Not Sure If Your Rear Main Seal Is Leaking?

[JonnyTahoe]

If you have oil dripping off all these spots under your Truck your rear main or rear main plate is probably leaking.

 

[fasteddy]

Yup
Been there.
It can also be the oil pressure sensor (less seldom) which is at the top rear of the block.

Oil looks fresh though. And oilpan and bellhousing and bolts look very clean.

 

[OR VietVet]

Maybe even the engine oil cooler line at the plate or the block off plate if no oil cooler lines.

 

[mattbta]

Crazy timing. Here's mine this weekend after blasting it clean with brake cleaner. Started it up and saw this: (It's either rear main seal/cover or I did a bad job on the oil pan gasket or BOTH) Thoughts? All new stuff within a year: Oil Pressure Sensor, Camshaft Position Sensor, Crankshaft Position Sensor, Oil Pan Gasket, Valley cover Gasket, new Blockoff Plate.

 

[wildcatgoal]

If you replaced the oil pan gasket and it still leaks, then consider the RMS. Don't go doing a RMS before replacing (properly) the oil pan gasket.

And when you do replace the oil pan gasket, you need to put sufficient dabs of RTV at all 4 corners front and back where the block has splits. If you don't, it'll leak. Stupid design, frankly, to have a pan gasket seal over a split surface. Absolute dumbassery. Lots of people don't do that RTV part right.

When you do replace the RMS, you can fix the RTV from the top of the installed oil pan and seal it up again (you have to, anyway).

 

[JonnyTahoe]

I like your aftermarket block-off plate. The leaking of these engines in one of the most annoying issues. Your way ahead of me with all that you have replaced so far.

 

[mattbta]

I had a shop replace the oil pan gasket a couple years ago and still had a small drip. During lockdown, I pulled the oil pan to look for sludge as I replaced my Castech heads so I put a new gasket on then. The leak has gone from a few drops to totally soaking cardboard underneath it after a drive or two. I could always do the gasket again as it's fairly easy with 2WD. I'm really sick of it though so I'm about to go drastic and have a dealer look at it. I've got a SacCity Vette barbell to go in when it gets pulled, too.


EDIT: Don't mean to hijack your thread. Just looking for opinions as well, our's looks pretty much the same as far as where the leak shows up.

 

[JonnyTahoe]

I had a shop replace the oil pan gasket a couple years ago and still had a small drip. During lockdown, I pulled the oil pan to look for sludge as I replaced my Castech heads so I put a new gasket on then. The leak has gone from a few drops to totally soaking cardboard underneath it after a drive or two. I could always do the gasket again as it's fairly easy with 2WD. I'm really sick of it though so I'm about to go drastic and have a dealer look at it. I've got a SacCity Vette barbell to go in when it gets pulled, too.


EDIT: Don't mean to hijack your thread. Just looking for opinions as well, our's looks pretty much the same as far as where the leak shows up.

Sounds like mine exactly I get my cardboard from Costco and it comes in handy for cleaning parts too. I will be doing the oil pan this week but I already know that's not it. It leaks for hours after you turn the engine off and the oil is not over the top of the oil pan when the engine is not running.

 

[Greg Kulbick]

I was just under our Tahoe Friday night trying to clean up under there and pinpoint where the oil is coming from. I think the block off plate is fine. I didn't see much of anything when looking through the hole in the bellhousing, so I'm keeping my fingers crossed its just the pan gasket.

 

[mattbta]

@Larryjb -- did yours look like this?

 

[Larryjb]

@Larryjb -- did yours look like this?

Hmm, look like what? Do you mean your previous picture from May 10?

The only way I was able to conclude that my rear main was leaking was to replace the oil pan gasket (which I knew was leaking) by the book. I did everything by the book: specified RTV at the corners, torqued everything exactly as instructed, etc. I cleaned the gasket surfaces very carefully so as to not score the mating surface. I had found a ridge which I smoothed off, and added a dab of RTV to.

When I still had a leak, I figured it had to be the rear main. Unless you have a really good boroscope, there is no way you can see well enough behind the flexplate. You won't be able to properly see all the rear main cover and rear main. Once I got my tranny out, I could clearly see where things had been leaking, and the worst leaking was in fact the rear cover.

If you leak is worse after doing the oil pan, you may want to redo it making sure everything is done by the book. Somewhere I do have a thread on this, but I can't remember if it was with my rear main oil seal thread or not.

Good luck!

 

[mattbta]

Yeah, both jonnytahoe and my pictures.

The cheapo amazon special camera I used a year ago was worthless. I can't pinpoint exactly when it got worse but this was the second or third time I dropped the pan (new gasket every time) and i used copious RTV. Guess I'll just take it in for diagnosis/repair as I have zero interest in pulling the transmission myself. Thanks for documenting your journey on all of these things though.

 

[OR VietVet]

Yeah, both jonnytahoe and my pictures.

The cheapo amazon special camera I used a year ago was worthless. I can't pinpoint exactly when it got worse but this was the second or third time I dropped the pan (new gasket every time) and i used copious RTV. Guess I'll just take it in for diagnosis/repair as I have zero interest in pulling the transmission myself. Thanks for documenting your journey on all of these things though.

Too much, "copious", RTV is bad and causes problems with oil pick up. Needs just a dab here and there in just the right places. I think I know what you were saying but wanted to say it for other members who have not had the fun of replacing the oil pan gasket.

I just did them both at the same time. No doubt I got all leaks. While under there for the work I am doing in my build/construction thread, I can see nothing but dry. Well, that and all the new parts I am bolting on.

 

[JonnyTahoe]

Yeah, both jonnytahoe and my pictures.

The cheapo amazon special camera I used a year ago was worthless. I can't pinpoint exactly when it got worse but this was the second or third time I dropped the pan (new gasket every time) and i used copious RTV. Guess I'll just take it in for diagnosis/repair as I have zero interest in pulling the transmission myself. Thanks for documenting your journey on all of these things though.

Nobody could have much interest in removing the trans themselves but being able to do it yourself gives a person much satisfaction being it is one of the most time consuming and labor intensive jobs you will ever do to your Truck.

 

[OR VietVet]

Hip Hip Hooray for transmission jacks.

 

[mattbta]

Hip Hip Hooray for transmission jacks.

And lifts.

 

[Larryjb]

Nobody could have much interest in removing the trans themselves but being able to do it yourself gives a person much satisfaction being it is one of the most time consuming and labor intensive jobs you will ever do to your Truck.

Yup, and no leaks 1 year later

 

[Larryjb]

And lifts.

And done without a lift!

 

[Larryjb]

Yeah, both jonnytahoe and my pictures.

The cheapo amazon special camera I used a year ago was worthless. I can't pinpoint exactly when it got worse but this was the second or third time I dropped the pan (new gasket every time) and i used copious RTV. Guess I'll just take it in for diagnosis/repair as I have zero interest in pulling the transmission myself. Thanks for documenting your journey on all of these things though.

Also, where exactly did you use the RTV? What RTV did you use? (Did you use the one with maximum oil resistance?)

 

[Larryjb]

... I have zero interest in pulling the transmission myself. ....

Ah, come on.... It puts hair on your chest! (unless you chafe it off trying to maneuver the transfer case... That sucker was heavy even with it's magnesium case....)