Oil Leak

[76sierraclassic]

I've got an oil leak that I'm wondering if you guys might be able to help me figure out.

I originally thought it might be the rear main since the oil was running down to the bottom of the transmission and dripping off, but I had it in the shop a couple of months ago and the mechanic said he couldn't get any oil to speak of to come out of the rear main. He cleaned everything up real good, but of course it's all coated in oil again. I looked from underneath this evening, and it almost looks like it's coming from the valve covers, but it's not. I don't have a lift or anything, so it was kind of hard to look around, but on the driver's side, the back of the block was "wet" all the way up to the valve cover, and on the passenger side, there was quite a bit of oil residue on the block above the starter.

Does anyone have any suggestions as to where the oil might be coming from?

BTW, this is a stock 350/4bbl with a stock th350 tranny in case you need to know.

Thanks,
Mike

[bigblock73]

Ask your mechanic to run a bottle of dye in the engine. I am not sure what it is called, but there is a dye you put in your oil, run the vehicle around for a day, then come back and shine a black light on the engine block. This will then tell you exactly where it is leaking from since the black light will expose it.

That is what I would do if you are positive you can't tell where it is leaking from.

[76sierraclassic]

Thanks for the suggestion. I may give that a try in the next couple of weeks if I can't find it otherwise.

Mike

[raceman6135]

The rear end seal on the intake manifold could be leaking.

Or the oil pressure sender, located just to the driver's side of the top of the block (behind the intake manifold) could be leaking.

DJS

[apstguy]

I had a problem with the rear sender next to the distributor and the valve cover. The valve covers can either be very easy to track the leak down to or very difficult. They can leak on the back or top and make it look as it is coming from elsewhere.

[76sierraclassic]

Thanks for the suggestions guys. I'll give those areas a look and see if that's where it's coming from.

Mike

[KShortell]

WOOT! Hold the phone...

Do you have the factory towing package with the external oil cooler adapter at the spin-on filter location on the block?

I just fixed an oil leak like you describe. I had the rear main, flexplate, valve stem seals, etc. just replaced for other reasons, but still had an oil leak. It turned out to be the $4.10 gasket between the aluminum adapter housing and the block.

Good luck!

[76sierraclassic]

Originally Posted by KShortell

Do you have the factory towing package with the external oil cooler adapter at the spin-on filter location on the block?

I don't think I have this option, but how do I know for sure?

Mike

[KShortell]

You'll have two oil lines coming out of an aluminum housing at the oil filter. These lines lead up to an oil cooler in front of the A/C condenser (if equipped) and radiator...

[Paso76GMCstepper]

I too had an oil leak that I had a hard time finding. In town it didnt leak bad at all. If I drove over a bumpy road I would have oild all over the rear of the pan and transmission. I changed valve cover gaskets still oil, I changed oil filters stil oil leak. Well after I decided to pull the engine to redo the engine compartment I found where it was coming from. Now dont laugh but it was the timing cover to oil pan gaket up FRONT on the engine. The metal on the timing cover and pan were so beat up that everytime I hit bumps it sloshed some oil out and then it went straight back. I too thought it was the main seal. I changed timing cover and oil pan. New hard parts and gaskets no leaks no drips no errors.

Just my .02 cents.

It really drove me nuts because I thought since the oil was on the tranny and the back of the motor that it had to coming from the back. In this case it was the front and the air and the fan pushed it back to where it hit about middle of the pan and then all the way back. Now I dont leave puddles of truck blood everywhere. And I have 60psi oil pressure as opposed to 45psi.

Tony

[Pushrod]

It's probally the gasket on the bolt on adapter where your oil filter screws on, had the same problem on a truck of mine, it stopped when I put the new kit on.