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How Do I Tell The Difference Between Rear Main Seal Leak Or Oil Filter


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i have a 1996 gmc halfton extended cab 4x4 with the vortec 350 the engine is leaking oil from the cover or plate that is between theoil pan and the transmission pan

(is this the flywheel cover or transmission plate?

i think its the either rear main seal or oil filter adapter.what im wondering is how do i tell the difference between a rear main seal leak and an oil filteradapter leakthe oil filter adapter i can fix my self but i cant fix the rear main seal. there is a plate or cover behind the oil pan at the bottom back of the engine. this is where the oil leak is coming from. please tell me what is leaking. thanks in advance for any help

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you have to wash it off with brake cleaner and go for a drive and take a look ,the oil filter adaptor seals/gaskets can go for a crap and have replaced many but still,go slow and inspect carfully

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Replacing the oil filter adapter gasket is easy and inexpensive. I just replaced the oil cooler lines, connectors, and adapter gasket/o-ring ('95 Suburban 5.7 K1500 130k miles). The whole job cost less than $60 and took me about an hour. After that I cleaned everything real well and found my oil leak had diminished by about 95%. I'll chalk the last 5% up to the rear main seal, and I don't think a few drops every few days is bad enough to worry about.

 

If you've never replaced the oil filter adapter gasket (or if you have and it's been awhile) I'd start there. If you disconnect the lines (and you probably will) make sure you replace the connectors.

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Replacing the oil filter adapter gasket is easy and inexpensive. I just replaced the oil cooler lines, connectors, and adapter gasket/o-ring ('95 Suburban 5.7 K1500 130k miles). The whole job cost less than $60 and took me about an hour. After that I cleaned everything real well and found my oil leak had diminished by about 95%. I'll chalk the last 5% up to the rear main seal, and I don't think a few drops every few days is bad enough to worry about.

 

If you've never replaced the oil filter adapter gasket (or if you have and it's been awhile) I'd start there. If you disconnect the lines (and you probably will) make sure you replace the connectors.

 

connectors/fittings ,yes,forgot,what he said ^^^^ lol

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thanks for the replies i washed off the bottom of the engine and watched the oil leak for a while.

the only place i can see it leaking from is the plate or cover that is betweeen the oil pan and the transmission pan this cover is about half the size of the oil pan and has 2 metal bars connected to it. is this the flywheel cover? but this is where its leaking from.

a couple people told me its probably the rear main and some others told me its probably the oil filter adapter. someone at a gm dealer told me the oil filter adapter can leak and if it leaks it can leak back in to the flywheel cover and apear to be a rear main seal.

 

is there any way to tell if the oil filter adapter is leaking without replacing it?

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  • 6 months later...
thanks for the replies i washed off the bottom of the engine and watched the oil leak for a while.

the only place i can see it leaking from is the plate or cover that is betweeen the oil pan and the transmission pan this cover is about half the size of the oil pan and has 2 metal bars connected to it. is this the flywheel cover? but this is where its leaking from.

a couple people told me its probably the rear main and some others told me its probably the oil filter adapter. someone at a gm dealer told me the oil filter adapter can leak and if it leaks it can leak back in to the flywheel cover and apear to be a rear main seal.

 

is there any way to tell if the oil filter adapter is leaking without replacing it?

 

Hey, not sure if you have fixed this or not. This week, on the drive to work, I lost my oil pressure. It was leaking from the filter adapter gasket. This o-ring had become so brittle it actually broke and it was dumping oil from it. I 'assumed' rear main due to the amount of oil, but my mechanic confirmed the oil filter adapter gasket. I too had that replaced along with new oil cooler lines which go to the radiator. Had I known this was the issue, I'm sure I could have done it myself. Since i assumed rear main, i didn't have the knowledge to fix that as it is one-piece and requires tranny removal, pulling oil pan, rear main on the crank, etc. Sounds like the easiest fix is that adapter gasket! Good luck!

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