Help to diagnose Oil leak under truck.

[Winnipeg Lawns]

My truck is 92 GMC sierra with a 350.. 2 wheel drive.

I have an oil leak, the oil droplet will form right on the oil pan plug nut and drip to the pavement when parked.

I thought it might be the gasket on the nut so I bought one, nothing changed.

I've been told it's might be either a rear oil seal leak or a Oil pan gasket leak.


Here's the thing. I just filled it up with oil and when I park for 20 minutes like 2 cups of oil will leak out.. *when it's parked*.

Once the oil level gets so low that it's not on the dip stick, it will only drip a couple drops but it freaks me out there's no oil. But there is quit a lot left as I took of the plug, thinking it was empty, and lots came out.


So.. Now I'm thinking it's the Pan Gasket and it leaks like crazy till the oil level gets below the gasket level... would this be right? or Would a rear oil seal leak like crazy while parked?

[CLARK LAWN]

First thing, power wash it real good. Get all the old oil off then it will be easier to find. Second is that pan looks really rough, you my be putting a new pan on. Lucky those are a dime a dozen and easy to change.
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[123hotdog]

I know this sounds strange but I have the same truck and the valve cover gaskets were shot. Its a thought. I don't know if you can get a pressure washer under your truck to pressure wash it. I would replace the valve cover gaskets and the oil pan gasket ( they are cheap ) and thoroughly inspect that oil pan. I'll bet the metal is thin because of road salt. Make sure to clean off the old gasket really good. I don't have to tell you if it is the rear main seal, that the labor is pricey if you don't do it yourself ( I couldn't do it myself ) .

[nparish]

Use caution anytime you powerwash the underside of a vehicle.

[Pietro]

Just spray some degreaser on it and hose it down. Then get to the autostore and get some trackdye. Its the dye that you add to the crankcase. Then get a cheapo blacklight. Let it sit, and one night check with the blacklight, it will light up the trackdye showing you where the leak is.

[hosejockey2002]

Originally Posted by CLARK LAWN

Second is that pan looks really rough, you my be putting a new pan on.

x2. There could be a corrosion caused leak just about anywhere on that pan. If you pull it to replace the gasket, like others have said just replace the pan, they aren't that expensive IIRC.

[Winnipeg Lawns]

Let me re-ask the question. Can a diagnosis be made of where the oil is leaking from by the fact that it leaks like crazy when I fill it up with oil but stops when the level is just below the dipstick?

Does oil leak from the rear seal when a vehicle is parked like it would if there was a hole in the oil pan?

[CLARK LAWN]

like i said, clean it up real good then when it starts to leak you can find where it is coming from. i dont think it is the rear main. when the rear main goes there is oil all over everything rear of the engine. without cleaning it and seeing where it is coming from you are just guessing and may be just throwing parts at it but not fixing it.

[Winnipeg Lawns]

Well I was quoted $1000 to change the oil pan, LOL!

Apparently it's 6 hours labour. It's the last nail in the coffin for this truck. Lighting problem with trailer, rust on the wheel wells, broken power window on drivers side, lock doesn't work on the passenger side.