Transmission oil change - temperature
 

Hello all,

So I have been planning the Auto Trans oil change for some time and yesterday morning I plugged my friend's VCDS to make sure I could read the ATF temperature and yes I was able: 40° Celsius with the car off after sitting overnight.
The weather is already hot in Middle East but being the outside temp at around 36° C I was expecting something lower to start with but apparently the parking lot keeps the heat, and this brings the issue of having to fill up until the fluid reaches 40°C: I was thinking of filling up while running the engine until it drips with whatever temperature reaches, install the fill plug, stop the engine and let i cool down to 40°C to then start it again, switch gears and open the fill plug and let it drain until it dribbles only. Is this a good idea or will it harm the transmission? I can always stop adding at 8 qts and check again after cooling down to 40°C.
On the other hand would it be better to wait until lower temps come and do the change strictly as in the manual?

thanks

I just went through this.
Fill it up as much as you cold.
Start it up and cycle through the gears 4-5 times.
Shut it off quickly.
Fill as much as you can.
Check the temp. I fill up to 115f and it doesn't seem to make a difference. The fluid doesn't stay @ 104f very long.
Do a final fill, goaling for the 104f, and filling until you get a nice little stream out of the fill hole. Make sure you have the filler tube deep into the pan and whats running out of the fill hole isn't coming from the tube you are pumping fluid in thru.
Reset the adaptations.

I think you are missing his main point.

He's in a very hot environment.

His "cold" trans temp is already up to 40C.
Interesting problem.

Personally, the idea of filling it as full as it will go, regardless of temp, then letting it 'cool down to 40C' and checking the level would be fine.
I also agree with J that a few degrees hotter wouldn't make much difference.
I don't think the small difference in volume due to heat expansion won't do any damage.

Thanks for your inputs.

I think J'sWorld's procedure might work as well and seems to limit the amount of overfilling in each fill instance, if that makes sense, however I understood from reviewing other threads and DIY that as soon as you stop the engine the trans oil goes back to the pan and would drain when opening the filling plug whereas from the procedure seems that the trans would hold the fluid. Maybe I'm missing something or did not understand correctly how the trans behaves during the process.

It is also worth considering that I wanted to gravity-fill it and this would take time. I don't mind spending a lot of time on filling and cooling cycles since I have two days to get it done but I want to make sure I don't damage anything. In this way J'sWorld's procedure seems to keep the atf temp 'controlled' vs filling at once but I could as well carry on with my proposal in several steps.

I guess the key is to keep the temperature controlled and not letting it go high, but what becomes too high? No clue.

Well, if I understand it correctly, having it at the correct temp insures that it's filled correctly.
Since fluid expands as it gets hotter, having it too hot (expanded) would result in under filling. Having it too cold (not your problem) would result in over filling.

Perhaps if you park somewhere other than a black top parking lot, it wouldn't be quite as hot when it was 'cold'.

From what I've read on here (and my single personal experience), filling it to 'cold full', then starting it up and moving the gear selector into "D" & "R" a couple times, then checking temp gets you to proper temp (when the room temp is ~70F - 20C) in a few minutes.
I'd think that if you 'cold' filled it, started it up and moved the selector back & forth a couple times, then topped it off you'd be pretty close. It really doesn't heat up all that fast if you aren't putting much power to it.

Correct level is measured with the motor running in every auto trans I've ever known of.

Nope. Didn't miss anything. It's also very hot in Texas. He doesn't have a problem. What do you think the tech's do in places like Palm Desert, Las Vegas, or Pheonix? They let it cool to ambient (110f-125f) because a customer is not going to want to wait 2-3 days for a trans fluid change.

Thanks again for your replies.

That makes sense and adds a reason to make sure all the required oil goes in. I definitely don't want to run the trans under filled.
Parking the car somewhere else means out in the street where I am not allowed to do any work so I guess that's not an option. I'll do the job on Wednesday and the forecast temps will lower plus I'll be starting before sunrise to catch the 'cooler' time of the day.

So no trans fluid oil goes back to the pan after every fill + gear switch + engine stop cycle? I am sure I will need many cycles doing a gravity filling.

In any case is good to know how to approach the oil change and having options for these temperature conditions. I think I will adapt the procedure as I go.

Key note: The fill plug is always removed and installed with the engine running. I.E., start, remove, fill, install, stop. I think the gravity fill situation is going to be a bad idea. Go get yourself a $5 hand pump and some clear vinyl/pvc tubing if you have to. I have done it that way with the kind that screws onto a quart bottle. I just did mine with my motive pressure bleeder. I had bought a drill pump but it turned out to be a pos. From what I have observed it wont stay @ 104f(40c) long enough. Just keep filling till about 115f. It will be fine.

Here's the idea:
Your cooler circuit wasn't drained so that part of the procedure can be skipped. Try to catch your extra fluid that drains out into something clean so it can be used.
Fill it up cold for the initial volume, engine off, so you have something in teh pan to work with and fill the valve body with on the next start/fill.
Start it up and then remove the drain plug. Fill until it runs out. Cycle the trans thru all the gears several times pausing in each gear. You will be out of time for temp. Screw in the plug hand tight and shut it off.
Cool down.
Start it up and remove the plug. Top off @ 40c(104f). A SMALL stream running out is ok. You should be good to go @ this point. You can always cool down and double check again.

Got it, that is a very clear explanation.

I would have bought the hand pump long ago if it was available at any shop I have visited - many by now - but somehow couldn't find one. I'll give it a try later today on a couple more shops and if not I'll order online. Pumping the fluid in fast seems to be the key in this case.

Thanks for your help and time

Edit:

If I can fit the hose instead of the nozzle, this will be my only hand pump way forward I am afraid;

https://cimg2.ibsrv.net/gimg/rennlis...617be51826.jpg

Kadn33 - I used one of these - it worked really well.:
I just removed the end fitting and put some flexible tube onto the end of the straight pipe.
You can fix the flexible tube to a bent coat hanger or wire to get the hook shape to pump the fluid down into the transmission so it doesn't flow straight back out the fill hole.
The handle has an on/off valve that makes stopping and starting the flow very easy.

https://cimg6.ibsrv.net/gimg/rennlis...1b09bb21cd.jpg

Great info Joefus, good to know it works with a gardening pump. The one you show seems more robust and having the valve is a plus, I hope I can find one like that.
And yes I thought as well about the bent coat hanger as the way to keep the fluid going in and the hose in place but is good to have it written here anyway for someone else's future reference.

Thanks a lot for your input.

On the cheaper side, this worked really well for diff oil and was cheap- just be prepared to make the jokes when you get an Alexa notification that your "slippery pete fluid pump" was delivered

I bought these for my diff and Tcase fluid change. I couldnt imagine pumping 8 quarts into a trans with it though. :)

Very true, but we are going cheap and not convenient or efficient :D

in that case....

https://cimg6.ibsrv.net/gimg/rennlis...bc3559358a.gif