently switched to 15w40(synthetic), hoping it could slow it down. Would conventional be better in this case?

thanks
 
Last edited:

L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,500
113
West Michigan
Hey folks,

My 81GP is leaking, shop confirmed rear main seal, but was not comfortable in replacing as no guarantee it would stop the leak.

Definitely can’t do this on my own, has anyone dealt with this?

265 engine (just a weekend cruiser, not interested in high HP)

thanks
This is a very common problem on all older GM engines. It’s one of the reasons I upgraded to an LS engine.....My garage floor is dry.

The shop is correct. Replacing the seal will not guarantee the leak will be fixed but it should significantly reduce leakage if they do it right and use the right gaskets / seals.
 
  • Agree
Reactions: Rktpwrd

g0thiac

Master Mechanic
Sep 6, 2020
257
43
Hey folks,

My 81GP is leaking, shop confirmed rear main seal, but was not comfortable in replacing as no guarantee it would stop the leak (rope type)

Definitely can’t do this on my own, has anyone dealt with this?

265 engine (just a weekend cruiser, not interested in high HP)

I recently switched to 15w40, hoping it could slow it down.

thanks
Swap it out with a 305 or 350. 265's aren't worth rebuilding unless it has low mileage.
 

g0thiac

Master Mechanic
Sep 6, 2020
257
43
This is a very common problem on all older GM engines. It’s one of the reasons I upgraded to an LS engine.....My garage floor is dry.

The shop is correct. Replacing the seal will not guarantee the leak will be fixed but it should significantly reduce leakage if they do it right and use the right gaskets / seals.
He should go LS because he wants to do that, not because of a rear main leak. Because the money you'd spend on paying someone to swap the motor, computer and install the wiring out exceeds what a straight 350 swap would. Both my SBC's are over 30 years old, both over 150,000KM and have never had the seals worked on.
 

Jorge1958

Master Mechanic
Mar 2, 2019
342
43
Columbia City Oregon
U say your using 15w40 motor oil. I hope its not delo 400 or another diesel type oil. Very high detergent and can damage internal engine parts. Get a can of Lucas oil stop leak. Also 20w50 conventional motor oil. Try that. Should at least slow it down.
 
  • Like
Reactions: g0thiac

rubio9800

Greasemonkey
Thread starter
Oct 10, 2020
145
28
California
U say your using 15w40 motor oil. I hope its not delo 400 or another diesel type oil. Very high detergent and can damage internal engine parts. Get a can of Lucas oil stop leak. Also 20w50 conventional motor oil. Try that. Should at least slow it down.
rotella t6, yea it’s diesel.
i’ll try to do 20w50 today or tomorrow
 
  • Like
Reactions: g0thiac

g0thiac

Master Mechanic
Sep 6, 2020
257
43
it has 80k, i guess engine swap would be the only solution?
80,000KM or miles? You could rebuild it, but honestly the cost of a kit would be around the same of a 305 motor, if not 350 too with similar wear on it.
 

L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,500
113
West Michigan
He should go LS because he wants to do that, not because of a rear main leak. Because the money you'd spend on paying someone to swap the motor, computer and install the wiring out exceeds what a straight 350 swap would. Both my SBC's are over 30 years old, both over 150,000KM and have never had the seals worked on.
I’m not suggesting he swap an LS to fix the issue. The OP clearly stated he doesn’t need extra power and is happy with the performance of the anemic 265. I’m merely stating a fact that the older designs suck.
 

Similar threads

G-Body Performance Upgrades

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck ConsolesDixie Restoration DepotMike's MontesP-S-TSouthside Machine PerformanceUMI Performance

ContactAdmin@GBodyForum.comfor info on becoming a sponsor