Greetings and another oil leak post

[diesel_dave]

Hello everyone, hate to have my introduction be another boring post about a rear engine oil leak, but I'm about at my wits end trying to figure this one out and was hoping someone might have a last ditch piece of advice to save my driveway from getting soaked in oil.

I have probably read every single thread on here that I could find about oil leaks on this generation of engine. From what I read and learned, I have replaced the valve cover gaskets, oil valley pan gasket, oil pressure sensor and yesterday finally did the oil pan gasket. Took it for a drive around the block at 2 am when I was finally finished putting the truck back together after the oil pan gasket replacement anddddd it was still dripping a drop every few minutes from the rear of the oil pan after I parked it. At this point I don't know what to do next. I have looked at the rear main seal several times and it always seems to be dry in that area. What does that leave, just the rear block cover gasket that could be leaking (related to the porosity TSB perhaps)? I'm not a mechanic by any means so I am not sure replacing that is something that I can do in my driveway with the truck up on jack stands. At this point, I'm pretty going to be stuck taking this to a shop to get fixed I'm thinking.

Truck is a 2007 GMC Yukon Denali XL with 225k miles that was only $5,900 (great deal in my area). The engine is very clean inside and pulls very strong. The transmission feels just fine for almost a quarter million miles on it. She has a few little patches of rust that I am going to try and clean up a bit, but besides that seems to be in excellent shape for the age and price. Intended use is to haul around my dogs and pully my 6k pound toy hauler once a month or so. Daily driver is a Tesla Model 3 and my other project is a 2006 M1152 HMMWV.

Completely unrelated, but I also did the motor mounts yesterday and I cannot believe how much of an improvement they made. No more engine vibration at idle and no more drive train clunk when shifting from park to Drive or Reverse or pulling away from a stop. Both mounts were completely obliterated when I removed them with nasty gunk leaking out. Used some cheap ones from Amazon that I had to modify the heat shields on because whoever made them in China doesn't understand basic geometry but they seem to work fine and I expect them or the OEM ones to only last ~50k miles anyways so might as well save money VS the OEM ones (less than half the price).

Thanks in advance for any thoughts.

Edit: I forgot to mention that I replaced the oil cooler blockoff plate seal yesterday when I did the oil pan gasket.

 

[gooffeyguy]

Have you checked the oil cooler block off plate area right above the oil filter? The block off plate gasket can leak and cause a drip towards the rear. Also, there's a screw in plug on the back side of that block that takes an o-ring and that has been known to leak

 

[Geotrash]

Have you checked the oil cooler block off plate area right above the oil filter? The block off plate gasket can leak and cause a drip towards the rear. Also, there's a screw in plug on the back side of that block that takes an o-ring and that has been known to leak

^^^This

 

[diesel_dave]

Have you checked the oil cooler block off plate area right above the oil filter? The block off plate gasket can leak and cause a drip towards the rear. Also, there's a screw in plug on the back side of that block that takes an o-ring and that has been known to leak

Shoot, yes I forgot to add that I did replace that oil cooler block off seal when I did the oil pan gasket yesterday since it was one of the things I read can cause leaks. It didn't look like it was leaking but replaced it anyways. The screw with the o-ring is new to me though. Any more details on this?

 

[davidavidd]

You seem to have covered almost all the possible scenarios, I think it's time to use fluorescent ink. There are leaks that are not visible while there is no oil pressure, the rear main seal is a very problematic area, many times it can appear "dry" because the turbulence generated by the flexplate dissipates small leaks in non-visible areas.

Don't forget to check for other (rare but possible) sources: a faulty oil filter, a loose nut, etc. Sometimes we get caught up in complex repairs and do not give importance to the obvious.

 

[diesel_dave]

You seem to have covered almost all the possible scenarios, I think it's time to use fluorescent ink. There are leaks that are not visible while there is no oil pressure, the rear main seal is a very problematic area, many times it can appear "dry" because the turbulence generated by the flexplate dissipates small leaks in non-visible areas.

Don't forget to check for other (rare but possible) sources: a faulty oil filter, a loose nut, etc. Sometimes we get caught up in complex repairs and do not give importance to the obvious.

The very first thing I tried was fluorescent dye in the oil. Let it run a few minutes while I watched with a UV light anddd nothing. Check it again the next morning and the entire rear of the engine was glowing like a rave club. So, that was less helpful than desired.

