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.