Here we go again.

Usual truck, 2000 F250, 4R100 transmission, 2WD. 173kmi now.

I have been fighting with the trans fluid level since when I had the hose failure last year as related in another thread.

This is the sequence of events: hose fails, ATF goes all over the place, I park the truck, find the issue and fix it. No more leaking. I add in 6 qts of ATF to start, on the assumption that it would be pretty difficult for the engine to pump out a lot more fluid.

I start the engine... nothing on the dipstick. Bone dry. No problemo. Add the rest of the second gallon -> total of 8 qts added.

Run the truck five minutes going through the gears, measure it again... OOPS the level is ABOVE the whole plastic piece at the end of the dipstick. How is that even POSSIBLE?

No problemo #2: get wrench, open trans pan drain. Get 6qts out (measured). Add a gallon back in. Now we're at -2 qts from before, so at a net of 6 qts added. Here, BTW, is where the '90% new fluid' came from.

Level with trans cold is about 1/4 on the 'C' side of the dipstick, so I call it good (wondering why with the same net before I didn't have anything on the dipstick...).

Take the truck out, it drives fine, drive ~500 miles. No trans issues.

Today, I went to get parts and I figured I'd check the trans level with the truck at operating temperature. Put it in park on a level surface (the same one as the previous times, to within 4", BTW).

I take the trans dipstick out... bone dry again.

That is not possible unless some fluid is coming out of the trans... so I go under the truck with a mirror and a flashlight. Just like when I fixed the leak, there is not a HINT of any fluid under the truck. Nothing at all.

Can someone explain what is going on please? I am at a complete loss. All checks were done with the engine at idle and the truck in the same spot. Temperatures have been between 80F and 50F but that should not make that much difference (in particular, the level at operating temperature should be HIGHER than the cold one no matter whether the 'cold' is 80 or 50F...).

There are no traces of anything (oil or other) under the truck or on the truck anywhere. Once I fixed the leaks I degreased the whole thing so that I'd be able to detect any new leaks. The truck is still clean.

 

The only guess that I have is that there was fluid in the dipstick tube that gave a false high reading earlier.

 

Thank you Mark. That's what I figured, but in order to avoid that I did take the level multiple times, back then, and I was careful to note where all the little honeycombs were filled.
I will try adding a quart, going for a brief drive (which will also give the fluid in the tube time to go down and make false readings less likely, I'd think) and measuring again. I am assuming that the range on the dipstick is greater than a single quart, but I will report back.

 

Following up on this, since today I took the truck out again. Without adding any oil I drove ~55 miles. At the end of the drive, with the truck level in the usual spot and in P, the fluid level covered the LOWEST row of hexagons in the C range of the dipstick.

So I added 2 qts of ATF, ran the engine another five minutes and the level got to the 'H' in the H range of the dipstick - so about 45-50% of that range. Since the oil I added was around 70F, I would expect the level to rise a very small amount more when the entirety of the fluid goes back to 170-175F. I shall report back in a couple of weeks.

 

I realise I never reported back on this: trans oil still happily just above the letter on the hot side of the dipstick. No leaks or seeps. Transmission is... mostly OK, even after (very) prolonged sitting. I'll call this a win.