# 67 GTO oil leak..



## Lvincentsr (Oct 21, 2021)

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* Lvincentsr*
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4 Posts 
#18 · 4 h ago

Hi Guys I’m a new member and I apologize if I’m adding my concerns about my 1967 GTO..It’s a newly rebuilt 400 engine with a TH400 transmission. I have been working on my car some 30 plus years..yes I said 30 plus years.. I installed the engine and transmission and started the engine for the first time checking leaks..having a 98% no leaks I was happy until I noticed a oil leak under the car.. I have a leak that looks like it coming from the rear main seal..The Worst scenario! It only leak when the is running..I check the bottom pan bolts and found them to be bet loose..tighten them now waiting for results..Any other ideas on rear engine leaks..


















 Reactions:armyadarkness


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## Lvincentsr (Oct 21, 2021)

Rear Main seal replacement,Is there a solid Circle seal to replace the rode seal on a 67 GTO?


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## armyadarkness (Dec 7, 2020)

Nice work! Glad you figured out how to repost.

I assume that youve already called the engine builder? 

If he's not responsive or able to help, then you'll have to torque the pan bolts yourself.

There are many solutions, but unfortunately, nearly all of them require pulling the engine back out.

There's a very valid reason that 100 people on this forum have leaking rear main seals. Any upgraded replacement for the rope seal, requires the engine to be removed


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## Lemans guy (Oct 14, 2014)

Army is right, if the seal is bad. But you might want. To relieve the crankcase pressure first with an ME Wagner dual flow PCV valve. You can install it yourself, about $130 dollars and it may fix the leak if the leak is the result of excessive crankcase pressure as many are.

Newly rebuilt engine have tight clearances and great pressure, but that causes high crankcase pressure too.

read the threads on here about PCV valves and go to ME Wagner’s site. You have nothing to lose as the valve will be great for your engine even if the seal is bad.

good luck!


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## Baaad65 (Aug 29, 2019)

Lemans guy said:


> Army is right, if the seal is bad. But you might want. To relieve the crankcase pressure first with an ME Wagner dual flow PCV valve. You can install it yourself, about $130 dollars and it may fix the leak if the leak is the result of excessive crankcase pressure as many are.
> 
> Newly rebuilt engine have tight clearances and great pressure, but that causes high crankcase pressure too.
> 
> ...


And plenty of breather flow as I found out


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## Baaad65 (Aug 29, 2019)

...as I got them and then after my first modification now they are drilled out even more then my first picture, still would pop the dipstick a little bit on wot runs so I had to crimp the dipstick onto the tube a little and hope for the best and yes get the Wagner pcv


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## PDub (Sep 8, 2019)

How do you determine if your rear main seal is bad? I also have noticed a few drops of oil below the car but only after running it. When sitting I don't see oil on the ground. I was going to get under the car to determine where it was coming from but didn't know if there were any tests or specific locations under the car when I can look to determine if the main seal is bad. Any advice would be greatly appreciated!!


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## Sick467 (Oct 29, 2019)

For finding oil leaks...clean the engine and surrounding areas well. I use degreaser or mild solvents like mineral spirits followed by an alcohol wipe down to get it to dry nicely. Then spray the suspect areas with spray can foot powder (you read that right). The key is very clean to begin with and a nice whitish coating of the foot powder. Run the engine a bit and look for the evidence in the powder. The remaining powder can be cleaned off afterwards.

Remember...a leaking rear main could be more of a problem with the PCV system and not so much a bad seal. Leaks on the floor from the rear main area could be from the rear main seal, transmission front seal (if auto), or oil from the heads to block mating surfaces, valley cover, oil pressure gage port/s, or from the oil pan itself. You should remove the flywheel cover to help locate where it's coming from since the cover can catch many of the potential leaks in that area and it will drip from the bottom of it without being able to see the source.


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## Lemans guy (Oct 14, 2014)

When hot the oil is thinner and under pressure in the crankcase…

.when cold it is thick and under no pressure…..

Great tips from sick to help find the leak, the flywheel cover can be taken off, 4 bolts, and clean it inside and out. Sounds like your leak is small.


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## Baaad65 (Aug 29, 2019)

PDub said:


> How do you determine if your rear main seal is bad? I also have noticed a few drops of oil below the car but only after running it. When sitting I don't see oil on the ground. I was going to get under the car to determine where it was coming from but didn't know if there were any tests or specific locations under the car when I can look to determine if the main seal is bad. Any advice would be greatly appreciated!!


My oil came from the dipstick popping up, sprayed on the firewall and dripped down so I had to trace it back because it was hard to see on the black paint then took a while to drip down, also see if oil came out of the breather and blew back.


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## PDub (Sep 8, 2019)

Baaad65 said:


> My oil came from the dipstick popping up, sprayed on the firewall and dripped down so I had to trace it back because it was hard to see on the black paint then took a while to drip down, also see if oil came out of the breather and blew back.


Yes, I noticed oil splatter inside the engine compartment on the passenger side fire wall. My breather cap on the valve cover is located on the driver side only so I don't think it came from there. It must have come from the oil dipstick or blow back from my other valve cover (passenger side). Anyway, I think I'm going to try the M/E Wagner PCV vavle to see if it will offload pressure during high revs.That will be cheaper than pulling the engine to replace the seal.


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## Baaad65 (Aug 29, 2019)

If the motor has alot of horsepower you probably could use two breathers and make sure they're drilled out, the way mine were when I got them was a joke with pin holes for air flow. I also tried the Mr. Gasket breathers with the element and in one pass the elements were getting oil soaked so I cleaned them up and returned them. I also cut the foam ring in half to make a narrower donut then glued it to the top inside of the breathers because the foam would get sucked down covering the holes. When the Wagner is tuned right you can feel the suction on the valve cover opening at idle but then at wot the motor makes pressure and it has to get out. I also picked up a rubber vacuum elbow to hook the vacuum gauge to for tuning because it's hard for the gauge hose to bend while you're holding the valve into the valley pan down into the intake, I pushed it down with the allen wrench so I could adjust as I held pressure down. The directions explain how you have to do this.


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