I had a great experience over the last several months chasing down
oil leaks on my engine. As you all know, almost every
oil leak on an FE-type block, or most blocks for that matter, eventually get to the rear and bottom of the bellhousing and mimick a rear main seal leak....or
oil pan leak. My engine started leaking oil at about 5,000 mi. Before that, the only leaks had come from the valve covers, and I replaced them with the cork gaskets and no more leaks. However, the leaks started flowing and flowing big, like a pool 8 inches in diameter or so after a couple of hours of sitting when hot.
Not at first seeing any noticeable leaks from above, did some sub-frame checking with the flashlight and saw good doses of oil streaming down from the rear of the pan down the bellhousing cover, and even from the rear of the bellhousing where it mated to the transmission. On trips of more than a few miles, the oil would stream down mostly on the pass side frame rail, spray all over the rear trans mount, onto the rear crossmember, all over the 3rd member and onto the gas tank. A real mess.
So first order is to check torque on the pan bolts. OK, although the rubber gaskets look like they're pushing out a bit, so that may be a project for another day. Go for a run, no change. After clean up, thinking it may be coming from the rear of the intake manifold, since I do see a little fresh looking oil at the right rear, I decide after fretting for a couple of weeks, to pull the intake and re-seal. Pulled, checked fit, and everything seemed OK, but put in new steel sandwich intake gaskets and pure Right Stuff front and rear walls and at corners. Reinstalled everything, adjusted lifters, added fluids and went for a run. No change, still leaking. Newman!!
Told my friend Jim about it, he has a leak detector kit!!! So we get the kit, and put the dye in the oil. Sure nuff, more new oil coming down the back of the block from where it meets the oil pan. Nowhere else that I could detect with the blacklight. So now I'm really fretting, because I don't want to pull the engine to get to the rear main seal, which is the only other place I could think of. So I fret some more, and leave it alone for a few more weeks, cleaning the chassis and assorted parts after every trip, hoping it was going to go away. A total mess.
Then a few weeks ago, I had the car at the end of the driveway with the front wheels in the gutter, so the engine was angled just so the sun was directly beaming down to a very small area at the rear of the block just below on the right side where the intake manifold meets the head, AND THERE IT WAS. A little stream of dyed oil slowly seeping out of an oil galley plug with a hex slot in it.
Due to its proximity to the side of the block, you couldn't openly see any oil flow down the side of the block to the rear bottom where it meets the bellhousing, even with the blacklight! I pulled the steel plug, teflon taped it up and reinstalled. Success!!! Stopped leaking. Story over? Not so fast.
A couple of weeks of pleasure driving go by, then I start seeing oil running down the driver's side frame rail, looking like it's coming from around the mechanical fuel pump or oil filter block area. NUTS!! I clean thoroughly and go for a run, then get under it and it looks like it's coming from the oil filter block and lines area. Tighten the bolts, but they're already tight. Then I see IT!!! Another oil galley plug, just above the fuel pump. It looks like it has a little fresh oil on the block area around it, which could be dripping down onto the fuel pump and oil block area. It's the little white area in the picture below above the fuel pump.
Same kind of plug with pipe threads like the last one. So I pull my coil to get to it, and apply the teflon tape, and SUCCESS again. No more leaks.
And just for good measure, I pulled the other accessible plug just above the starter and sealed it as well.
Now there are at least two, maybe three more plugs at the rear of the block just ahead of the flywheel, but for the same reason I didn't want to change the rear main seal, those will have to wait, but they don't seem to be leaking now.
I think these plugs started leaking due to various heat/shrink cycles on dissimilar metals owing to more and more hours on the engine. And a gap finally formed. Just wanted to share, so what appears to be something really big, may only be something easily fixed at the end of the day. Nice!!