Help me find this oil leak please!

[John03Z71]

So I spent over an hour last night getting dirty trying to find the leak with zero luck.

First thing I did was pull the starter off, since I dried everything up the night before and the very first drips started forming on the starter bolt closest to the block. Crankshaft position sensor appears dry, and I really couldn't see any significantly wet areas above the starter which really puzzled me considering the amount of oil that is dripping from this area. The flywheel was dry, so does this mean my rear main should be fine?

Second, I pulled the plastic engine cover off and reached around the back of the block on both sides to feel around, elbow deep, hoping I could feel some oil around the oil pressure sensor but couldn't feel anything significantly wet, just pulled back some greasy gritty fingers.

I'm totally stumped on this one. I plan to bring it in to a local independent shop this afternoon that has great reviews, so hopefully they can help me find this leak, it's driving me nuts.

I got optimistic for a minute because I noticed my oil dipsick is broken off from the mounting bracket at the top of the engine just below the yellow ring, which is also giving it some play around the area where it enters the block down low. I noticed some shiny wet oil around that entrance, but wiped it dry with the engine running and nothing was coming out but the steady fast oil drips kept falling from the starter bolt. sigh......

 

[Doubeleive]

your oil dipstick seal can leak, since it's broke of you may want to go ahead and replace it to rule it out, mine leaked before on my nbs but it wasn't a real bad leak

 

[Erickk120]

Pictures would have been nice, I haven't gotten the patience to do my rear main seal and cover gasket yet, I have the same area around the starter wet and drips, and also have a drip for around my drain plug that is coming from somewhere above, then that oil travels through the oil pan down to the middle of it and it drips into my transmission lines that go to the radiator, making it appear as if its the oil pan gasket, which I did replace and half of it is clean the other half of it is covered in oil, but I know its just coming from the rear upper section on the engine and traveling down over time, My inspection cover looks clean and no oil inside of the flywheel area from what I can see, but everything else is dry, deep inside I just know its the rear seal/cover gasket but it doesn't really show it's coming from there. Its one of those deceiving oil leaks that give you false hope, but I know better At least mine only needs half a quart after several months. If it was as bad as yours I would be seriously worried and would be taking care of it ASAP!

 

[Doubeleive]

Pictures would have been nice, I haven't gotten the patience to do my rear main seal and cover gasket yet, I have the same area around the starter wet and drips, and also have a drip for around my drain plug that is coming from somewhere above, then that oil travels through the oil pan down to the middle of it and it drips into my transmission lines that go to the radiator, making it appear as if its the oil pan gasket, which I did replace and half of it is clean the other half of it is covered in oil, but I know its just coming from the rear upper section on the engine and traveling down over time, My inspection cover looks clean and no oil inside of the flywheel area from what I can see, but everything else is dry, deep inside I just know its the rear seal/cover gasket but it doesn't really show it's coming from there. Its one of those deceiving oil leaks that give you false hope, but I know better At least mine only needs half a quart after several months. If it was as bad as yours I would be seriously worried and would be taking care of it ASAP!

when you look inside the inspection plate you will want to look with a flashlight deep inside behind the very bottom of the flywheel, so basically "bottom center" if the rear main is leaking at all that is where you will see oil, if you cant get the right angle a small mirror will work they sell those telescoping angle mirrors at the autoparts store for like $2-3

 

[John03Z71]

Thanks all. Had it diagnosed by a very reputable shop today as the rear main seal. Sucks......

 

[Notorious Big T]

I have a 2003 Tahoe 5.3L Z71. I've developed a very bad oil leak over the past several months. It started out as a moderate leak, having to add a quart every month or two, but recently has been leaving a couple softball size circles when parked and I have to add a quart every 5 days or so as the check oil level light comes on this fast... so I took it in to a reputable shop and they said it was my oil pan gasket. $400 later I'm out the door and drive home about 30 miles, park it, come out later that evening and see more large oil spots under the truck. Pissed.

