Rear main seal or oil pan leak?

[Mr T]

Folks:

2008 Denali XL, 165,000 miles. Original trans, motor and other majors, but lots of repairs in other areas (lift gate, auto ride, 2 sets of cats, door hinges, etc).

I noticed 1 or 2 drips of oil a day on my garage floor. Got under it to take a look. Small oil accumulated between motor and trans. Clearly its engine oil, by the way. I thought it would be the rear main seal; however, a mechanic friend said on and 08 with that many miles, more likley the oil pan leaking and rear main seal.

2 questions: 1) Is there a sure way to know which of the two is leaking? 2) What has been your experience with leaks in this area?

Thx.

TKH

 

[JollyRoger01]

It's a pretty decent mix of the rear seal and pan, but I personally have replaced more rear seals/cam cover gaskets than pan gaskets. If you get the part from Chevy it will come with a new rear seal, housing, housing gasket and bolts for around $50.

 

[Brian Wilson]

most rear main leaks are caused by pcv valve being clogged building pressure in the crankcase. be sure to check that before you dive into replacing the seal

 

[Bowana]

There is also a TSB for 07-14 LS engines regarding porisity in the engine block and or the cover over the back of the engine where the crank seal is located. I do not have the link handy or I would post it. I have the same leak on my 2010 6.2 and although the oil is leaking out the metal housing behind the engine, it is impossible to tell where the leak originates unless you pull the drive shaft and transmission along with the pressure plate. The install time for the new metal gasket is only .50 hours and if the block is leaking you add rtv silicone to where it is sweating and then replace the metal housing with gaskets as well. Whole labor is approx 8 hours plus parts. You may consider placing a piece of cardboard on the floor instead.

 

[CrashTestDummy]

The oil pressure gauge sending unit is on the upper back side of the engine. Make sure it’s not leaking before you blame the RMS.

 

[vmoua509]

i am also chasing the mysterious oil leak coming from between the engine block and the transmission. I have an 07 denali xl 6.2L 189k. here is the tsb that I found about it:

Subject: 5.3L LC9, LS4, L33, LH6, LM4, 5.7L LS1, LS6, 6.0L LS2, L76, 6.2L L92, 7.0L LS7 - EngineOil Leak at Rear Cover Assembly Area (Engine Block Porosity RTV Repair Procedure) #05-06-01-034E - (02/12/2007)

Models: 2004-2007 Buick Rainier
2005-2007 Cadillac CTS-V
2007 Cadillac Escalade, Escalade ESV, Escalade EXT
2003-2007 ChevroletCorvette, TrailBlazer
2004-2006 Chevrolet SSR
2005-2007 Chevrolet Silverado, Silverado SS
2006-2007 Chevrolet Impala SS, Monte Carlo SS, TrailBlazer SS
2007 Chevrolet Avalanche, Suburban, Tahoe
2003-2007 GMC Envoy, Sierra
2004-2005 GMC Envoy XUV
2007 GMC Yukon XL, Yukon Denali, Yukon XL Denali
2004-2006 Pontiac GTO
2005-2007 Pontiac Grand Prix GXP
2005-2007 Saab 9-7X
with 5.3L, 5.7L, 6.0L, 6.2L, 7.0L VORTEC™ GEN III or GEN IV V8Engine (RPOs LC9, LS4, L33, LH6, LM4, LS1, LS6, LS2, L76, L92, LS7)
--------------------------------------------------------------------------------
This bulletin is being revised to update warranty information. Please discard Corporate Bulletin Number 05-06-01-034D (Section 06 -- Engine/Propulsion System).
--------------------------------------------------------------------------------
Condition
Some customers may comment on an engineoil leak.

Cause
Upon initial diagnosis, it may be determined that the leak is coming from the rear cover gasket. This condition may be caused by engine block porosity on the sealing surface. This issue pertains to aluminum block applications only.

Correction
Follow the steps for Oil Leak Diagnosis in SI to determine the source of the leak. If the leak has been diagnosed as coming from the engine rear cover assembly, refer to Engine Rear Cover Replacement in SI and remove the engine rear cover assembly. Inspect for engine block porosity where the engine rear cover mates to the engine block. If porosity is found anywhere on the sealing surface, use the following procedure to apply RTV to repair the engine block porosity. Refer to the illustration below.

Important: Clean any residual oil from the block and cover before applying the sealant in the next step.

Wipe a small amount of RTV, P/N 12378521 (in Canada, use P/N 88901148), onto the surface using a plastic scraper to fill the porosity.
Remove any excess RTV material, especially from inside the high pressure oil passage. Refer to #1 in the above illustration.
The joint may be closed immediately after applying the RTV. Total joint time after the RTV has been applied must be under 20 minutes.
Important: Refer to Engine Rear Cover Replacement in SI and follow the tightening specifications and sequence.

Reinstall the engine rear cover using a new gasket and a new crankshaft rear main seal. Refer to Engine Rear Cover Replacement in SI.
Parts Information
Important: For Saab (U.S.) only, use P/N 12345795, EngineOil Dye (U.S.), or equivalent.

