Oil leak - rear main vs flywheel bolts vs...?
 

I’ve searched the forums and I know the likely suspects of what might be causing this leak, but I want to be sure before I make yet another attempt to fix this damn leak.

Here’s the background: When I bought my ’00 Miata last summer, there was a slow oil leak (2-3 drops after parking it) that seemed to be coming from the pinhole in the transmission bell housing. I left it alone until this winter when I dropped the transmission to replace the clutch and flywheel, and I found the inside of the bell housing and back of the engine block covered in oil (somehow the clutch was fine, though). I also noticed the infamous CAS leak – I had thought that since my ’00 didn’t have a CAS at the rear of the engine, I didn’t have to worry about it. I found out, though, that the plate which replaced the CAS from previous models can also leak. So I replaced the circular plate, and I also replaced the rear main seal and front transmission seal while I was in there, just to be safe.

After I put everything back together, I discovered that I still had the same leak – oil (definitely motor oil since I had just replaced the transmission fluid with redline) coming out of the transmission pinhole. Ugh! So a few weeks later I took it apart again and saw that the rear main seal I installed looked a little bit crooked. That must have been the cause of my leak, right? Wrong! After replacing the rear main a second time, painstakingly ensuring that the seal was flush with the rear of the engine block, it turns out that the leak was still there! It couldn’t still be the rear main, could it? Could it be the bracket around the rear main seal that holds it to the engine block/oil pan?

So here I am dropping the transmission a third time (I’m getting pretty fast now), and I’m looking over everything carefully before doing anything. I was almost ready to start cutting out the RTV around the bracket for the rear main seal when I noticed something. The oil seemed to originate from somewhere around the center of the crankshaft (the flywheel bolts?) and drip down. Here’s a picture of the crankshaft and the front part of the flywheel that bolts up to the crankshaft. They both seem to have oil that starts somewhere in the center and then drips down:

https://www.miataturbo.net/attachmen...ine=1334014322

Here's the side of the flywheel that bolts to the crank:
https://www.miataturbo.net/attachmen...ine=1334014322

Am I seeing this correctly? I would think that if a leak were coming from the rear main seal that I wouldn’t see oil concentrated in the center of the crankshaft/flywheel like this, right? Could it be coming from the flywheel bolts? I used blue Loctite on them both times I went in before, but maybe it wasn’t enough, or maybe I should have used a different type of sealant? What I really hope happened is that the initial leak was from the CAS blank plate, and my subsequent leaks were from the flywheel bolts that I didn’t seal properly. I suppose it might be from the rear main seal if I accidentally nicked the crankshaft when removing it, but I was pretty careful. I hope it’s not coming from around the bracket for the rear main seal, or god forbid, the oil pan seal.

Any input would be greatly appreciated, because I’m getting sick of repeatedly dropping this transmission and I want this leak gone! And track season is about to start…

Looking at the 1.8l crank I have, the flywheel bolts are open into the engine.

I would recommend using "Aviation Form-A-Gasket" from permatex, get the non hardning
It should be found at any auto parts store.
Make sure you torque the flywheel bolts back to spec.

If you are going to do an oil change at the same time, then you can use a little brake clean to clean the bolt holes. Since the bolt holes are open, the cleaner will go right into the oil pan.

If you are not going to do an oil change, just blow them out with compressed air.

The manual for my nb stated to use loc-tite on all the flywheel bolts to prevent seeping oil from the crankshaft. It also says to drive in the rear main seal 3mm past flush.

Thanks for the input. The service manual I have (the one commonly floating around the internet) says to have the rear main seal 0-0.5mm past flush, so maybe I'll tap it in ever so slightly past flush. As for the thread sealant, most of the official manuals I have seen recommend blue loctite, but I have seen many descriptions of using other types of sealant successfully. Since I've still got the leak after using blue loctite twice, I'm leaning towards trying something that will focus more on sealing than threadlocking, maybe permatex hi temp thread sealant:

http://www.permatex.com/products/Aut...ad_Sealant.htm

That is just plumbers paste, you can go to Home depot and get the same stuff for 1/3 the price.

I had my tranny off 3 times before finally deciding it was the oil pan seal - but the engine had been rebuilt previous to that, and so the oil pan seal had been replaced.

I actually use that on my flywheel bolts after trying threadlocker and RTV, works great.

This tool should help people with correctly installing the rear main seal. I am planning on using it in a couple of weeks when I do my rear main seal. I have never locktight the flywheel bolts. I will be doing it this time since I now know that it is recommended.

How about the OEM threadlocker/sealant that comes on new flywheel bolts? I'm now thinking about just picking up some new flywheel bolts from the dealer so I know I've got fresh bolts with the threadlocker Mazda uses. In my case, it might be worth 20 bucks to use new parts up to manufacturer's spec to make sure those flywheel bolts do not cause a leak.

Then I can find out it was actually the rear main or oil pan leaking...

Mazda wants about ~$4/bolt for them.

ARP wants about ~$30 for a set of their Miata flywheel bolts IIRC.

If I were going to outlay the cash, I'd spend a couple extra bucks for the ARP gear. But that's just me, YMMV.

Are you sure the oil pan gasket sealant (black) is OEM? Could the pan have been off? My NB (older) used only gray sealant from the factory.

I am dealing with a leak the same area and have mine apart for the first time. I took the rear seal carrier out, and I determined, rightly or wrongly that the leak was coming from the oil pan seal between the carrier and the oil pan.

I'd clean this entire area off with brake cleaner. On mine, after very carefully cleaning things, oil would reappear at parts of the arc between the carrier and oil pan, wicking through, even though the engine was not run. I'd did the clean and inspect procedure three times to be sure. It did not seem to be flowing down from high on the seal interface, but rather coming from between the two parts.

Your oil seal seems like it should be placed in further (like you indicated in the manual about .5mm recessed to the carrier.)

If you take your carrier off, I just posted my experience on miata.net, though I had some typos. Was a real chore. Do not know yet if I was successful with the leak.

I ordered new flywheel bolts just to eliminate the sealant issue, but I mistakenly ordered clutch plate bolts, so am going to put things back together with the old bolts. Not sure what to use - blue or red Loctite thread locker, RTV, etc. The thread sealant looks interest, but not sure it is available around here - I do not recall seeing it.