I think you have a good point about the rear main though. There is a lot of air movement and centripetal force in there to fling oil away from the center that could be making it appear dry. I think a rear main and maybe the new part number rear block cover might be the next move. I still need to see if it's possible to do this at home but just from looking under the truck, that seems like a pretty big task to do in the driveway so I'll be calling some local shops for quotes.

Anyone know what a "fair" price range would be for a rear main replacement on one of these? I'm thinking ~$1k which really sucks.

 

[OR VietVet]

Rear main seal likely and if you replaced just the seal at the block off plate, you could still be leaking from there. The OE plate is cheap and warps over time. I used a billet plate and fixed a leak I had on my old 02.

 

[Geotrash]

Shoot, yes I forgot to add that I did replace that oil cooler block off seal when I did the oil pan gasket yesterday since it was one of the things I read can cause leaks. It didn't look like it was leaking but replaced it anyways. The screw with the o-ring is new to me though. Any more details on this?

Do you remember what brand of gasket you used for that block-off plate? I normally love Fel-Pro gaskets but the one they make for that spot is a different design than OEM and requires more clamping pressure than the bolts that hold it can deliver. Ask me how I know Anyway, the Dorman gasket is the same design as OEM and works much better.

To R&R the transmission, $1000 is about what I paid for labor when I had a transmission shop put in a new rear main seal and a new torque converter as preventative maintenance. And, if you're going to pay someone to pull that transmission, you might as well replace your TC too, since that's a primary failure mode for the 6L80E, and yours is overdue at that mileage.

 

[diesel_dave]

Do you remember what brand of gasket you used for that block-off plate? I normally love Fel-Pro gaskets but the one they make for that spot is a different design than OEM and requires more clamping pressure than the bolts that hold it can deliver. Ask me how I know Anyway, the Dorman gasket is the same design as OEM and works much better.

To R&R the transmission, $1000 is about what I paid for labor when I had a transmission shop put in a new rear main seal and a new torque converter as preventative maintenance. And, if you're going to pay someone to pull that transmission, you might as well replace your TC too, since that's a primary failure mode for the 6L80E, and yours is overdue at that mileage.

It was a fel-pro metal seal which is exactly what came off of there so it must have been changed previously. That being said, that area is actually bone dry so I'm somewhat sure that's not where it's leaking from. At the moment 90% of the oil leak is over by the starter.

Just got my first quote to replace the rear main for $2,000 which is... eye-wateringly high. I'm hoping that shop just doesn't want to do it and other places will be more reasonable.

 

[OR VietVet]

May be a knock sensor leaking there by the starter area. Your continued oil leak had us all guessing till you finally shared the area/location it was coming from. That is why the knock sensor is now a likely source.

 

[gooffeyguy]

I think the cam sensor is in the back of the motor also

 

[Geotrash]

I think the cam sensor is in the back of the motor also

Close - just to be clear for the OP, it's the crank position sensor that's above the starter. The cam position sensor is in the front cover. And the O-ring on the crank position sensor is indeed a possible leak source.

 

[donjetman]

Hello everyone, hate to have my introduction be another boring post about a rear engine oil leak, but I'm about at my wits end trying to figure this one out and was hoping someone might have a last ditch piece of advice to save my driveway from getting soaked in oil.

I have probably read every single thread on here that I could find about oil leaks on this generation of engine. From what I read and learned, I have replaced the valve cover gaskets, oil valley pan gasket, oil pressure sensor and yesterday finally did the oil pan gasket. Took it for a drive around the block at 2 am when I was finally finished putting the truck back together after the oil pan gasket replacement anddddd it was still dripping a drop every few minutes from the rear of the oil pan after I parked it. At this point I don't know what to do next. I have looked at the rear main seal several times and it always seems to be dry in that area. What does that leave, just the rear block cover gasket that could be leaking (related to the porosity TSB perhaps)? I'm not a mechanic by any means so I am not sure replacing that is something that I can do in my driveway with the truck up on jack stands. At this point, I'm pretty going to be stuck taking this to a shop to get fixed I'm thinking.

Truck is a 2007 GMC Yukon Denali XL with 225k miles that was only $5,900 (great deal in my area).

Thanks in advance for any thoughts.

