Mystery oil leak
 

My track-mostly MSM was due for a timing belt so I bought the full kit from FM, plus a water pump locally (making sure that it had a cast rather than folded steel impeller). Two weeks ago I took over part of my brother's garage mahal and did the work. I received FM's tool kit as a Black Friday bonus, so I had everything required in order to change the main crank and front cam seals. After everything was buttoned up, I backed the car out of the garage, jacked it up in order to properly burp the cooling system and, to my chagrin, noticed this:

https://cimg3.ibsrv.net/gimg/www.mia...1e390afe9c.jpg

It appeared as the car was warming up and was fairly copious. My first thought was that I'd screwed up the installation of the main crank seal, probably because I didn't have a proper seal puller and ended up removing the rather crusty original seal with a screwdriver and potentially scoring the crank nose. In preparation for doing the job for a second time, I purchased the and made plans to return this last weekend. After I pulled the main pulley off, this is what I noticed:

https://cimg8.ibsrv.net/gimg/www.mia...b00781b011.jpg
https://cimg2.ibsrv.net/gimg/www.mia...0714071a9b.jpg

As you can see, the area around the seal itself was pretty clean and there was no trail from that area to the dark puddle that was apparent in the gap between the block and oil pan. In fact, there was a lot of residue that had to be cleaned out. Anyway, the old/new seal came out easily with the proper tool and didn't appear to be torn. I checked the surface of the crank nose and thought that there *might* be a little ridge and it was removed using 800 and then 1200 grit Scotchbrite pads. The new seal went in as designed (the FM tool sets the depth perfectly), I buttoned everything up again, backed the car out of the garage, jacked the front end up and started the engine. As it warmed up, I saw exactly the same type of leak in exactly the same place (I took this picture after wiping the pan, so it doesn't look as it leaks as much as before, but it pretty much does):

https://cimg9.ibsrv.net/gimg/www.mia...802aadb876.jpg

So, what gives? It's not the camshaft seals, as they were replaced and disassembly showed no leaks in that area). I'm fairly certain that it's not the main crank seal, as that area is clean and, despite being a bit of a mechanical idiot, I don't think that even I could screw it up twice in a row. Signs point to the oil pan gasket but the quantity of oil coming out seems far in excess of what could leak from that area, particularly when the nose of the car is 30% in the air. Also, why would it start leaking all of a sudden? I could change the pan gasket but the procedure is a royal PITA (either pull the engine or drop the subframe) and I want to make sure that I'm not overlooking something else that might be the cause. Possible that the oil pump is leaking (there looks like a trail of oil on the driver's side that feeds the valley between the block and oil pan). Anybody have any ideas?

Thanks all.

Looks like front "half moon seal" to my admittedly untrained eye

It can only be the pan seal.

If you are having trouble finding an oil leak, a little bit of dye and a uv flashlight works wonders. I had a leaky camshaft seal and this helped me identify it.

:likecat: given

I too saw the trail on the Drivers side trickling down; I'd try to see where that is coming from. More times than I can count, some leak like this had me re-doing something that was fine, because the leak was elsewhere, and I was too focused on the spot I thought it had to be coming from.

If so, where'd these oil leaks come from?
https://cimg8.ibsrv.net/gimg/www.mia...38910f6b0d.png

With more reflection, I really cannot see how it could be the oil pan seal. The nose of the car was 30 degrees in the air and the oil was still dribbling out in a fairly steady stream, indicating a leak under some pressure. I'm inclined to think that it's the oil pump that is leaking, which jibes with the leak circled in the picture above. Not that fixing that is any easier than R&Ring the oil pan - still essentially an engine-out procedure. The question is, if I have to take out the oil pump, do I pre-emptively replace it with a Boundary Engineering billet-geared pump? It's a track car but I'm only running 10 psi boost.

Hmmm... they are above the parting line so they can only have drained there. Potential leak points in the front of the motor I can recall of, are cam seals, oil pump mating surface with the block, crank seal, oil pan half moon gasket. I would expect cam seals making a mess of the whole engine front (judging from mine) though.

Cam seals were replaced and visually confirmed to be free of leaks. I'm fairly certain that the main crank seal is installed correctly and is leak-free. If it was the oil pan gasket, I would expect oil to drip and not stream out (and not at all if the car's nose is in the air). I guess that leaves the oil pump as the likely culprit.

Deer Hunter, I firmly believe (from experience) that if the engine did not leak oil prior to being worked on, and then leaks oil after being worked on, the work caused the leak. If the pan and oil pump were not leaking prior to the oil seal installation, they are not magically leaking now. As difficult as it may be to accept, I would go back in assuming the front crank oil seal is leaking. I agree with you that the leak is only under pressure. I recommend carefully checking the cam seals (if they were replaced) as well. In simple terms, something you touched caused the oil leak. Retrace your steps.

Fair enough, Ken. The plan is to undress the front of the engine (remove all dust covers), reattach the main pulley and then run the engine and (hopefully) see the leak propagating in real time. I'll let everyone know what I find. Thanks again for all who weighed in.

Just get some dye and run the car again. That way you'll know for sure.

Well, it seems that Ken nailed it. My car was towed to a shop I trust and they gave it a look-see. The problem was a poorly-installed cam seal, so the damage was decidedly self-inflicted. Seals have been replaced and everything is now tickety-boo. Thanks everyone.

I'm glad my experience helped you out Deer Hunter. I've done this several times when replacing all the seals on the front of an engine during an timing belt job. I'm careful, lube everything up, use the proper installation tool and something still goes pear-shaped every once in a while.

Glad to hear I am not the only one with this trouble. I have a cam or main seal leaking at something like 1qt/500mi right now. Really need to get some time to get back in there and fix it... Need to order some UV dye.

Worth a read...

https://www.miataturbo.net/engine-pe...m-seals-96499/

I was tidying up the garage and emptied the box o' stuff that came back from the mechanic. Found the offending seal:

https://cimg0.ibsrv.net/gimg/www.mia...801ee0c908.jpg
https://cimg1.ibsrv.net/gimg/www.mia...64ab0bb72a.jpg


I really did a number on it - no wonder it leaked.

To be fair, how do you know the shop's mechanic didn't do some of that on removal? ;)

Possible, I suppose. However, the second seal (which they replaced as well) was completely intact. I'm willing to bet it was all me.