I called the shop and they said there was so much oil under there that they had to clean up (true story) that it was hard to tell exactly where it was all coming from, but the pan gasket was definitely leaking, as well as the oil cooler block off plate gasket (both replaced). He insisted that those were the two main culprits, and explained to me that since those were leaky and now sealed up, the increased "pressure" is likely causing oil to be forced out of other areas that were also leaking, but only slightly before the new pan gasket and block off plate gasket. This sounds logical, however part of me is thinking they just didn't take the time to properly diagnose and find all my leaks. In fact it's leaking worse now than when I brought it in and had the pan gasket and block off plate gasket done. He also mentioned my rear main seal is leaking as well as my timing cover gasket, but to just "keep an eye on them for now". Hard to "just keep an eye" on oil levels when I leave the shop and 5 days later the check oil level light comes on!

Last Thursday the check oil level light came on, so I dumped a quart of oil in along with about 10oz of Bar's Stop Leak which was recommended by the shop. Fast forward to yesterday, on my lunch break I hopped in and am greeted with "check oil level" on the dash... I hopped out and took a peak underneath, and there is a steady drip coming down almost like a drippy faucet. I top it off and drive home, then I crawled under there last night and spent about 30 mins wiping / drying everything up real good because I wanted to pinpoint the leak. Once dry, I cranked it up and crawled under it with a flashlight right away. After about 15 seconds, the first sign of oil came down from the starter bolt on the side closest to the block. This quickly turned into the leaky faucet type leak, it was dripping a drop of oil at least every 2-3 seconds. After about a minute, it started running over to the other side of the bellhousing and dripping off one of those bolts, which then began dripping down the bellhousing area where the engine and transmission meet, creating what APPEARED to be a rear main seal leak. I popped off the inspection cover on the bellhousing (after shutting engine off) and it was dry as a bone, good sign right?

I continued to let it run for about 5 minutes and the area above the starter appears to be the only origin of this horrible leak, again dripping constantly every couple seconds. It was late and I didn't have time to pull the starter, so my question is what is above the starter that could be causing this bad of a leak? I replaced the oil pressure sensor about 3-4 years ago, and also reached my finger way back there to check if it was wet and leaking down the engine to that area and while there was some grease around it, it did not feel terribly wet back there so I'm not convinced it is the culprit due to the significant volume of oil that is leaking out. I've heard the rear main is generally a slow leak, so since the flywheel is dry behind the inspection plate and there wasn't any oil leaking directly between the engine and transmission I'm hoping it's not the rear main.

Sorry for the long post but I wanted to provide as much detail as possible. Any helpful info that would assist me in pinpointing this bad leak coming from above the starter would be much appreciated!

My 97 Burban had-bad power steering-leaks


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[Erickk120]

Thanks all. Had it diagnosed by a very reputable shop today as the rear main seal. Sucks......

Well, that is unfortunate, that will be a good dent in the wallet to fix.

 

[Steve A]

I'm guessing you'll have it done, so have them change the front seal on the transmission while it's out.

 

[Bill Hayes]

I had a bad oil leak on my 2007 z71. Changed rear main seal and the pan started leaking. Couple days later I discovered the pcv valve is built inside the driver side valve cover. It was stopped up. Replaced the cover and the leaks stopped.

 

[John03Z71]

I'm guessing you'll have it done, so have them change the front seal on the transmission while it's out.

Just had the rear main seal job finished up this morning. My BAD oil leak is gone (the drop every couple seconds off the starter and where bellhousing meets oil pan), now it’s just leaking a drop every minute or two from the same place, so am glad the rear main solved the bulk of the leak.

When we had the transmission pulled back I could still see some wet oil spots up higher on the (passenger side) engine so I’m thinking about trying the pressure sensor, again (did it about 4 yrs ago due to gauge reading bad). Valve cover gasket appeared to be seeping again a tad as well, did those around the same time as the pressure switch. But whatever is still dropping a drop of oil every minute or so has got to be the oil pressure sensor, cam position sensor, or valve cover gasket. What exactly, and where, is the “valley pan” gasket???