[Nu2pontiac]

I thought I had a rear main seal leak until I read a post that said that a telltale sign of a rear main leak is oil on the flywheel. I did see a drop of oil waiting to drip at the back end of the pan where the rear main is but . . . .
Here’s the story:
My 389 has leaked most at start-up.
1. Last summer the few times I started my car oil would flow out at start up (I’d guess about 2+ oz) and then slow down quickly to but a drip now and then. Higher or lower RPM’s have no impact on the leak.
2. When I started the car after several months of non-use it leaked at start-up but not near as much as in the summer (I’d guess about 1 oz).
3. When starting the car today (about 10 days after my last start) the leak at start-up was minimal, (maybe .25 oz) and after a 10 mile drive a very infrequent drip.

Do you think the leak I have at start up sounds like a main rear main seal leak or could it be something else? I’m wondering if I would just drive the car more – I don’t drive it much at all – if that would cure it. Rick

[torqjunki]

Once you get a leak like that, it will continue. Is this a rope seal or 2 piece lip seal? I have had some luck with the CD-2 stop leak stuff with a rope seal even though it is not really designed for such. Works better with lip seals. Also helped to hook up a evac hose from a breather on one valve cover to the underside of air cleaner bottom to pull pressure from the block. Most will tell you to run a PCV valve as well. It will pull a slight amount of vacuum from engine at idle only. On a recent post from someone here, they had great results confirming a leak using the dye that goes in the oil and a black light I assume. FWIW...My rear seal leaks just a little and does not stay on flywheel. It will end up on back of pan, starter bolts and oil filter areas.

[Nu2pontiac]

Any ideas on the different amounts of oil that leak at start up? I am assuming there is a rope gasket. Engine was rebuilt before I bought the car. Would this be an indication that it is the real main seal?

[gtofreek]

It could be the rear oil pan gasket that is leaking. Pontiac uses at least three different rear pan gaskets where it goes over the rear main cap. They changed over the years. If who ever built the engine used the wrong seal, that might explain your leak. Then once the oil level gets lower, the leak slows down. Just a guess, never seen one leak that bad before and slow down. The 389 should use the cork rear oil pan seal. The later seals were rubber.

[Nu2pontiac]

I agree gtofreek that I could have some leaking from the pan in the rear, but regarding the oil level I think there is too little variation.

[gtofreek]

When running, the oil level will drop quite a bit. You will probably have 1-2 quarts pumping through the engine at any one time. But, like I said, I have never heard a problem quite like this before. Let us know what you find.

[geeteeohguy]

I would: remove the clutch /flywheel inspection cover, clean the entire area with brake cleaner or equivalent, blow it dry, put it up in the air, and have a helper start it up while you are under it with safety glasses and a good flashlight/drop light. You need to clean it up and see it in action. That much oil, you WILL see. No sense speculating with a dirty engine....you'll be chasing ghosts. I agree, never heard of an oil leak behaving this way. Weird.

[pfilean]

I thought I had a main seal leak until I pulled the engine and the back of the flywheel was dry. Rather that make a leak where there was none I did not take off the rear main cap but put on a new pan gasket (the old one was really suspect when I took it off). No leak this last year.

But you describe a different problem when you get it to leak at start up and not after the engine is warm. Pontiac has a plug in the end of the oil gallery on the drivers side(like most engines). It is under pressure, which of course is higher just as you start cold, and pressure will lessen as the engine warms. Perhaps the plug is not properly installed or tends to expand with temperature when hot and seal off the leak path. Try and check that out. You might get an idea from the preceding posts.

The corresponding plug on the passenger side is not under pressure and it will not likely cause a leak. On that side the plug under pressure is a screwed in plug ahead of the distributor/oil drive and many builders like to add a small hole in to better assure lube to the drive gear on the rear of the cam.

[Nu2pontiac]

[IMG][/IMG]
It’s great to be able to use these forums and the knowledge base here. First, it’s not that the engine doesn’t leak at all after start up. It leaks more than I knew. For leak on my driveway I discovered this morning see photo. The car had not been running very long an marked that spot in +/- 5 min. but the next 50 ft. of driveway may have had one drop. I found a few quarter+ sized drops where I turned out of my driveway and then again at the stop sign about 50 yards up the street where I turned and accelerated.

Last night my car was in a buddy’s garage and this morning I saw it leaked some overnight (see picture which has a quarter next to the spot on the floor so you get an idea of the size).


Looking from underneath the engine I saw two drops hanging directly over the spot on the garage floor (see picture).


There was also a fair amount of oil at the bottom of the flexplate cover (picture also has a quarter in it).


Looks like either the real main seal or the oil pan gasket at the rear or both are leaking.

Why the greater volume of oil leaking at start up? Here’s my best guess. Tell me what you think. The flexplate cover catches some of the oil and it builds up in the bottom of it. The cover is designed with about a ¼” round hole that is drilled off center (not sure why), which allows oil to build up in there. The longer the car sits in the garage the more the flex cover fills. At start up the vibration and flexplate serve to clear out the oil in the bottom of the cover. I have seldom used the car because of the amount of oil coming out at start up, which gives the drip time to fill up to the hole in the flexplate cover. If it overflows while sitting there I don’t notice because I have an oil pan under the car that is, well, oily!

The bad news is the engine must come out. The good news is that there may be multiple leaks to fix all at the same time! So far, however, only the bad news has sunk in. I’m thinking about doing this with some buddies, but does anybody know a Pontiac guy in the Philadelphia-Lancaster-Harrisburg-Delaware- Maryland or NJ area who does this kind of work? Rick

[lust4speed]

Leave the dust cover off and you will get a much better idea of what's going on. None of my cars run the dust cover, and if nothing else not having a cover keeps the converter a little cooler.

Try and rule out valve cover and valley pan leaks before committing to pulling the engine. The lack of room to really look at the back of the engine and the flexplate tossing oil everywhere can mask where the true oil leak really is coming from.

[Nu2pontiac]

Pulled the engine and when looking at the rear seal it was dry! Oil was leaking out of the rear of the pan gasket. Put in a new graphite seal and will be putting in the BOP one piece pan gasket.