View Full Version : Replacing main oil seal, what else at the same time?
Wheaties
I tried to get an oil change and was told that my main seal was leaking quite badly. The is lots of oil crud around the seal at the bottom of the engine and I have noticed that I'm putting more oil in than should be necessary.
So, I'm reading here that the easiest way to replace the seal involves pulling the engine (correct me if that's wrong) and I'm wondering what else I should do if that is the case.
1995 base, 128,000 miles. I've owned it since 60,000 miles and have done relatively little work as it was previously owned by a mechanic who took care of everything before I bought it.
Thoughts?
shuiend
There are 2 seals at the bottom front of the engine that could be leaking. You have the crankshaft seal which is on the oil pump. You generally change it when you do the timing belt and water pump. This is generally the seal that leaks. At 128k you are due for your second timing belt change if it has not already been done. I would highly recommend getting an OEM front crankshaft seal from Rosenthal. I have seen felpro and other cheaper seals leaks shortly after install. So the few extra dollars for OEM is worth it.
The other seal is a half moon on the oil pan. This one does not generally leak, but if it does you have to pull the pan to redo it. There is a half-moon on the front and back. People say you can drop the front subframe and do the oil pan seals that way. I personally think pulling the motor and working on engine on a stand is the much easier way to do it.
Joe824
If the leak is bothering you enough to do something about it, do a full timing belt/water pump job, as all that has to mostly come off to replace the front crankshaft seal anyway.
Shuiend is right, that's likely what it is vs the half moon or oil pan sealant. However, I'm one of the few that actually did have a leaky oil pan gasket AND half moon seal leaking at 85k miles. I removed the engine to do that work.
Engine removal is definitely not necessary for the timing belt work, but any job is easier with the engine at eye level on a stand ;-)
jspadaro
He only said main seal, which i assume would mean rear main seal?
Before doing anything, I would clean the motor up and get under it with the engine running to see where the leak is coming from. You want to be sure it's the RMS before you take on the job. It could be something easier, like the valve cover, cam angle sensor, or even the front crank seal.
Another approach is to use UV dye, add it to the engine oil with the car on stands, and get under it with a UV light to find leaks:
http://did-it-myself.com/finding-oil-leaks-with-uv-light/
If it's actually the front crank seal, it's a pretty straightforward operation to do with the engine in the car - all you have to remove is both belts, the intake, and the valve cover, and you should then probably go ahead and do a timing belt and water pump job as the others have suggested:
http://did-it-myself.com/miata-motor-timing-belt-water-pump-seals/
If it's the rear main, though, then yeah, it'll be a lot more work. In that case, you can either remove the engine and transmission together or drop the transmission by itself. I would probably try to drop the transmission by itself. Either way, be aware this is a lot of work - you may want to shop it out. If you drop the trans by itself, harbor freight / northern tool sell a cheap transmission jack that can make it easier. The trans isn't that heavy - the worst part of the job is getting to all the bolts holding it in, and breaking them loose if they've never been out before. A close second to worst part is realigning the transmission onto the input shaft during reinstallation.
If you choose to remove the engine and transmission, I have a detailed writeup for it:
http://did-it-myself.com/removing-a-miata-engine/
Either way, I have a writeup on when I did my rear main:
http://did-it-myself.com/miata-clutch-transmission-and-rear-crank-seals/
When doing a rear main seal, the other things to consider doing are a clutch job (you can get an OEM-type Exedy for about $100 that includes a new pilot bearing and release bearing) and if you track the car or any performance driving, you could consider a coolant reroute. For street driving, that's probably unnecessary.
Hope that helps.
shuiend
He only said main seal, which i assume would mean rear ma
I did not even think of the rear main seal. I thought I read in the original post something about the front of the engine, looking back at it I was wrong. Very possibly could be the rear main seal.
Wheaties
I was thinking of the front seal when I posted originally. But now I will investigate further to confirm.
Thanks for the advice everyone. Either way it looks like I'll have something extra to do.
jspadaro
Ah, fair enough. If it is the front crank, you can definitely do that with the motor in the car, but look at getting your timing belt, water pump, and cam seals out the way when you do it.
If the leak is coming from the front, it's probably one of those 3 seals or the valve cover anyway. The half moon on the oil pan is possible but less common. At 60,000 miles with no major maintenance, you're getting close to wanting a timing belt regardless.
The timing belt is the most annoying part to deal with, and it has to come off for the front crank anyway.
forrer13
And if you do the timing belt and water pump go ahead and replace the cooling system hoses for good measure as you have to drain the cooling system anyway. You may even have to cut the radiator hoses to get them off and at 128,000 miles they are due to be replaced before one begins to leak.
How do you HLA's sound? If you do the timing belt now is the time to pull them and clean them thoroughly too.
jimbonnie
Leakage from the cam position sensor can find it's way to the bottom rear of the engine and may mimic a rear main seal leak. Make sure that's not the problem before even considering pulling the engine or transmission.
MC70
Ah, fair enough. If it is the front crank, you can definitely do that with the motor in the car, but look at getting your timing belt, water pump, and cam seals out the way when you do it.
If the leak is coming from the front, it's probably one of those 3 seals or the valve cover anyway. The half moon on the oil pan is possible but less common. At 60,000 miles with no major maintenance, you're getting close to wanting a timing belt regardless.
The timing belt is the most annoying part to deal with, and it has to come off for the front crank anyway.
CAS O-ring, radiator hoses, thermostat, and injector seals as well. It's an expensive (for a Miata) bit of work with parts in the $350 range, however that'll probably get you another 100k or decade down the road.
jkspeed
If you're doing the front/rear main, do everything you can while the motor is out.
basically everything here, except maybe not valve seals, head gasket, bearings, or PCV (if yours is ok). This kit isn't for a 95, but you get the idea of what you need. I sourced all the parts separately on my 94. PM me if you want my spreadsheet. basically all the legwork to order what you need on a motor "refresh."
https://www.flyinmiata.com/fm-engine-rebuild-kit-90-91.html
Wheaties
Thanks for all the input everyone.
It ended up being the rear main seal and I decided to dive in with the whole refresh.
Timing belt, water pump, CAS seal, both oil seals, cleaned HLA, rear seal, and many more.
A week of evenings later and my 95 is running better than I remember.
Special thanks to jkspeed for the list of parts for an idea of what I needed.
And since Miatas are never complete I lost a headlight on my first drive and have ordered Cities to replace. So fun. :thumbs:
Schroedinger
Leakage from the cam position sensor can find it's way to the bottom rear of the engine and may mimic a rear main seal leak. Make sure that's not the problem before even considering pulling the engine or transmission.
I was going to post the same thing. I had oil leaking all down the back of my engine, turns out it was from the CAS o-ring. I changed it yesterday, pretty simple fix. I'd start there, and pull the valve cover and replace that gasket too. Having the valve cover off makes it much easier to get the CAS aligned.
Dennis Nicholls
It ended up being the rear main seal and I decided to dive in with the whole refresh.
Timing belt, water pump, CAS seal, both oil seals, cleaned HLA, rear seal, and many more.
I'm confused. Normally a rear main seal job involves pulling the tranny and doing a clutch job too.
vBulletin® v3.8.10, Copyright ©2000-2023, vBulletin Solutions, Inc.
For more information front crankshaft oil seal, please get in touch with us!