Part Number
Description
Qty

12574293
Gasket - Crankshaft Rear Oil Seal Housing
1

89060436
Seal, Crankshaft Rear Main
1

12378521 (U.S.)
88901148 (Canada)
Sealant
1

12345795 (U.S.)
Dye, EngineOil
1

10953470 (Canada)
Dye, EngineOil
1

Warranty Information
Excluding Saab U.S. Models
For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
J7510*
Oil Leak -- Rear Cover Area -- Porosity Repair

CTS-V
5.5 hrs

Corvette
- M/T
- A/T
5.9 hrs
5.4 hrs

SSR
5.4 hrs

TrailBlazer/Envoy/Rainier/Saab 9-7X (Canada)
- 2WD
- 4WD
5.7 hrs
6.5 hrs

GTO
- M/T
- A/T
10.2 hrs
10.5 hrs

Grand Prix/Impala/Monte Carlo
5.7 hrs

Silverado//Sierra Models
- M/T
- A/T
4.5 hrs
5.5 hrs
Avalanche, Escalade, Suburban, Tahoe, Yukon Models
4.5 hrs
Add
With skid plate
0.2 hr
With HP2**
0.5 hr
To clean parts over 48,000 km (30,000 mi)
0.1-0.3 hr

* This labor operation is for bulletin use only. It will not be published in the Labor Time Guide.
** HP2 Hybrid Propulsion Electric, AHS2

Saab U.S. Models
For vehicles repaired under warranty, use:

Labor Operation
Description
Failed Object
Fault/Reason Code
Location Code
Warranty Type
Repair/Action Code
Labor Time
2161901
Replace part, Seal, End PlateV8 T-Truck
21619
57
0
01
01
6.5 hrs
Add
9821001
R&R Anti-Submarine (Skid) Plate 0.2 hr

Add
To clean parts over 48,000 km (30,000 mi)
0.1 to 0.3 hr in 99 time

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION
© Copyright General Motors Corporation. All Rights Reserved

 

[Truestyle Scott]

07 ESV. 2 years ago at 93k miles I changed the oil pan gasket which was a 6 hour task but I got it done and it has sealed up my truck ever since. I kind of guessed thats what was leaking and I guessed right. I did everything to spec, I used the AllData instructions and a good felpro gasket.

Now I have a similar leak that is leaving a quarter size puddle every night. Whole back of the engine on the bottom is covered in oil, both sides. Im aware of all the things that can leak but not on how to check which one it is.

I saw maybe some seepage around the valve covers so I changed the gaskets, wasnt too hard but didnt fix the leaks on the floor. I saw a little oil around that oil cooler block off, that was cheap and easy to fix but didnt affect the oil leak. There are only 3 other possibilities, rear main cover, oil pan or oil sensor. From the transmission bellhousing inspection cover i can see inside and stick my finger in there and there is no oil in it so I think Im safe to say its not the rear main cover. Next is the oil pan gasket, which I want to believe isnt possible to be leaking again since I did everything to spec and its only been 2 years 20,000 miles. Lastly would be the oil sensor behind the intake. I cant see for shit the back of the motor or even get my hand back there to know if its leaking. How can you tell if its leaking? On older 5.3s the sensor will go back and leak. My oil pressure has been fine as far as i know, is it still possible its leaking? Do they leak around 113k miles? What is a way to see if its leaking? Its not an easy fix so i want to make sure its leaking. Sort of hoping its leaking, probably easier than doing an oil pan again. Any advice appreciated.

 

[Iron Head Eddie]

Folks:

2008 Denali XL, 165,000 miles. Original trans, motor and other majors, but lots of repairs in other areas (lift gate, auto ride, 2 sets of cats, door hinges, etc).

I noticed 1 or 2 drips of oil a day on my garage floor. Got under it to take a look. Small oil accumulated between motor and trans. Clearly its engine oil, by the way. I thought it would be the rear main seal; however, a mechanic friend said on and 08 with that many miles, more likley the oil pan leaking and rear main seal.

2 questions: 1) Is there a sure way to know which of the two is leaking? 2) What has been your experience with leaks in this area?

Thx.

TKH

I just saw this post looking for something else and i figure by the date it was made that you have resolved your issue; with that being said I want to save other people a lot of trouble. I had the same issue, oil dripping out between the block and bell housing. I did the rear main and it did not resolve it, wasted $1,200. There is an oil pressure sending switch on the back of the 6.2 that can break to leak, you can replace them that hard way or the easy way. It’s behind the intake plenum, I did it thebhard wa by cramming my hand back there and swapping it. That also wasn’t the fix, turns out it was simply my oil fill neck o ring. The oil was leaking from the filler neck, running along the lifter valley plate and down the back of the block. Before finding this I decided to do all my upper seals and gaskets. I’m about $2,000 deep now into a $3 o ring that can be replaced without even removing the neck. Hope this helps

 

[02Lightning]

I just saw this post looking for something else and i figure by the date it was made that you have resolved your issue; with that being said I want to save other people a lot of trouble. I had the same issue, oil dripping out between the block and bell housing. I did the rear main and it did not resolve it, wasted $1,200. There is an oil pressure sending switch on the back of the 6.2 that can break to leak, you can replace them that hard way or the easy way. It’s behind the intake plenum, I did it thebhard wa by cramming my hand back there and swapping it. That also wasn’t the fix, turns out it was simply my oil fill neck o ring. The oil was leaking from the filler neck, running along the lifter valley plate and down the back of the block. Before finding this I decided to do all my upper seals and gaskets. I’m about $2,000 deep now into a $3 o ring that can be replaced without even removing the neck. Hope this helps

This is the o-ring between the valve cover and filler neck? How do you replace without removing the neck?