Oil leak..but from where?

FL2500 · Sep 10, 2014

Abbreviated story:
2003 5.7 4x4. Replaced motor, runs great except it was leaking oil from the bell housing area pretty bad. As it turns out I had forgotten to apply black RTV to the 4 points required. Today I took the pan off, new gasket assembly, black RTV and back together it went. Well... same thing.. if idling it drips a tablespoon or more every 5 minutes so it is significant.

I looked all over, my best guess is that it is coming out of the dipstick tube insertion point somehow and running over the side of the block and down to the rear of the oil pan? I have the inspection plate off, and if it was the rear main it would be pretty obvious right? There is no oil slung all over the TC.

There are a few pictures to help anyone who may be able to give some advice, the area in red is where the oil seems to be traveling along. Any and all assistance very appreciated. Thanks.

Redtruck-VA · Sep 10, 2014

I had a similar leak, it was coming from the rear of the driverside valve cover.

RonJon '06 · Sep 10, 2014

I have the same leak after rebuilding mine. Originally I put only a very small amount of black RTV at the front cover/block/oil pan junction and it leaked really bad when I first started it up. I had to take off the front cover for something else and while it was off I dropped the pan, cleaned the junction and added more RTV. Now it's a lot better but still leaks and definitely more on one side than the other. I'm guessing I just have to go back again and use even more RTV.

FL2500 · Sep 10, 2014

Checked up top and no leaks look to be occurring up there. This is the most frustrating thing because it is so not obvious where its really coming from. When I put the dipstick back in there was no o-ring of any sort and I could not find a reference to one. Is there supposed to be one and if I left it out would it cause this sort of oil leak? Thank you all.

FL2500 · Sep 10, 2014

RonJon '06 said:
I have the same leak after rebuilding mine. Originally I put only a very small amount of black RTV at the front cover/block/oil pan junction and it leaked really bad when I first started it up. I had to take off the front cover for something else and while it was off I dropped the pan, cleaned the junction and added more RTV. Now it's a lot better but still leaks and definitely more on one side than the other. I'm guessing I just have to go back again and use even more RTV.

How much is enough? I laid a 1.5 inch long strip on all 4 places and fairly thick too.

RonJon '06 · Sep 10, 2014

FL2500 said:
How much is enough? I laid a 1.5 inch long strip on all 4 places and fairly thick too.

When I took the oil pan off in the first place it looked like there was only a small amount at the front cover/ block from the factory. The last time I used a dab about the size of a nickel on each side.

The oil dipstick is supposed to have an O-Ring, mine did. It goes in the groove about 1/2" inch from the end. If your leak is only on that side and not further forward then I would think that's it.

crazzywolfie · Sep 10, 2014

maybe you snugged the bolts up too soon. did you let the rtv set up for a couple hours before you snugged up the bolts? that step usually takes a lot of patient but makes a huge difference to whether you leak or not

RonJon '06 · Sep 10, 2014

crazzywolfie said:
maybe you snugged the bolts up too soon. did you let the rtv set up for a couple hours before you snugged up the bolts? that step usually takes a lot of patient but makes a huge difference to whether you leak or not

In my case I did on the transmission pan but maybe not on the oil pan, at least not for very long. I'll definately try that next time.

FL2500 · Sep 10, 2014

Thank you.

I let it sit for 30 minutes, hope that was enough. No o-ring on mine so that may well be it. I cant find anything with my google skills to say if leaving that out would cause this sort of oil leak or what the part number of that o-ring is.

I bought a UV dye kit, but have never used one before, may have to resort to it though.

crazzywolfie · Sep 10, 2014

i am pretty sure on the RTV instructions it says to let it setup for about and hour before you tighten your bolts all the way down. i know i learned this lesson on my thermostat housing. had to do it twice but the second time i took my time and let it setup and so far no leaks.

FL2500 · Sep 11, 2014

Before I go and do this again, I will try out this UV dye kit. Will know whats what for sure soon, thanks.

FL2500 · Sep 11, 2014

Ok, so update time:

I checked that the oil was not coming from the front main. Then I added UV Dye and let it run for 15 minutes (and inspected while running). All of the uv dye appears to be coming out on the drivers side of the motor with the majority of it appearing in the red circled area (hard to see the uv on my phone pics sorry). I verified that the oil is also not coming from the dip stick tube above the oil pan.

If this was the rear main wouldn't it be coming out of the bottom of the bell-housing and getting everywhere (TC etc)? From what I see either I didn't add enough black RTV to the rear main t junction or it is leaking from the seal between the block and the rear main assembly (one piece on the 5.7)? The 2nd pic shows some more oil pooling at the front of the motor (still drivers side).

RonJon '06 · Sep 11, 2014

If it were the rear main seal I think there would be oil and dye up above and on the TC like you said. On mine there is oil on the gasket all around the pan and it runs towards the rear and drips off. I read last night that a 1.5" strip is supposed to be applied at the four junctions. I'll probably try to redo mine this weekend since it's due for an oil change anyway.

FL2500 · Sep 11, 2014

Yah, can the gasket be re-used since its new? I really hope I get it right this time, disconnecting the oil pickup is a pita (4x4 2500), but better than lifting the motor.

RonJon '06 · Sep 11, 2014

I'm looking at the same thing you are and I'm planning on reusing mine. Before I pulled my motor for the rebuild I unbolted the oil pan to take a look inside and I think there's enough room to clean it up and reseal it without having to lift the motor and remove the pickup. The bolts aren't torqued too much so I don't see why the gasket wouldn't still be good. I hope it works this time cause the estimate to get it fixed at the dealership was $800.

FL2500 · Sep 11, 2014

Going to get another new gasket, some acetone and do this one more time... I have a 4x4 too and I can get the pan off without lifting the motor: unbolt pan, get in there with a 13mm socket and disconnect both oil pick up line bolts and it comes out.

FL2500 · Sep 13, 2014

So the bad news. I checked again with the UV light and got into a position where I could see into the bellhousing better. Rear main is leaking, I did the oil pan anyhow just to make sure and the leak is the same.

So, being as we just put this motor together I know the rear main cannot be changed without separating the motor from the transmission. Easier to pull motor again or pull the trans back? If pulling trans, is it just disconnect both drive shafts, any electrical connectors, TC selector and unbolt and move back? Any tips on that process are appreciated.

crazzywolfie · Sep 13, 2014

is the engine a rebuilt engine or is it used?

i think working on the engine when it is out of the truck is usually a lot easier.

FL2500 · Sep 13, 2014

Rebuilt, new everything (including rear main etc). My guess is defective rear main or not installed properly (folded). Trying to decide if its better to slide the trans back or to pull engine.

crazzywolfie · Sep 13, 2014

since it is rebuilt you should contact the rebuilder and see what they have to say. i don't know how much work it is to pull an engine on a new vehicle but i think it would make it a lot easier to replace the rear main seal with the engine out

Oil leak..but from where?

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