Mazda 6 Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
444 Posts
Discussion Starter #1
Hi

I'm chasing a minor oil leak, not sure if its motor or gear oil (have a cold and cannot smell), and trying to find out why all gears are hard when the transmission is cold.
I washed the bottom of the engine last night, drove today and went to check. There was one drop coming from where the transmission meets the engine, right next to where the flywheel opening is.

I removed the transmission's fill plug and was surprised to hear a "hiss" which indicated that it was pressurized. That would explain the leak (if its gear oil).
It happened once to me on my AWD Sienna where the rear diff was leaking, dealer wanted to change all 3 seals for about $800. I found that the vent was stuck close causing it to build pressure when it got hot. Cleaned the vent and the leak went away.

So, does this transmission have a vent? Where?
 

·
Registered
Joined
·
444 Posts
Discussion Starter #3
Although I'm getting crickets.... I'm going to post my findings /progress hoping it helps others in the future..

Luckily I still had a bunch of pdfs that I downloaded back when I had my 04. I found the Manual Transmission Workshop Manual and found that indeed, this transmission does have a vent.



I'm going to try to get to it tonight. I bet this thing is seized and stuck close.
 

·
Registered
Joined
·
444 Posts
Discussion Starter #4
MTX - Air Bleeder

Ok, continuing with my monologue, here is what I found. I have to say that I'm surprised that no one has had (or identified) this issue before in this forum, or is it maybe that many people are driving around with a similar oil leak and haven't done anything about it...

So after removing the battery and battery tray, I found the vent. It's hidden right under the starter. These vents have a metallic cap that should rotate and move up and down freely. Well, mine was seized as I've suspected, the salt and road grime had done its job on it.
With it seized, as the transmission gets hot, the air inside it also gets hot, the air and oil expand pressurizing the transmission if the vent is permanently closed. This pressure has to release somehow and the weakest points are the oil seals so you get a minor leak.

Luckily it loosen up pretty easy, I was able to turn it with my fingers. This vent seems to be pressed-in (not bolted), I didn't find an easy way to remove it so I decided to clean it in place. A few rigorous spins, degreaser, hot water and lube did the job.





I re-washed the bottom of the transmission, I'll check again in a week or so. Hopefully this is it.
 

·
Registered
Joined
·
1,826 Posts
Thanks for the follow through on your problem. I just bought my gen 1 a year ago and plan to drive it a long time. There aren't many of us left here, but those who are appreciate the info!
 

·
Registered
Joined
·
941 Posts
I will now be very closely examining this when I replace my started in a few weeks, the info is greatly appreciated!
 

·
Registered
Joined
·
444 Posts
Discussion Starter #8 (Edited)
Update.

After loosening the vent's cap, the oil drip persisted. I was planning to change the trans oil so I decided to wait till then to look at it again.
Ordered the Redline MT-90 as widely suggested in this forum, had to cross the border and go to Michigan as I could not find it in Ontario.

Opened the fill plug first and guess what.... heard the "hiss" again.... the transmission was again under pressure. Completed my oil change and then decided to remove the battery and tray and see if I could remove the vent and clean it thoroughly.

Didn't know if it was press fitted or threaded. Space is tight so I took a very small vice grip, grabbed it by the base and started turning it counterclockwise. I was glad to see it turning. After numerous turns it came out, the thing is press fitted.




(see how much cleaner my transmission is now :wink2: hate having a dirty engine)

Once off, I tried to blow air through it, it was completely plugged (or seized). I placed it in hot water & soap for a while and then tried to clean it with a toothpick. There was a rubbery/springy thing inside it which made me think and later confirmed this vent is more of a one way pressure relief valve than a vent. This is new to me, the one I found on my Sienna's rear differential was just a fitting with a lose cap on it.
Once cleaned and unplugged, I started throwing WD-40 at it. Got air to go through it with a bit of effort so again, it behaves like a pressure relief valve.



Putting it back required some imagination, is pressure fitted and the starter is on top of it. Used a bar and applied pressure leveling against the starter, then I gently tapped it down using a hammer and screwdriver on the edge of the base.

I'm not 100% satisfied with this as I do not know if the valve is opening at the pressure it is supposed to and I do not know if the cleaning process and years of grime might have altered this. On my next opportunity I'll stop by the dealer and order a new one, so far I haven't been able to find the PN but it cannot be that expensive.

Here are my thoughts about this:
- If you have an oil leak coming from one of the seals, replace this valve. Its a quick DIY that might solve the issue.
- I wouldn't waste time cleaning it, as I said, you'll never know if its working as intended.
 

·
Registered
Joined
·
44 Posts
Thanks for this post. Did the reverse switch on my 04 over the weekend. When I pulled it got a big whoosh of pressurized air. I'll be digging into this vent right away.
 

·
Registered
Joined
·
44 Posts
Well between that last post and this weekend the vent plug actually blew out of my transmission. Went to clean it and it was gone, Just a hole in the trans now. I'll need to figure out a different vent since this part is NLA.
 

·
Rally Racer
Joined
·
1,881 Posts
1 - 14 of 14 Posts
Top