Transmission Fluid Leaking from Dipstick

[Nm788]

Long-time reader of these forums, they've been super helpful in building 1.5 Skoolies (thank you!). Close to finishing up the second one and ran into a problem that I can't seem to find information on. Hoping the experts on here could help.

Bought the bus 2 months ago, had it checked out and fixed up as needed, nothing major. No transmission issues. Drove it 90 miles home, a couple times locally and had no issues. It's been sitting in my driveway for 2 months as I've fixed it up.

The other day I started it up to move it in the driveway, did so, and then when I put it into neutral and shut it off, a good amount of red fluid came out of the top of the transmission dipstick tube (which was ziptied). I tried again today, letting it run for 15 minutes and then moving it a bit, no issues. Not sure if it's because I waited a bit or because there wasn't enough fluid to come out. Temps were in mid-high 40's both days.

Is this just an issue of not letting it heat up long enough? Or is there something else that might be wrong (e.g. a clogged filter or vent somewhere)? Thanks in advance!

[CHEESE_WAGON]

Clogged vent or overfilled with fluid, my first guess.

Could also be oil or coolant cross-contamination from trans cooler.

[Nm788]

Thanks, CHEESE_WAGON. Assuming it's not overfilled (I haven't added anything in), is there any way to figure out which of the others it may be? Is there an external vent I can check/unclog? Would I see something in the fluid that would indicate cross contamination?

[CHEESE_WAGON]

Most have a vent, you'll have to look for it as different manufacturers put them in different locations. Could try smelling the fluid to see if it smells of other fluids (no guarantee). Better way is to take a sample of the fluid and have it analyzed. Takes some time but not that expensive and will detect even trace amounts. Might as well do the coolant and engine oil while you're at it for peace of mind.

[ol trunt]

I expect the torque converter drained down over the two month period--not uncommon with older automatic transmissions. The result of draining down is similar to having over filled the trans. Run the engine up to operating temp and check the fluid level adding oil as necessary. Then over the next couple of months run the engine a few minutes each week and see if the "problem" seems to be solved.
Jack

[Nm788]

Thanks, ol_trunt! That sounds like it would explain why the problem seemed to go away after running it for a bit. I'll run it a bit today, check trans fluid levels and top it off if needed to replace anything that was lost.

Out of curiosity, what's the mechanical reason that a drained torque converter leads to the trans fluid overflowing? (my expertise is more on the living space side of the skoolie ;) )

[ol trunt]

Once the torque converter has drained down its volume of oil (several to many quarts) the oil level in the transmission proper high enough for it to bathe the spinning gears which will whip air into the oil causing the oil to expand in a froth which vents out the filler tube and the smaller vent opening.

The actual drain down is caused by wear on the sealing surfaces of the torque converter housing, the steel "O" rings and the input shaft. Until and unless this leak down becomes a daily thing the tranny will no doubt continue working for quite a long while.
Jack

[Nm788]

Thanks, CHEESE_WAGON - will have a look around for the vent.

Thanks, ol_trunt, for the explanation - makes sense.