Hello guys, I hope someone can help me with this. My daily 06 Suburban 2500 has developed a leak I can't seem to pinpoint. Last year I replaced the oil pan because I had some drips on the bottom. Last oil change in May or June I recall seeing a bit more drips, but didn't think much of it. Truck is stock w/ 253k and I bought it w/ 225k.

Within the last month it's been leaking more. The starter has drips and drips down the bell housing and oil pan. I removed the inspection cover of the transmission and it doesn't seem like it's the rear main. The flexplate and torque converter are both dry. The outside of the bell housing (on the firewall side), however, is wet, and the crossover exhaust pipe has some oil stains.

I tried a borescope, but couldn't see if the camshaft position sensor or pressure sender was leaking. I removed the intake and looks like the valley cover may be the culprit? Looked pretty gunky, so I cleaned it up and got a new gasket. When I loosened the 13 mm bolts it seemed like maybe 2 were loose. Can that much oil leak from that seal? The cover had a bit of oil on the edge on the mating surface.

I've been seeing some videos but they are mostly saying it's a common thing on the Gen IV.

 

It’s the rear main

 

Wouldn't that cause the flexplate to have oil? It's pretty dry inside there. I checked with engine running. At this point I thought maybe there's multiple leaks, and decided to start with the top and work my way down.

I got me some UV leak detection dye. The kids at the local AutoZone said they'd never heard of such thing! Luckily the manager found it in the back.

If it is the rear main seal, I'll have to do it over the long weekend. What is that tool needed to align the cover? The generic aluminum tool from Amazon should be fine, right?

 

I'd suspect the oil pressure sending unit or the cam position sensor. The CPS O-ring is about 4" below the valley cover and is known to fail.



You can see how deep down it goes before it gets to the O-ring, and how if it leaks, it's going to go inside the BH.

 

Thank you. At least from the top of the sensor I did no see any fresh oil. But forgot that o ring is way down there. I'll check it with an inspection mirror since I haven't reinstalled the intake.

Question: do I need to do a relearn if I change that sensor? I don't have a scanner that will do that, just a basic handheld that reads codes.

 

My rear main was exactly like yours oil everywhere but in the trans. If you look up through the weep hole at just the right angle after applying UV dye you may see oil. I promise you it is a rear main, you have the exact leak I did.

I use a block of wood and a mallet. SacCity Corvette sells the alignment tool iirc

 

I wouldn't think so, but what do I know. Wouldn't hurt even if not strictly "necessary". Regardless, just changing the O-ring shouldn't bother it, if you keep the same sensor, and it goes back in right where it came out from.

 

Thanks. I went ahead and changed the cam sensor. When I pulled it out there was definitely oil ABOVE the o-ring. Knock sensor connectors broke when I pressed them to release them, and sensors themselves had a bit of rust. Luckily I had new sensors and new wiring harness from my 99 Silverado that I never installed.

I put everything back together and she started right up. No issues. The hard tube for the PCV broke, so I taped it up with electrical tape. :-(

I put that UV dye in the oil. So I'll be checking on it on the next few days.

It's starting to look like everything is leaking! LOL

 

Try using a piece of heat shrink wrap.

 

Well darn. This morning I took the kids to school and I had steam coming from the tailpipe. I figured it would go away, but it didn't. I had to go back home to drive my 99 to work. I could smell a bit of a sweet smell. Drove about 6 miles and it wasn't overheating or missing; it seemed to drive just fine.

The only thing I did was remove the little coolant hoses under the throttle body, then added about 1/2 gallon of the water that had lost. Yesterday I let it idle like 10 minutes and it was just fine. The throttle body can't leak coolant into the intake, can it? Otherwise I can't imagine what's going on.