I don’t believe it’s possible to have a rear main seal not leak

[dn010]

Or, another cause is when the seal creates a groove in your crankshaft surface which will cause a leak even with a new seal being installed over it. I found that after some measuring where the groove is and installing the seal either further in or out of the carrier depending on that measurement will make the seal miss the groove. I did this on my original 77KMI engine that had a groove in the crank every time I had the transmission out and it never leaked. My current engine doesn't leak however it is an EFI B280F. I have not looked into speedi-sleeves but that's another possibility.

[BladeBronson]

Hrmm, I dunno. I had my rear main replaced maybe 2 years ago by Rob Grady. The car doesn't sit and is driven regularly. The engine is a Stage II, done in 2007, and didn't have a leak when I bought it 5 years ago. My first car was not a Stage II and had 3 or 4 rear mains replaced in the 5 years that I owned it - either by Don/Danny or random mechanics in the bay area.

I found this product with good reviews, but I hesitate to pour anything in when I don't know exactly what it does: https://www.amazon.com/BlueDevil-Rea.../dp/B0079JX4JO

[dn010]

I don’t know this product but am always hesitant of a miracle in a bottle unless it’s a last resort.

[Ron]

Throw a vacuum gauge on the crankcase...

=====

The crankcase ventilation system works BUT, only up to a point. If you have large air leaks or are getting excessive blow-by it will not be able to handle it. The 'fix" is not to improve the ventilation system, the fix is to find and fix the leaks or the cause for the excessive blow-by. On one car that had a turbo system, it got over-boosted and cracked the pistons. That car had so much blow-by, when you got into boost it would blow the oil cap right off and spew oil out. An extreme example. Point is, if everything is working correctly the crankcase ventilation system should keep the crankcase slightly negative preventing oil leaks. A major cause for that rear seal to leak IMHO is that at some point many Deloreans sat and did not run. That causes the seals to get a 'set" and once you start running the motor again, the seal leaks. Other possible causes include using the wrong type of oil (synthetic will leak if an old car is suddenly changed to syn) or too much oil.

+1

Generally, I don't like using NOS seals. Like the "set" and worn-out ones, they don't compensate for wear.
Double Lip-


If the crank doesn't need a sleeve/repaired, the seal could of been damaged during installation/other repairs, installed without lubing it to prevent dry-lip, or ?? The old ones should tell the story there. Contaminants, and dirt, especially with excess thrust washer clearance, should leave signs.

Throw a good vacuum gauge on the crankcase...

[David T]

Actually you don't even need a gauge. An old "trick" to see if things are working. Take a flat, stiff piece of paper and place it over the oil fill while the motor is running. It should stick to it and stay in place if the crankcase is "negative". Whenever you install a new seal you always check the shaft for grooves, scratches, or any other damage. If it is minor you can polish it out, if it is more than that you either reposition the seal a bit if you can, or use a Speedi-Sleeve.

[Ron]

Hrmm, I dunno. I had my rear main replaced maybe 2 years ago by Rob Grady. The car doesn't sit and is driven regularly. The engine is a Stage II, done in 2007, and didn't have a leak when I bought it 5 years ago. My first car was not a Stage II and had 3 or 4 rear mains replaced in the 5 years that I owned it - either by Don/Danny or random mechanics in the bay area.

I found this product with good reviews, but I hesitate to pour anything in when I don't know exactly what it does: https://www.amazon.com/BlueDevil-Rea.../dp/B0079JX4JO

I don’t know this product but am always hesitant of a miracle in a bottle unless it’s a last resort.

Me either. But I have seen several similar ones for decades. They usually make the seal swell chemically. If it works, at all, the seal will wear out in soon... BS.

However, I tried the Blue Devil Pour-N-Go Head Gasket/Block Sealer twice on bets (against it). $50 unconditional guarantee (If you agree to try a delivered 2nd bottle free, if the 1st one does not fix it)! Months later, I'm 0 for 2 and down a toddy or two but they both shared...

If it is a last resort and I were to try one, I would definitely try this one for the heck of it.

P.S. The mechanics should report what they find during replacement(s)..

[Ron]

Actually you don't even need a gauge. An old "trick" to see if things are working. Take a flat, stiff piece of paper and place it over the oil fill while the motor is running. It should stick to it and stay in place if tMy dog he crankcase is "negative". Whenever you install a new seal you always check the shaft for grooves, scratches, or any other damage. If it is minor you can polish it out, if it is more than that you either reposition the seal a bit if you can, or use a Speedi-Sleeve.

Agreed. You don't even need that if all you want to know if it is going negative...my dog uses the palm of his hand

I like a true double lip seal best because you usually get at least one on a good surface and the positioning of the other has a fair chance too, extra. With all of the repeated failures, I would guess it's a pressure problem(s) and would want to know how much it is dealing with exactly (not being privy to the full history etc.)

[FABombjoy]

The paper test is only going to work on cars that don't have the entire PCV system built in to the oil cap.

On a B28F, if you remove the oil cap you will only find positive pressure at the fill port unless the engine is off

[David T]

The stuff that is sold to stop seal leaks does swell the seals. And it does work. For a while. What then happens, the seal hardens and leaks a LOT more. Very temporary fix. Some of the stuff sold to fix leaky head gaskets also works, at least long enough to get through inspection or sell the car! There is no "Magic in a bottle". What I can say works is Techron to clean injectors, Barr's Stop leak for small coolant leaks, and Marvel Mystery Oil for break-in oil changes. Some of the stuff sold to flush and clean an engine when doing oil changes also work. I have become very skeptical about stuff in bottles that claim to fix things. If they work at all they work very temporarily and cause more damage.

[FABombjoy]

This was posted to one of the FB restoration groups a while back. I'd say it was pretty much a cork at this point.

Clean your "flame arrestor"

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