Engine oil leak

[Bigbertha78]

2004 Tahoe Z71, 150K miles. Ok, so I have discussed this leak before yet keep coming up empty! Changed valve cover gaskets and still leaks! Have these drops coming from the drivers side up high! At first, I thought the oil pan was the culprit! I have no fluid inside the transmission circle cover! Sprayed cleaner all along back side of intake, oil pressure sensor is not leaking and crankshaft sensor is not leaking either! Cannot find any leaks what so ever, tried letting truck run for 15 minutes and no leaks, drove truck 10 miles at varying speeds, no leak! Any suggestions would be greatly appreciated, thanks!!

 

[ivin74]

Its the rear main seal, its a common issue with this trucks. If you do replace it, do the oil pan gasket as well

 

[Bigbertha78]

I'm not convinced that it's the rear main seal. I have removed the transmission cover and the housing where the flywheel and converter are is dry as a bone. I did notice the head toward the firewall at the bottom wet, but it is coming from higher up.

 

[bottomline2000]

If it's not the block off plate..check your oil pressure sender.

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[rockola1971]

Timing cover blowing backward? Found any hints of oil toward front of engine? Are you 100% sure its oil and not brake fluid (master cylinder) or power steering fluid, have hydroboost?

 

[Bigbertha78]

I do have a bad oil leak on the front of the valley pan, but nothing going down the front. Maybe the oil from the front of the motor may be blowing back! I do have the hydroboost system but no leaks on that system, brake fluid or power steering. The oil pan is wet around the seam but nothing to the point of dripping yet. I am going to replace the top end seals all the way to the valley pan gasket first, then replace the oil pan next. I have some Delphi knock sensors a friend gave me, but I here the AcDelco are way better. Also, the oil pressure switch on the back, does it matter which brand installed?

 

[Tkrysl]

Probably a silly question, but would you notice an oil level low with a rear main leak? I had a bad oil leak once on an old 4.9 Ford and never had low oil on the dipstick but buddies told me it was a rear main.

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[Bigbertha78]

I changed the engine oil Dec 9th and almost have 600 miles on the truck since, yet I have not noticed a drop in oil level on the dipstick! No engine lights either! Cleaned behind the intake yesterday and there is no oil, when I go underneath the drops are back! Gonna have to look harder!

 

[rockola1971]

Probably a silly question, but would you notice an oil level low with a rear main leak? I had a bad oil leak once on an old 4.9 Ford and never had low oil on the dipstick but buddies told me it was a rear main.

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If the rear main were leaking there would be no way to escape having the tranny bellhousing, torque converter wet with oil. You wont notice a cup or two of oil leaking by looking at the dipstick.

 

[corvette744]

I never bother going thru all this if its not an obvious leak.Put some oil dye in it and blacklight it- save yourself a lot of time and headaches.You will know if you have 1 or more leaks and exactly were its coming from-no guessing.

 

[Tkrysl]

I never bother going thru all this if its not an obvious leak.Put some oil dye in it and blacklight it- save yourself a lot of time and headaches.You will know if you have 1 or more leaks and exactly were its coming from-no guessing.

Recommendation on a dye product, please?

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[corvette744]

Recommendation on a dye product, please?

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https://www.pepboys.com/product/details/563222/00987?quantity=1

 

[Cyclemoe]

Take a mirror and look at the valley cover at the rear on the drivers side. Mine is leaking a bit there on my 6.0 2500 burb, and I have a couple friends with the same issue

 

[treehan77]

Take a mirror and look at the valley cover at the rear on the drivers side. Mine is leaking a bit there on my 6.0 2500 burb, and I have a couple friends with the same issue

Can you elaborate more about where/how to find a leak from this valley cover? Maybe a pic or illustration?

 

[bottomline2000]

Can you elaborate more about where/how to find a leak from this valley cover? Maybe a pic or illustration?

The center painted section is called a valley cover. You intake sits on top of it. Look at the rear of this cover. Also the same place where your oil pressure sits which is also known to leak. The white connector is plugged into the oil pressure sender. Don't confuse the 2 because an oil pressure sensor is a lot easier to replace than the valley cover.

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[treehan77]

The center painted section is called a valley cover. You intake sits on top of it. Look at the rear of this cover. Also the same place where your oil pressure sits which is also known to leak. The white connector is plugged into the oil pressure sender. Don't confuse the 2 because an oil pressure sensor is a lot easier to replace than the valley cover.

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Ok so to fix a valley cover leak, I would remove that painted section and replace a gasket or is it sealant

 

[treehan77]

Looks like if that’s my leak it’ll be leaking until I need to do knock sensors lol

 

[bottomline2000]

Ok so to fix a valley cover leak, I would remove that painted section and replace a gasket or is it sealant

It's a gasket. I used red RTV sealant to protect the knock sensors from water. Time will tell if it works. The only place sealant is required is the corners of the oil pan where the front and rear plates meet the block.

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[adventurenali92]

Hey guys. Sorry to revive an old tread, but I read through and I have the exact same drops in the exact same place as the OP, on the bottom end of my 2006’s LQ4 6.0. I cant tell where it’s coming from exactly, but when I put my finger up on the oil pan and touch and smell the fluid, it neither looks nor smells like engine oil. I’m so confused! Any help would be appreciated! Should I be worried that it’s a rear main seal or the issue with the valley cover as mentioned above? I did think about the possibility of this fluid being brake or power steering fluid, but I don’t know how to tell if it’s either of those fluids that I’m seeing traveled all the way down there.