Ladies and gentleman, I have an oil leak that has every gear head, professional mechanic, and performance hot rod shops scratching their heads. I have a '75 455 in a 67 skylark. I currently have the TA stock oil pan on it with the additional quart of capacity. I have replaced the rear main seal with neoprene a month ago to stop an oil leak that was happening in the rear of the engine, and dripping down the back of the oil pan at a very healthy rate. That was one engine pull. It still leaked the same amount after that install. I pulled the engine again and bought my current pan thinking it was my aluminum pan shifting on me when the engine heated up as it only leaked when the engine was hot. I replaced the aluminum with my steel TA pan. This looked good at first, dry as a bone when it was sitting and idling, but when i road tested it it was throwing oil as just before, so I pulled the engine again. This time I put it on a stand and installed the pan under ideal conditions, using all new gaskets and perfectly placed gasket goop, it was picture perfect!! Once again, bone dry when idling and getting on it in park. As soon as i brought it on the road and hopped on it, the next day mind you, she started throwing again out of the same areas in the rear of the engine. My theory after all this frustration is a crankcase pressure issue. The PCV valve is working properly and i have breathers on the valve covers. I think i am still building pressure somehow on the bottom end. I was wondering if anyone has experienced this kind of problem with oil leaking on any pan in any buick motor. My next step is to pull the engine for the 4th time in 4 weeks and weld an NPT fitting to the pan and put a gauge on it to see if I am building pressure in the bottom end crankcase. If I am, i will put some sort of breather coming out of the oil pan. I am about at my wits end.......so much time and money has been invested in this, and i cant even drive my car....absolutely the most frustrating thing I have ever worked on. Thanks for enduring this long story, any help would be fantastic!!!!
zero blow by and i know for sure it coming from the oil pan, i can see it weeping while the engine is running after i drive it
I can feel you pain. There is nothing worse than trying to fix a bunch of oil leaks. I'm going to run some stuff by you from 40 years of fixing leaks and let you see what you think might apply to you. First, it is not uncommon for it to not leak setting idling and leak when driven. You may be on the right track, thinking crankcase pressure. I'm not sure how old your engine is and how many miles it has on it, but both will have an impact on crankcase pressure pushing out oil. I used to hate to try to fix the leaks on an old Chevy 235 6 cylinder truck that was half wornout and had all kinds of crankcase pressure and the fact that they only had a road draft system. You could replace every gasket and seal and get them back running and they looked fine, but a week later they would come back in the shop with oil dripping off everything. Now, a second point, oil runs down hill, always look high for a leak. What you might think is a pan gasket can be the rear of the intake( something that will hardly leak at idle) or even the rear of a valve cover. Other leaks in the rear can be the cam plug or oil plugs in the block. Also oil can leak between the main cap and block in the rear main seal area if it is not sealed correctly. Also, large amounts of RTV are not always your friend. Most important before using any sealer or RTV, is EVERYTHING MUST be oil FREE and DRY before using any sealer. There are additives that you can put in your oil and use a black light to locate the orgin of leaks, it might be smarter to pay someone to check it with blacklight than to keep taking the engine in and out. Hope some of this helps. Jim N.
you stated "My theory after all this frustration is a crankcase pressure issue." Crankcase pressure is blow by.
Black light the best test in the world, could be anything....even heaven forbid....a crack in the block. Put the dye in and trace it with the black light.....mystery will be over. plus you can put on the tie dye shirt, and head band, burn some %oo#!es, in the pitch dark garage....
My engine is not that old, maybe 1000 miles on the motor. to your second point, i can atcually see where the oil is weeping from when i am looking under the engine while it is running, everything else is bone dry above and below. This engine is on point with everything other then then this leak. It is the only wet area of the entire engine. Any other thoughts after this info?
there is no other blow by on the engine other than where i stated, everything is bone dry other then the rear of the pan.
I have a K&N valve cover breather with the shorter tube, every thing is fine until I get into it then it leaks like a siv, I"m going to install the longer tube to bring the filter further up from all that oil splashing under the valve cover. Luis
What are you guys using for sealer? Most of the stuff at the auto parts stores is just plain crap. Go to your local Nissan dealer and get their High temp sealer. Oddly enough it says Made In USA on it. p You will never ever have another leak using it. :beer
Sounds crazy, but maybe your block is porous, or there's a minute crack in the area where you see the leak?
Rear seal is installed in the right direction. I am indeed using the best gasket goop money can buy, my pop is a machinist so it comes free of charge, and it is made in the USA, high temp red RTV. The leak is coming from the rear of the pan, when looking up at the pan, the last bolt on the right and a tiny weeping from the center of the rubber pan seal. My questions is would you necessarily see a minute crack, cause i have been staring at the bottom of that block for the last month and nothing caught my eye, but then again i was not looking for it. A crack in the block would make me go over the edge.:blast:
Remove and inspect the neoprene seal. If the fit isn't correct, they burn up immediately. Once burned, they wouldn't leak too bad at idle, but go out and mash the gas and oil would be coming out of the torque converter inspection cover drain hole when I got back. All it took was for the oil to be forced up against the back of the crankcase during acceleration. I kept burning up those Ford seals that are supposedly a drop in, no matter how well I polished the crank, and no matter what I did to prelube the seal. The Ford seal just hasn't fit well at all in the last two big blocks I assembled. So I went back to the file fit Cadillac 472-500 seal like I always used to use, and have no leaking whatsoever, not even a film of oil. This is on three engines that I have in use currently. And I'm doing a short block with one right now. Won't even waste time trying the Ford seal anymore. For me, the Ford seal was riding the crank with way too much pressure and they came out with the seal lip burnt to a crisp. The Cadillac seal comes a tiny bit big, which allows you to fit it to your block's exact dimensions. That groove was made for a rope seal, so I don't believe that accuracy was a big concern. I leave .010" protrude on all four corners. This loads it hard into the block so that it will not spin, yet leaves just the right amount of pressure on the crank. There is no drop in rear main seal for the Buick 400-455 in my opinion.
I had a simular issue it was the rear main seal I thought it was the pan gasket I had to put a small amount of sealer on the ends of the cap it was leaking between the main cap and the block and make sure the seal is not flat with the block it needs to be up 1/4" and down on the other side....from t/a web site sure you have read this before but... Always replace both upper and lower halves of a split seal as a unit. Also, clean any old sealant or foreign material from the cylinder block, bearing cap and crankshaft sealing area. Using a 3/8”, long reach center punch, make a series of punch marks inside the rear main seal receiver groove of the rear main cap and the block (if crank is removed). Prevent from making a punch mark where the two seal ends will meet . Also, slightly chamfer the receiver groove edges at the parting line on both the cap and block. Lubricate the seal halves with engine oil both to aid in installation and to prevent a dry lip upon start up. However, wipe the mating surface of the two seal halves dry before assembling the bearing cap to the block. Install the seal with the large sealing lip pointing toward the engine. Stagger the mating ends of the two seal halves so that one is approximately 1/4“ above the parting line and one is 1/4” below the parting line. Apply a thin coat of RTV material to the bearing cap chamfer and to the cap mating surface adjacent to the seal but NOT ON THE SEAL END. Use extreme care when installing the main cap to ensure proper seal mating within the receiver groove of the cap
I can't believe yoose guys are pulling engines before you actually find the leak. I'll second the dye and a black light. If you've never diagnosed an oil leak with one, then you don't know what you're missing. The best sealer I've used is by far Loctite's 5900, aka "The Right Stuff", available at NAPA. Get the 6 oz cartridge, not the cheeze-whiz can.