I paid $8k for our 07 Denali 4 yrs ago w/130k.
Changed the rear main seal on mine almost 4 yrs ago right after I bought it. Believe you me I didn't want to do this BIG TO ME job, but I did. 179k now and still dry as a bone.
Here's the thread: https://www.tahoeyukonforum.com/threads/rear-main-seal-job-pan-etc-07-yukon-denali-6-2.108334/
and more pics: https://www.tahoeyukonforum.com/media/albums/rear-main-seal-oil-pan-etc-day-1.3740/
The other thing that comes to mind is the porous aluminum block TSB. That wouldn't be good.

 

[diesel_dave]

I don't blame you if you don't want to read this massive wall of text so here is the short version: Crank and knock sensors are not leaking at all. Oil cooler blockoff cover is not leaking. Like 99% sure now that it is a leaking rear cover/rear main seal. Several local quotes to replace the rear cover were all around $1,000 so I am going to drive it a bit to get a better idea of the oil consumption and go from there.

---------------------------

So I was finally able to pull myself together after the immense disappointment that it was still leaking after I replaced the oil pan gasket and get back under there to do some more maintenance and try to see if I could see anything new related to the oil leak.

As you guys suggested, I did take a closer look at both the knock sensor and crank position sensors behind the starter but both of those are unfortunately dry. I am still confident the oil cooler block off cover seal isn't leaking because its dry. I took the dust cover and transmission inspection covers off and stuck a borescope in the bellhousing and now I'm leaning much more towards this being a leaking rear cover seal/rear main seal. The flexplate itself appears dry, but everything else in there is pretty moist with grimy oily junk. I can just barely see the top of the rear cover through the holes in the flexplate and it does look wet way up in there. I called a few local auto and transmissions shops and the prices for a full rear cover replacement were $1,000 (local shop), $1,300 (local shop), $1,400 (AAMCO), and finally the hilariously high priced $2,000 local shop quote. Still waiting for one place to call back tomorrow, but I expect it to be in line with the others. I'm beginning to wonder why I spent all that money on engineering school when I could have been charging people $200/hour to work on their cars. Sheesh!

So at this point I think what I am going to do is take the camper out this weekend on a few hundred mile trip and get a better idea how much oil consumption there is going on. If it is less than about a quart per gas station stop, I guess I can deal with that due to the simple fact that it would take ~75k miles worth of driving to break even with buying oil versus having the rear main replaced. Kind of a gamble because if this engine and transmission somehow lasts longer than 300k miles (basically impossible that will be the case), then it would have been cheaper to just have the seal fixed versus topping up the oil every few hundred miles. But, if the engine or transmission gives up the ghost after a few trips pulling my heavy toy hauler, then I'm out ahead because I won't have spent $1,000 only to have to pull the transmission out a few thousand miles later anyways.

If it is taking closer to two or more quarts per gas station stop, then I'll have to get it fixed because that just won't be sustainable long-term.

I ordered a large metal drip tray from Amazon to help save my driveway in the meantime.

Serviced the front and rear differentials this morning. Whoever installed the front differential fill plug must have used red Loctite and a 10 foot breaker bar to tighten that dang thing. By the time I got it out, I had a mountain of various tools accumulated with the secret combo being a heat gun and a huge breaker bar. Torque value is only like 24 ft-lbs on the poor thing! I put a dab of anti-seize on the treads and bead of silicone o-ring lubricant on the seal so I won't have to deal with that in the future. That being said, I noticed that the driver's side CV flange has about 1/8" of wobble in it if you pry on it so I'm guessing I'll be needing a new front differential at some point. I have no idea how it isn't howling or leaking any oil from that seal, but I guess I'll just drive it till it blows.

 

[donjetman]

I don't blame you if you don't want to read this massive wall of text so here is the short version: Crank and knock sensors are not leaking at all. Oil cooler blockoff cover is not leaking. Like 99% sure now that it is a leaking rear cover/rear main seal. Several local quotes to replace the rear cover were all around $1,000 so I am going to drive it a bit to get a better idea of the oil consumption and go from there.

---------------------------

So I was finally able to pull myself together after the immense disappointment that it was still leaking after I replaced the oil pan gasket and get back under there to do some more maintenance and try to see if I could see anything new related to the oil leak.

