I have a recently rebuilt 440 (now a 505) that I have been driving around locally with absolutely no leaks...not even a drop. I've had it on the interstate, but only for a few miles at a time to see how it went, with no issues.

Well, yesterday I took my car onto the interstate (60 to 80 mph depending on traffic) for the first real distance (only about 20 miles) and I'd say at about 10 miles my rear main seal 'totally' blew out. I say that because my interior suddenly started filling with smoke (had the windows up.) Knew it wasn't a fire because it had that burning oil smell.

The leak is so bad that when you stop and look under the car, oil is pouring out almost in a stream, not just dripping out. Sort of in that in between area where you have drops coming out in such quick succession that it is just about a continuous stream, but not quite. And the back of the car was just covered in (clean) oil.

Anyway, I know I have to fix it now, but of all the internet searches, I haven't seen anyone describe such thing. It seems it is usually just some drops that develop over time.

So I am wondering if this is something that 'just happens some times' or if there is some particular cause of this particular scenario that should be rectified before I replace the seal.
I don't want to replace the seal and have this happen all over again because I didn't address some other underlying issue that might have cause it.

Thanks for all the help. YOu guys are an excellent resource to guys like me who barely know what we are doing!!!

I just wanted to add that I have a PCV valve and crankcase ventilation. And I don't believe that I have much blow by, given the motor is just rebuilt and there doesn't seem to be any smoke coming out of the exhaust or valve cover vent.

Make sure where the oil is leaking from FIRST If it is leaking from the rear main seal onto the back of the crankshaft flange it will sling the oil out onto the converter flex plate and converter. If it is not doing that it is NOT the main seal
I've seen more than one rear main seal replaced when it wasn't leaking
IHTHs, let us know what you find
The rear main seal can not and will not pour oil out unless one of the side seals is really messed up
I have had the rear cam plug leak, one of my friends had a rear oil galley plug leak and I have seen many valve cover gaskets leak after being ran several times without being retightened

Yes, I have thought about the possibility that a plug let loose.
I just figured that if that happened, it would be MUCH worse than it is (as bad as it is.)

But there is no external leak anywhere. Definitely not the valve covers or oil pressure sending units. The oil is pouring out from between bellhousing and bellhousing cover. So the leak is definitely coming from the back of the engine, inside the area covered by the bellhousing.

I haven't crawled underneath and pulled the cover off. I just put the car right back in the garage because I am just so disappointed with the thing right now.

Sounds like cam plug or oil galley pipe plug backed out. Drop the transmission. Cam plug or galley plug is an easy fix. Easier than the rms.

I had a 446 i built on the dyno several years ago..... The rear seal leaked so bad I thought I must have put 1/2 the seal in backwards.
It just ran right out....... But it started doing it right off the bat.

The seal was installed correctly, and ultimately it ended up being a distorted original seal cap that was the problem.
The oil was actually leaking around the seal in the cap, not "past" the sealing lip.

As Cab said, make sure you know where it's coming from before tearing anything apart.

Do you know if your crank has the grooves in the seal surface or not?

I have seen it where the grooves are pretty aggressive and just wear the lip right off the seal.

I also had a customer built stroker on the dyno once that started leaking really bad shortly after we got the motor running.
On that one, it ended up being I little chunk of the lip had gotten torn off the seal and that just created a little hole for the oil to poor out.

I don't really recall if it had the grooving in the crankshaft to push the oil back or not...or what the grooving looked like if it did.

Tomorrow I am going to get under there and do as much investigation with a flashlight as I can, to try and determine if is the crankshaft seal or some other seal/plug.

Did you look at the top back of the block? oil sending unit or gauge pressure line leaking?

Yes. Definitely not coming from sending units or valve covers. Dry as a bone at the top of the engine.

You might also pull the flywheel cover and fire up the engine. Then have a look about the area in question looking for where the oil may be gushing out. It is even possible that could be the pan gasket where the 2 pan bolts screw into the rear main retainer. Almost impossible to differentiate with flywheel cover in place.

As mentioned earlier, be very careful in ruling out valve cover gasket at rear of engine. They can fool you.

Given all that, I too once had a rather catastrophic rear main leak oil up the entire rear bumper of my car. Made a nice mess baked onto the ceramic coating on my TTI headers. Took as long to clean them as to replace the seal.

I don't really recall if it had the grooving in the crankshaft to push the oil back or not...or what the grooving looked like if it did.

They dont put rope seal grooves in newer stroker cranks do they?

I took my car onto the interstate (60 to 80 mph depending on traffic) for the first real distance.... Could of been a issue from day one, just now you your seeing it because it had full heat and thinned oil and good constant pressure.

Like the others say, pull that cover, id say anyway ya look at it, its a semi easy fix in the big picture.

Yes, some brands of cranks do....... And the grooves in the aftermarket cranks are not like the original cranks at all. The grooves are fewer, deeper, and at a shallower angle.

Great news. Although I still need a little help to make sure I am remembering correctly:

Got underneath the car and low and behold...one of the rearmost oil pan bolts was missing!
If I recall correctly, when I put the pan on, that bolt hole leads to the INTERIOR of the block, correct? It passes straight thru the main seal cap.
If so, that's like a great big hole at the rear of the pan! I'm surprised more oil didn't come pouring out. (meanwhile, I will be googling images of that cap on the block)

I also pulled off the cover and the flywheel, converter are as dry as a bone. BUT there was a TON of oil sitting in the bottom of the bellhousing. And the INSIDE of the cover seemed a lot more soaked in oil than the outside, which is strange if the leak is coming from the outside (oil pan.)

Just google some photos and yep, those holes go to the interior. SO I had a gaping hole at the rear of my sump.

I feel kinda stupid right now, but I'll take that over having to replace the main seal any day!

Thanks everybody for your help.

If there is a hole all the way threw the cap that indicates that at one point someone put too long of a bolt in it a broke threw. if your going to use that retainer you have to put sealer on bolt .Hope this helps.

Yes, it goes all the way thru. I stuck a screwdriver in there (carefully) a couple of inches with no resistance. All the bolts I put in there were the original bolts with the washers that don't come off and are quite short. So it wasn't me! lol.

And I reinstalled a new bolt with sealer this time (and took out the other one and put sealer on it, too.)

Drove it to one end of town and back and no leaks.

Inside of cover being wet is either because there is no tight seal(no gasket there) between cover and block,,,,or because front of flywheel cover was pinched slightly over rear of pan leaving a gap between cover and the block allowing oil into cover from your leak source. This is why a leak at rear of pan gasket at rear main retainer can fool one into blaming a rear main seal leak as noted in my earlier post.

Well, you were right. That's the area the leak was coming from, but it sure looked like it was coming out from between the bellhousing and the cover.

Nice to hear of an easy fix on a potential headache.

Great post.
Glad it was simple fix