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Rear main seal leak or oil pan leak?

Rear main seal leak or oil pan leak?

Postby Daniel2 [OP] » Oct 08 2019, 1:55am

Hello I have a 2011 Silverado 1500 with 5.3. I have noticed that I have some oil on the bottom of the transmission on the inspection hole cover. I took the cover off and there is oil running down the oil pan but there is no oil on the fly wheel. Is this a rear main seal or the oil pan gasket? Thanks for the help.
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Re: Rear main seal leak or oil pan leak?

Postby 19trax95 » Oct 08 2019, 2:18am

It is pretty much a guessing game for someone to give an answer as to what's leaking.

I would clean it really good, put some dye in the oil and run it then check to see where its leaking.

You can buy the UV dye kits at the parts stores.

Or just clean it and see if you can spot the source without the dye.
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Re: Rear main seal leak or oil pan leak?

Postby Daniel2 [OP] » Oct 08 2019, 2:25am

19trax95 wrote:It is pretty much a guessing game for someone to give an answer as to what's leaking.

I would clean it really good, put some dye in the oil and run it then check to see where its leaking.

You can buy the UV dye kits at the parts stores.

Or just clean it and see if you can spot the source without the dye.

I thought it was my oil cooler lines where they bolt up right above the oil filter. I believe they were leaking because my oil filter had oil drips on the bottom of it. The cooler lines wouldn’t cause oil to be running down the oil pan in the bell housing though would it?
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Re: Rear main seal leak or oil pan leak?

Postby 19trax95 » Oct 08 2019, 2:38am

Anything is possible. Oil will make it to some crazy spots. Especially with leaks underneath since the air flow will track the oil all over.

I've had oil leaks come from the front crank seal and end up all the way back at the trans. Made it look like the pan gasket was leaking, but it was streaming down behind the vibration damper and the the air would catch it and take it all the way back.

So the only way to know for sure is to clean the old oil, and then run it and watch for where its coming from
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Re: Rear main seal leak or oil pan leak?

Postby FoxProDenali » Oct 21 2019, 8:33pm

I thought my leak was isolated to the oil cooler lines but I just replaced them and it seems even worse. I have drops hanging from the bottom of the transmission bolts, oil pain, some on the filter, some on the trans cooler lines and the stabilizer bar is usually pretty slick. Really annoying.

I haven't tried the dye yet, but I guess jacking it way up and cleaning everything really well will go along way. Do you guys just use break/parts cleaner and a brush or what?
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Re: Rear main seal leak or oil pan leak?

Postby Daniel2 [OP] » Oct 21 2019, 8:57pm

FoxProDenali wrote:I thought my leak was isolated to the oil cooler lines but I just replaced them and it seems even worse. I have drops hanging from the bottom of the transmission bolts, oil pain, some on the filter, some on the trans cooler lines and the stabilizer bar is usually pretty slick. Really annoying.

I haven't tried the dye yet, but I guess jacking it way up and cleaning everything really well will go along way. Do you guys just use break/parts cleaner and a brush or what?


I’m replacing my oil pan gasket tomorrow mines 4x4 so I will have to drop the diff. Luckily I have access to a lift. Yes I would just use brake cleaner and a rag.
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Re: Rear main seal leak or oil pan leak?

Postby FoxProDenali » Oct 21 2019, 9:17pm

Nice, keep us posted. I had to lower the diff for the oil lines. It's not bad, only 4 bolts.
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Re: Rear main seal leak or oil pan leak?

Postby FlameOut » Oct 21 2019, 9:18pm

When I thought I had a rear main seal leak in my 5.3 2004 Silverado, it ended up being the oil pressure sender unit that is located at the top rear of the engine. I replaced that and all was good. I assume they are in the same place on the 2011 models?
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Re: Rear main seal leak or oil pan leak?

Postby Daniel2 [OP] » Oct 21 2019, 9:50pm

FlameOut wrote:When I thought I had a rear main seal leak in my 5.3 2004 Silverado, it ended up being the oil pressure sender unit that is located at the top rear of the engine. I replaced that and all was good. I assume they are in the same place on the 2011 models?

Yes they are but my leak is in the bell housing
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