As you guys suggested, I did take a closer look at both the knock sensor and crank position sensors behind the starter but both of those are unfortunately dry. I am still confident the oil cooler block off cover seal isn't leaking because its dry. I took the dust cover and transmission inspection covers off and stuck a borescope in the bellhousing and now I'm leaning much more towards this being a leaking rear cover seal/rear main seal. The flexplate itself appears dry, but everything else in there is pretty moist with grimy oily junk. I can just barely see the top of the rear cover through the holes in the flexplate and it does look wet way up in there. I called a few local auto and transmissions shops and the prices for a full rear cover replacement were $1,000 (local shop), $1,300 (local shop), $1,400 (AAMCO), and finally the hilariously high priced $2,000 local shop quote. Still waiting for one place to call back tomorrow, but I expect it to be in line with the others. I'm beginning to wonder why I spent all that money on engineering school when I could have been charging people $200/hour to work on their cars. Sheesh!

So at this point I think what I am going to do is take the camper out this weekend on a few hundred mile trip and get a better idea how much oil consumption there is going on. If it is less than about a quart per gas station stop, I guess I can deal with that due to the simple fact that it would take ~75k miles worth of driving to break even with buying oil versus having the rear main replaced. Kind of a gamble because if this engine and transmission somehow lasts longer than 300k miles (basically impossible that will be the case), then it would have been cheaper to just have the seal fixed versus topping up the oil every few hundred miles. But, if the engine or transmission gives up the ghost after a few trips pulling my heavy toy hauler, then I'm out ahead because I won't have spent $1,000 only to have to pull the transmission out a few thousand miles later anyways.

If it is taking closer to two or more quarts per gas station stop, then I'll have to get it fixed because that just won't be sustainable long-term.

I ordered a large metal drip tray from Amazon to help save my driveway in the meantime.

Serviced the front and rear differentials this morning. Whoever installed the front differential fill plug must have used red Loctite and a 10 foot breaker bar to tighten that dang thing. By the time I got it out, I had a mountain of various tools accumulated with the secret combo being a heat gun and a huge breaker bar. Torque value is only like 24 ft-lbs on the poor thing! I put a dab of anti-seize on the treads and bead of silicone o-ring lubricant on the seal so I won't have to deal with that in the future. That being said, I noticed that the driver's side CV flange has about 1/8" of wobble in it if you pry on it so I'm guessing I'll be needing a new front differential at some point. I have no idea how it isn't howling or leaking any oil from that seal, but I guess I'll just drive it till it blows.

here's another thread I did you may be interested in reading: https://www.tahoeyukonforum.com/threads/engine-oil-pan-gasket-change-6-2-yukon-l92.108487/
and a TSB about oil consumption because of stuck rings and poor valve cover pcv design: https://f01.justanswer.com/ebrock63...il+Consumption,+MIL+ON,+Engine+Runs+Rough.pdf

 

[donjetman]

I don't blame you if you don't want to read this massive wall of text so here is the short version: Crank and knock sensors are not leaking at all. Oil cooler blockoff cover is not leaking. Like 99% sure now that it is a leaking rear cover/rear main seal. Several local quotes to replace the rear cover were all around $1,000 so I am going to drive it a bit to get a better idea of the oil consumption and go from there.

---------------------------

So I was finally able to pull myself together after the immense disappointment that it was still leaking after I replaced the oil pan gasket and get back under there to do some more maintenance and try to see if I could see anything new related to the oil leak.

As you guys suggested, I did take a closer look at both the knock sensor and crank position sensors behind the starter but both of those are unfortunately dry. I am still confident the oil cooler block off cover seal isn't leaking because its dry. I took the dust cover and transmission inspection covers off and stuck a borescope in the bellhousing and now I'm leaning much more towards this being a leaking rear cover seal/rear main seal. The flexplate itself appears dry, but everything else in there is pretty moist with grimy oily junk. I can just barely see the top of the rear cover through the holes in the flexplate and it does look wet way up in there. I called a few local auto and transmissions shops and the prices for a full rear cover replacement were $1,000 (local shop), $1,300 (local shop), $1,400 (AAMCO), and finally the hilariously high priced $2,000 local shop quote. Still waiting for one place to call back tomorrow, but I expect it to be in line with the others. I'm beginning to wonder why I spent all that money on engineering school when I could have been charging people $200/hour to work on their cars. Sheesh!

