Transmission oil: How full is too full?

[Meanwhile]

My truck has a 10 speed automatic in it and there's a small spin on oil filter on the back. I've changed this filter 3-4 times now and when I check the oil level there's always oil at the fill plug running out. I didn't think much of it because my driveway isn't close to being level. The other day I noticed a puddle of oil under the truck, about pie tin size under the transmission. I took the truck to a small repair shop down the street from where I was and it turned out to be one of the lines for the cooler was leaking. They made up a new line, put it on, checked the level and the guy said it was full. I guess I'm having trouble understanding how it could still be full. Talking to the shop owner, I remembered reading that someone here had a problem with the trans cooler leaking antifreeze into the transmission. I asked if the this may be whats going on with mine and was told no, that mine doesn't have any coolant lines running to it. How over-full is too full and can it do any damage being over-full?

Maybe I got lucky and caught this early into the leak?

[smorgan87]

They hold around 4 gallons of gear oil and always fill until oil dribbles out the fill hole so usually theres a little extra anyway. A small drip would take a very long time to lower the level on one. For example i destroyed the rear bearing on a 13 and had oil dribbling out the back, when i finally got around to rebuilding it there was still probably 3 gallons or more left in it. Theres 2 types of coolers on them, Liquid/liquid and liquid/air. The liquid/liquid does more to heat the tranny than cool it and ruins things when they fail. Liquid/air actually cools the oil and if it fails u know it by watching oil flow onto the ground. Its also worth noting that the level would have to be quite low before it stops lubricating.

[Meanwhile]

Thank you, that’s good to know. Today I decided to clean up some oil and make sure there’s nothing leaking. I’m pretty sure this trans cooler has coolant running to it, since it has blue silicone hose on the one side. I pulled the plug on the transmission to check the oil level and it didn’t run out. I can touch it with my finger easily. I’m guessing I’ll be ok to run it a couple days until I can find some more oil?

[Coronado126]

(11-26-2020 )Meanwhile Wrote:  Thank you, that’s good to know. Today I decided to clean up some oil and make sure there’s nothing leaking. I’m pretty sure this trans cooler has coolant running to it, since it has blue silicone hose on the one side. I pulled the plug on the transmission to check the oil level and it didn’t run out. I can touch it with my finger easily. I’m guessing I’ll be ok to run it a couple days until I can find some more oil?

It's more than likely perfectly fine.

I can't find the drawing I used to have, but stick your finger straight in just past the 2nd knuckle, and bend your finger down roughly ~1". If you can touch fluid you are good. Anymore than that and you need to top off until it is level with the fill plug hole.

The above applies to autoshift (not real automatics!!) and manual transmissions, and differentials on semi's.

[Meanwhile]

Thank you.

[smorgan87]

liquid/liquid exchangers will have 4 lines to em. 2 coolant and 2 oil. The ones ives seen were bolted to.the top of the tranny and looked like a pipe with 4 threaded bungs in it. (If you have one of these i strongly suggest swapping to a liquid/air exchanger.) As stated above, if u cant feel oil in the plug u need to top it off asap.

[Meanwhile]

Thanks! I’m pretty sure the oil level is safe, it sat parked for over 12 hours before I checked it. I put my little finger in a bit past 1st knuckle and it had a lot of oil on it. I kinda freaked out I guess when I found that leak thinking the worst and forgetting how far a teaspoon of oil can spread of time.

I had wondered about liquid VS air coolers and if an air cooler would be better. I have noticed that this truck shifts better in cool weather than when it’s hot out.

This isn’t a very good picture but I’ll post to show what I have.