Blue Devil Oil Stop Leak Vs Rear Main Seal

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1. Looks like the rear main seal on my 225 slant is bad, and my understanding is that the engine must be removed to fix it. YouTube has a number of videos of guys using Blue Devil rear main seal stop leak, and most reviews are pretty good. Has anyone on this forum ever used this stuff on a slant six? Did it work? For how long? Will it screw up your engine in the long run? Any and all please weigh in with your opinion. Slant Six Dan, if you're out there, what do you think? If you listen to the YouTube reviews, the stuff seems like a miracle cure - almost too good to be true. Thoughts anyone?

2. 

   toolmanmike Moderator Staff Member FABO Gold Member

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   Page @slantsixdan this way. A little hocus pocus in a can? Old brake fluid will swell rubber seals. Is the slant 6 rear main a rope?

3. I don't know if it's a rope seal or not, as I've never actually seen it.

5. if it is a rubber seal, brake fluid will work as toolmanmike says, BUT, it is only temporary. it will start leaking big time at the worst possible moment. PS, it also will swell the seals in an automatic, but again, when it goes bad.....

6. I just replaced the rear main in my 360 in the car, it was a two piece seal. Can the same be done on a slant?

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   RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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   The Blue Devil stuff is top notch additive. It does not swell seals like the old stuff.

12. 

    Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

    According to rock auto the 65 225 rear crank seal is a 2 piece rubber.

    Now that does not mean that the OEM seal wasn't rope.

13. My engine is a 1976 replacement block, rebuilt at some time before I bought the car.

14. Is it a permanent fix? Do you think it will mess up the inside of my engine? Thanks.

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    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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    I guess it depends on how bad the leak is. If it stops it and it stays stopped, yeah, I'd call that permanent. The Lucas and Blue Devil stuff both only soften seals but do not dissolve and swell them over time like some of the older stuff. And no, it will not hurt your engine. I am running some of the Blue Devil general oil stop leak in Kitty's car now. It has a main bearing girdle that bolts to the bottom of the block that holds the crank in. It's sammiched between the block and the oil pan. They used a rubber o-ring style gasket for the oil pan side and that Ford grey sealer on the block side. It's a common problem on the 3.0 for the sealer to fail......and ours has. The engine has to be removed to repair it. I'm not ready for all that right now. The only one drawback is you must add the stop leak back when you do an oil change.

17. Try it. If it doesn't work, you can change the seal from below fairly easily, once you get the oil pan off which is the hard part. You will need a Pitman arm puller to unbolt the steering link from the gearbox and move it down. You will likely need to unbolt both engine mounts to jack the engine up 2" above the K-frame, then prop it there w/ wood blocks under the mounts. That gives room to get at the front oil pan bolts and work the pan out. You might need to rotate the crank so #1 piston is up so the pan doesn't hit the crank arm.

    The seal is on a separate aluminum holder behind the aft main bearing cap. Check that the tapped holes for the oil pan weren't stripped by a prior gomer mechanic (common) since now is the time to fix that w/ a Helicoil. In my 1964 Slant, the seal was a 2-piece rubber, but likely had been swapped. Same PN for 426 Hemi engines. If the rubber is old and cracks easy, that would explain why the Blue Devil didn't work.

    Change the oil pan gasket. I used a permanent silicone gasket from Real Gaskets of TN. While in-there, I suggest removing a rod cap to check the bearing. If any wear or scoring, I would change all. Do one at a time so you don't mix them up and stamp for orientation if no factory marks (forget). Also remove a main bearing cap to check for wear. In the several Mopar engines I've done, the rod bearings needed changing, but main bearings were perfect. You must use a torque wrench to retighten the bearing caps.

    Of course, before all this, check compression. If <110 psig in any cylinder, I would consider a rebuild (over-bore & new pistons or at least a factory hone and ring job). To do best, the block needs to come out. But, before that, have a mechanic you trust verify since easy to get a bad reading. Also, do a leak-down test to find if rings or valves. Plus, a sanity check by turning the engine over by hand and feeling for strong resistance from each cylinder (3 per rotation), taking >2 sec for the pressure to leak down. If so, the engine is fine and your compression test is faulty.

18. Blue devil was used on a 2003 4x4 transfer case with 200,000 miles on it. New synthetic oil had just been added for that mileage service and the rear seal started leaking almost instantly. Weird!
    Puddling was small but very noticeable after the vehicle sat overnight. For a few weeks the driveway needed to be cleaned every day. Being a Toyota it was an 18 hour job according to the time rate book. The transmission shop, really not wanting to do it mainly because of how much it was going to cost me, suggested trying Blue Devil. After reading the instructions the proper amount was added and the recommended 100 mile round trip was driven. I thought maybe the synthetic oil, being new, was just too slick for the seal to hold and I didn't have high hopes. It was a shocking miracle that there wasn't another drop leaked. Oh, a question Are you using synthetic motor oil?
    

19. That is because the two piece rubber seal is backwards compatible and is used to service the rope seals. It is possible to find NOS rope seals, but the two piece rubber seal is a superior sealing solution.

    • Agree x 1

20. No, I just use non synthetic 10W-40 oil.

    • Like x 1

21. Here are my final results: After two containers of this stuff, properly installed and run in (the second time after an oil change), it doesn't work as advertised. It did slow down the leak from my rear main a bit, but it's still leaking. The claim on the container that says "It really works" is inaccurate. It didn't for me. The two containers cost over $30.00, so when I determined that it didn't work, I sought a refund as their advertising says that it's "guaranteed". The NAPA store where I bought it refused to give me a refund, so I contacted the manufacturer. They asked a lot of questions and made it difficult to obtain a refund, saying that I had to go back to NAPA. This is after NAPA already refused to refund me. So I went back to NAPA a second time and a very unfriendly manager refunded me for the price of one container, acting very put out for having to do so. My recommendation: Do not buy Blue Devil Rear Main Seal repair. I was very disappointed by their product and the way they treat their customers.

22. I appreciate the testimonial on your experience. It sounds like you went above the normal procedure and it's such a shame that the company, Blue Devil, didn't stand behind the product.
    Napa may have lost a customer too. Thanks for sharing.

    • Agree x 2
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    billccm Well-Known Member

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    toolmanmike Moderator Staff Member FABO Gold Member

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Source: https://www.forabodiesonly.com/mopar/threads/has-anyone-tried-blue-devil-rear-main-seal-stop-leak.482037/

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