So at this point I think what I am going to do is take the camper out this weekend on a few hundred mile trip and get a better idea how much oil consumption there is going on. If it is less than about a quart per gas station stop, I guess I can deal with that due to the simple fact that it would take ~75k miles worth of driving to break even with buying oil versus having the rear main replaced. Kind of a gamble because if this engine and transmission somehow lasts longer than 300k miles (basically impossible that will be the case), then it would have been cheaper to just have the seal fixed versus topping up the oil every few hundred miles. But, if the engine or transmission gives up the ghost after a few trips pulling my heavy toy hauler, then I'm out ahead because I won't have spent $1,000 only to have to pull the transmission out a few thousand miles later anyways.

If it is taking closer to two or more quarts per gas station stop, then I'll have to get it fixed because that just won't be sustainable long-term.

I ordered a large metal drip tray from Amazon to help save my driveway in the meantime.

Serviced the front and rear differentials this morning. Whoever installed the front differential fill plug must have used red Loctite and a 10 foot breaker bar to tighten that dang thing. By the time I got it out, I had a mountain of various tools accumulated with the secret combo being a heat gun and a huge breaker bar. Torque value is only like 24 ft-lbs on the poor thing! I put a dab of anti-seize on the treads and bead of silicone o-ring lubricant on the seal so I won't have to deal with that in the future. That being said, I noticed that the driver's side CV flange has about 1/8" of wobble in it if you pry on it so I'm guessing I'll be needing a new front differential at some point. I have no idea how it isn't howling or leaking any oil from that seal, but I guess I'll just drive it till it blows.

And here's what my spark plugs looked like: https://www.tahoeyukonforum.com/threads/sparkies-no-beno.108579/

 

[AngryFish]

If it looks like the rear main leaking, but the rear main is good, then it's probably the cover gasket. The rear main seals to the rear cover, and the rear cover has a gasket to the block. There are two oil galleries at the top that are connected and sealed by this gasket, and the rear cover acts as part of the channel.

I had a really bad leak that was coming from the back, but above the oil pan and not the rear main. L59 engine. They replaced the rear main while they were there, but the cover gasket had cooked by the heat and failed at approximately 287,000 and 8500 engine hours.

Not sure that this is the right part for your engine, but check P/N 1263 9250

 

[Geotrash]

They replaced the rear main while they were there, but the cover gasket had cooked by the heat and failed at approximately 287,000 and 8500 engine hours.

What a piece of crap! Couldn't even make 300,000 miles!

 

[diesel_dave]

If it looks like the rear main leaking, but the rear main is good, then it's probably the cover gasket. The rear main seals to the rear cover, and the rear cover has a gasket to the block. There are two oil galleries at the top that are connected and sealed by this gasket, and the rear cover acts as part of the channel.

I had a really bad leak that was coming from the back, but above the oil pan and not the rear main. L59 engine. They replaced the rear main while they were there, but the cover gasket had cooked by the heat and failed at approximately 287,000 and 8500 engine hours.

Not sure that this is the right part for your engine, but check P/N 1263 9250

I think we are both on the exact same page because I don't really see oil wetting around the rear main seal itself. Just general oiliness around the periphery of the rear cover but its pretty hard to see through the transmission inspection hole. All of the shops I called said they replace the rear cover when they do a rear main seal because they get it all as a kit like that so, if I decide to move ahead with the $1k repair on a truck that only cost me $6k, that should fix the leak. I took my camper on a 100 mile drive up in the mountains today and the truck did so much better than I was expecting that I am a little more inclined to get it fixed whereas before, I wasn't sure the truck was up to the task of pulling my relatively heavy toy hauler.

 

[LordWayback]

The very first thing I tried was fluorescent dye in the oil. Let it run a few minutes while I watched with a UV light anddd nothing. Check it again the next morning and the entire rear of the engine was glowing like a rave club. So, that was less helpful than desired.

I think you have a good point about the rear main though. There is a lot of air movement and centripetal force in there to fling oil away from the center that could be making it appear dry. I think a rear main and maybe the new part number rear block cover might be the next move. I still need to see if it's possible to do this at home but just from looking under the truck, that seems like a pretty big task to do in the driveway so I'll be calling some local shops for quotes.

Anyone know what a "fair" price range would be for a rear main replacement on one of these? I'm thinking ~$1k which really sucks.

If you’re gonna do a rear main seal I’d get the transmission upgrades done so it’ll never quit.