Rear main leak? Not so sure.

[Gregs672000]

Greetings all. While the head is off I pulled the engine to address what I thought was a rear main leak. Now that I get a close look I'm not so sure it's leaking vs leaking from the oil pan gasket. What do you all think? I took a couple of pics. It's kinda hard to tell in the pics but I noticed that there's very little oil visible behind the crank (looking through the bolt holes for example). I see more of an issue with oil seeping past the oil pan gasket. In the pic of the backing plate, note that the center of the plate (which would be directly under the seal) is generally dry in the middle vs either side (the side you're seeing would be facing forward, so wet/shiney areas are reversed, but you can see what I mean). There's also a pool of oil in the recesses of the block where an oil pan bolt(s) comes through on either side of the crank. I've never had a rear main leak. What ever the source, it leaks a fair amount and I can't have it! I don't want to disassemble or disturbe the bottom end needlessly, but the quandary is do I risk it not being the main, seal up the oil pan better, and go forward only to find I have to pull it again because there's still a leak? It's not the other typical oil sources like the tach cable, though there is likely some coming from the cam cover... no way it's all that drip from there though. I notice these engines develop a lot of internal pressure and I wonder if this is forcing the oil out a weakness in the pan gasket. This is also a new block to me and this pan had not been on this motor before. Thanks!

[unklpat]

Greg, the same thing happened to me. When my motor was out, no trace of oil from the rear main. Back in the car, new trans, new oil pan gasket, and leaks that are driving me nuts. Dave thinks it's the pan gasket, or pan not flat on flanges. I do have a bolt on passenger side of timing cover that weeps oil, possibly due to the amount of oil flinging going on. I've changed pan gasket once, with no change. Pat

[unklpat]

Upon closer inspection, the problem appears to be the aluminum oil pan. I will help you solve it, by trading a steel one at no charge. glad to help you out. Pat

[steve_car]

Upon closer inspection, the problem appears to be the aluminum oil pan. I will help you solve it, by trading a steel one at no charge. glad to help you out. Pat

Good one.

[C.Costine]

My observation of many different oil leaks is that the oozing oil leaves a trail of oil but also a path which is clean of pretty much any other grunge. I don't see that under your crank. Keep in mind also that pretty much any oil leak that leaks out of the motor ANYWHERE is going to run down and towards the rear until it gets to the oil pan gasket and then follow that to the rear.

[richard]

Did you clean the exhaust ports after you removed the head?

[itsa68]

The rear main seal area of the oil pan always seem to be a pain leak area. I've found that if the side seal ends are proud, they can slightly deflect the pan gasket locally and create a small leak path. Also if the side seal is below surface flush and the pan has been previously defected from over-tightening against ends of side seals, it will create a small leak path.
I finally got rid of the leaks created in this area by utilizing a small amount of red permatex high temperature rtv gasket maker in the local area around the ends of the side seals,( fill in seal high/low) , tapering to a thin film towards the nearest block pan bolt holes. The rtv was left to partial cure before final tightening pan down. (I also used spray gasket dressing on the pan gasket surfaces to also ensure gasket seal).
That area is now dry as a bone and no more drips on the garage floor.

Hope that helps.

Cheers
Ray B.

oil_leak area.jpg

[C.Costine]

The RTV for the side seals is in the instructions for all of the various rear main seals of this type that I have done or seen.

[Gregs672000]

Did you clean the exhaust ports after you removed the head?

Some... sprayed various cleaners in the ports checking for leaks, spent some time cleaning carbon out anywhere near the valve but not worrying about getting the whole port totally clean and shiney. I'll probably do more as I go though and clean and lap the valves. I'm expecting less build up in the future with better fuel control.

Thanks for the leak info posts Ray, exactly what I'm looking for. I probably dressed the gasket very lightly with some rtv but not the side rubber seals... thanks for the detail.

[sunbeam590]

Also the oil passage RH back of head side, ,and also dissy Tacho seal, minor leaks here will also end up under main rear seal.
But just worth mentioning.. Good luck..

[Gregs672000]

I'm not really sure what to think here... I really thought I'd find evidence the pan gasket was leaking but I didn't find any spots where it looked like oil got past. Maybe near one of the bolts. The tach area was fixed earlier and not the source. Had some leaks from the block-off plate for the fuel pump that likely traveled, but I'm not convinced it was only that. The head gasket oil area looks like it was sealed fine, but I do see signs of oil running down the back of the block, so maybe the cam cover gasket added in. At his point im very reluectant to redo the rope seal with no clear evidence of leaking. Hope I don't regret that decision.
Thanks for the observations!

[redroadster]

Oil dye and the yellow glasses and uv lite

You have detonation going on in the engine, which creates high pressure, bet it's going to be a reacurring problemo
Note all manufs post 81? have a double recessed channel in the alloy mating surfaces for the RTV to grab hold of
Nissan used /had oil sealing RTV that was the consistency of body putty 2 or 3 x tougher than reg silicone but ( $$ and it separated in the tube super funny and super thick )

[Gregs672000]

I'm reducing compression to a more street friendly level and will be using the Toyota sealant going forward. I just don't see the rear main leaking, and with the motor apart I can't clean it and run it to find the true source. I'm just hopeful that I'm right about the main seal and don't have to deal with it leaking once it's back in the car.