How much transmission oil should exit the fill port?

JimD

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Good morning,

I have had an intermittent leak on the 85X for years. It looks like Redline MTL more than engine oil and is usually on the transmission side of the engine. After the last couple of energetic drives, I have found small puddles under the trans. Now I am trying to recall if the previous occurrences were during this cars autocross days.

Anyway. The car is parked in the garage, not jacked up at all. If I take out the fill plug at the top of the trans, I get trans oil immediately. I tried this a couple years ago and put the plug right back in due to the volume coming out. Today I decided to try again and let it flow a while. So I pulled the fill plug and this is the puddle that formed on the drain pad I had under the car.
IMG_2034.JPG
That is a decent puddle and it would have grown a bit if it didn't put the plug back in.

My question is this: How much fluid should exit the fill port on level ground? My understanding was that you only filled the trans to the point that a little dribble of fluid came out the port. And the test for a "full" trans was to pull the fill plug and and see if you could feel fluid right up to the port. Am I wrong?

If my understanding is indeed correct, I guess the follow up is: How do you get this much extra fluid into the trans?
 
My understanding was that you only filled the trans to the point that a little dribble of fluid came out the port. And the test for a "full" trans was to pull the fill plug and and see if you could feel fluid right up to the port.
That's my understanding as well. Sounds like your's was overfilled. As to how that could have happened, possibly the trans was filled out of the car and not sitting flat. Or filling it in the car with the car not level. It is also possible to pump a little extra in and quickly install the plug, resulting a bit of overfill. But that would not be a lot, especially with a thinner fluid like synthetic (the thicker stuff is slow to "poor" so you had time to plug it before it comes back out). Overfilling is not a benefit, one of our transmission gurus explained the negative effects of overfilling. And it could possibly be a factor in the leak, so I'd let the excess drain out. Then see if any leaks continue, and after a while check the level again. Might just be the easiest trans leak repair ever. :)

By the way, do you see any signs of exactly where the leak was coming from (i.e. which seal or gasket)?
 
Is it possible the car was leaning to the passenger side when filled and got a bit more fluid than if it was level? My understanding is the same as yours as far as the fill up procedure goes.
 
Thanks for the confirmation on the fill procedure and fluid level guys.

Dr Jeff, by the time I notice the puddle on the floor the leaking fluid is pretty much along the lowest point of the case with a couple drips hanging off. It does stop leaking, I removed the pad with the small puddle the other day and replaced it with a clean pad. No drips in 3 days. I haven't been able to figure out the exact location of the leak, but I hosed it down with brake cleaner today and I will try to remember to look for the origin after the next drive.

Perhaps it is so full the fluid is getting to places in the case it normally wouldn't reach under normal driving. I have been flinging it a bit lately. :)
 
Perhaps it is so full the fluid is getting to places in the case it normally wouldn't reach under normal driving.
Hopefully one of our trans experts will add a more intelligent reply than I can. But I believe one potential outcome of overfilling is it can increase the internal pressure? And that might increase the likelihood of leaks. It certainly will cause more internal slinging of the lube everywhere. Either way, it will be interesting to see what you find after another spirited drive. The fact that your leak was intermittent and not severe is encouraging. Nice use of chux by the way, way cheaper than those "pig mats". ;)
 
Nice use of chux by the way, way cheaper than those "pig mats". ;)
I have hundreds of them. I bought in bulk for my mom and have had to find other uses since she passed. It turns out they are excellent for all variety of fluid leaks. :)
 
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Ages ago I was able to get them from the hospital I was working out of. At that time I was also enjoying a speed boat and they were handy to clean up nasty bilge water.
 
Overfilling will often cause leaks. With the car sitting level, if you remove the fill plug, and oil runs out, its over filled. If you've done this multiple times it sounds like it was significantly over filled.

level the car and pull the fill plug and let it drain until it stops. Re-install the fill plug and see if it still leaks. Over filling can cause leaks at the input shaft and reverse idler shaft.

A note; when filling the transmission through the fill plug, if you raise the driver's side of the car (LHD) to fill the transmission, you will UNDER fill it. This is because the fill plug is located well to the right side of the main portion of the case.

If you jack the rear of the car you will likely over fill because the fill plug is at the rear of the transmission.

I fill using a funnel with a hose in the fill plug, leaving the car sitting level on the ground.

Also, your MTL looks dirty. If its more than a couple of years old, change it.
 
Thanks for the confirmation on the fill procedure and fluid level guys.

Dr Jeff, by the time I notice the puddle on the floor the leaking fluid is pretty much along the lowest point of the case with a couple drips hanging off. It does stop leaking, I removed the pad with the small puddle the other day and replaced it with a clean pad. No drips in 3 days. I haven't been able to figure out the exact location of the leak, but I hosed it down with brake cleaner today and I will try to remember to look for the origin after the next drive.

Perhaps it is so full the fluid is getting to places in the case it normally wouldn't reach under normal driving. I have been flinging it a bit lately. :)

Before your next drive you could spray the suspected area down with some areosol foot powder, leaves a white powder on the surfaces that the leak will remove and show you where it was.
 
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