Strange (to me) auto trans fluid level

[russelljones48]

I checked my trans fluid a few days ago - the car hasn't been run in a while - probably 2-3 weeks.  The AT fluid was well above the full mark.  Generally for AT's and specifically in the manual for this car the trans level cold should be below the full mark and rise to the full mark when at operating temps..

So, I took about 1.5 quarts out of it the other day and test drove it today..  wanted to see how it shifted (the shifts have been a hard since I've owned it).  Well it would hardly shift until I got it up to operating temps and then it still slipped at high rpm shifts.  Got it back and the fluid is quite low on the dipstick..  I'm confused...  I don't think it should matter but I'm using Redline ATF (full synthetic) which is compatible with Dexron II and III. 

It's been refilled to just below the full mark at operating temps (per this forum) but I didn't get a chance to test drive it afterwards.  I am assuming that it will revert to previous operations.  However, I've never seen a transmission that reads over full cold and "normal" at operating temps.  Anyone seen this or have an explanation?  Does the torque converter/fluid coupling drain back into the pan over time?

[ja17]

Make sure the car is on level ground with engine running. Moving the shifter through the gears first will make sure the fluid has not drained from the converter (normally it will not). Check level when the engine is warmed. The distance between the marks is about one pint. If you accidentally over-fill, it is easiest to loosen the transmission hose at the radiator and bleed-off some fluid there.

[russelljones48]

thanks.  the car was in my garage on a concrete floor - so level.  It had been driven for about 20 minutes and it was idling when I refilled the fluid so I think it's now properly filled.  I have a suction pump to remove fluid but thanks for the tip on the cooler line.   If the dipstick reads over full again I will try doing what you suggest - warm it up and move it through the gears to see if that changes the reading..  Is typical or for the torque converter to drain like that (if that's what's happening) or is it an indication of some other problem?  My shifts are harsh but I haven't gone through the linkage settings yet or any other adjustments on the transmission.

rj

[Aaron h]

There is a check ball/valve that can weaken with age and cause the fluid in the fluid coupling to leak back into the transmission.  How much it leak over "X" amount of time varies.  This is most notable after the car has sat for a while.  You'll go to start it, put it in gear, and very little or nothing will happen for a new minutes, or until the fluid coupling fills back up. 

Be careful about using synthetic fluids in an automatic that's never been gone through.  Synthetic oils will dissolve the friction material on the brake bands and clutch discs all three clutch packs.

[russelljones48]

Thanks for the explanation and the tip on synthetic fluids..  got a recommendation for the "best fluid"?? 

rj

[Aaron h]

Well, any non synthetic Dextron III will work.  Originally, type "A" transmission fluid was used, and I believe Pilot gas stations still sell type A transmission fluid.  However, the Dextron III is a worthy equivalent that won't hurt anything.  I also believe that in later publications Mercedes approved the use of Dextron III in the K4A.025 transmissions. 

[Benz Dr.]

Every old trans I've ever checked was always over full when cold so I just sort of figured that it was normal. Regardless of all that, fluid level should be right to the full line when hot. Even a bit low seems to affect shifting quality.

Trust me. Most of the time you'll find that your transmission is a bit low due to small leaks so it's a good idea to carry some ATF with you.  The add to full line is about 250 ml - not sure exactly but it's less that you would expect. 

[russelljones48]

So, thank you all for the tips and advice.  I think I'll do a fluid/filter change to non-synthetic Dextron III, do the linkage tour and get the adjustments right and then see where I am.  I haven't read the transmission manual yet so I doubt the check valve is external, so that probably won't get addressed until it needs something else. 

The car does need diapers  ;-)  (I actually use Kirkland doggie diapers underneath it), but I'm resigned to minor leaks  and have higher repair priorities..