ATF temperature?

[demarpaint]

Lets say you took a 30 minute highway drive, then turned the engine off and immediately took the temp of the ATF. Would the ATF temp be hotter with the engine on and the ATF flowing through the cooler, or would it be hotter with the engine off since its cooking in the pan and not circulating through the cooler?

I took a drive for 30 minutes tonight, highway drive then about 1 mile of city driving before backing into the garage. I took a reading after shutting off the engine and noticed the ATF temp went from about 190-207*F, [I was wondering if my laser thermometer is screwed up], then it started to cool off. Next time out I'll take a reading with the engine running to satisfy my curiosity, but thought I'd ask here.

I'm pretty sure temps climb fast once the flow to the cooler stops with the engine off, then they drop as the heat dissipates?

As always thanks!

 

[229]

Your experience is logical but you have to turn it off sometime. The biggest benefit to idleing is to cool down turbos after a run to prevent the oil from cokeing in them.

 

[Colt45ws]

This is something I have not tested. Ill have to make note to do so.

 

[cmf]

It would reach a max temperature and take time to cool down from there. There is no heat input into an at rest transmission that's 200 F in am ambient temperature of 100 F. The heat is leaving the system.

If the pan did measure as a lower temperature before turning it off it would only be because that section of the system is at lower temperature. Meanwhile the torque convertor is probably a good 20-30 degrees hotter and when that fluid drains back down into the pan it can raise the temperature reading on your thermometer, but the temperature of the system as a whole has not went up.

I'm not really sure what there is to test here, so maybe I am entirely missing what you are asking.

 

[demarpaint]

Originally Posted By: cmf
It would reach a max temperature and take time to cool down from there. There is no heat input into an at rest transmission that's 200 F in am ambient temperature of 100 F. The heat is leaving the system.

If the pan did measure as a lower temperature before turning it off it would only be because that section of the system is at lower temperature. Meanwhile the torque convertor is probably a good 20-30 degrees hotter and when that fluid drains back down into the pan it can raise the temperature reading on your thermometer, but the temperature of the system as a whole has not went up.

I'm not really sure what there is to test here, so maybe I am entirely missing what you are asking.


Your explaination of the TC draining hotter fluid into the pan might have nailed it. That's probably what I observed? Is 200+ F a minute or two after shut down normal for ATF? I didn't get a reading with it running, but will next time out. I'm just wondering that's all. The oil pan was about 185*F the same 1.5" up from the bottom. I measured the transmission pan at about the same height. I would have thought the oil would have been hotter than the ATF after my drive.

 

[tinmanSC]

Originally Posted By: demarpaint

Your explaination of the TC draining hotter fluid into the pan might have nailed it. That's probably what I observed? Is 200+ F a minute or two after shut down normal for ATF? I didn't get a reading with it running, but will next time out. I'm just wondering that's all. The oil pan was about 185*F the same 1.5" up from the bottom. I measured the transmission pan at about the same height. I would have thought the oil would have been hotter than the ATF after my drive.

Your attention to vehicle maintenance is admirable. Thanks for sharing this.

 

[demarpaint]

Thanks!

Now all I need to know if 207* F is normal after shut down, and then I need to check after the same trip with the engine idling to see if there is much of a difference. You see people saying ATF temp is anywhere fom 160*F-180*F. I'm guessing that is temp with the engine on. It was interesting to see it rise then fall.

Obviously the TC draining is the hotter part of the transmission. If you read ATF temp charts over, 200F is where ATF fluid life is beginning to suffer, and that is a concern of mine.

A bit OT, but I've seen engines come to a boil after they were shut off. I'm guessing once an engine is turned off there is no additional heat generated, but the cooling system stops cooling, and the hottest parts of the engine must dissipate their heat to the cooler parts. This is what causes the boil over in an engine with an issue, or a rise in coolant temp in a normal engine, I guess.

In older engines it is more pronounced.

 

[SteveSRT8]

Latent heat has to go somewhere. If the flow of coolant is stopped then the temp rises in an engine so I'm sure an Auto trans does the same.

I'm curious why your temps are so high though. Even on track days my car rarely gets to 200 degrees ATF temp.

 

[demarpaint]

Originally Posted By: SteveSRT8
Latent heat has to go somewhere. If the flow of coolant is stopped then the temp rises in an engine so I'm sure an Auto trans does the same.

I'm curious why your temps are so high though. Even on track days my car rarely gets to 200 degrees ATF temp.


I was wondering the same thing about those temps. But I haven't checked the temp with the engine running yet. Are you checking the temp with the engine on or off? I think in my case it is going to make a difference, next time out I'll find out for sure. Last time I checked the fluid level was correct, I'll check that again too.

 

[Rhymingmechanic]

Originally Posted By: demarpaint
Originally Posted By: SteveSRT8
Latent heat has to go somewhere. If the flow of coolant is stopped then the temp rises in an engine so I'm sure an Auto trans does the same.

I'm curious why your temps are so high though. Even on track days my car rarely gets to 200 degrees ATF temp.


I was wondering the same thing about those temps. But I haven't checked the temp with the engine running yet. Are you checking the temp with the engine on or off? I think in my case it is going to make a difference, next time out I'll find out for sure. Last time I checked the fluid level was correct, I'll check that again too.


A mechanical coolant temp gauge will clearly show the temperature rising when an engine is shut off. It's logical to assume the same will happen to some extent with the trans, for the reasons stated above.

The important thing to know, however, is the fluid temperature when the vehicle is running.

I'll throw my experience in for comparison, with a 2010 Vibe 1.8 4-speed auto. Late last July, I drove about 90 minutes on the interstate and the Atlanta outer belt, then filled up with gas, then drove a mile or less in a residential area. I left the car idling and immediately checked pan temperatures with an infrared thermometer. The trans started at 196 and went up to 204; the engine oil pan was 220. I don't know if the readings would be any different while driving--there would be more airflow for the cooling system, but the trans would also be making more heat. I once drove a Grand Prix rental that showed trans temp, and it fluctuated between 196 and 208 while driving.

 

[SteveSRT8]

Originally Posted By: demarpaint

I was wondering the same thing about those temps. But I haven't checked the temp with the engine running yet. Are you checking the temp with the engine on or off? I think in my case it is going to make a difference, next time out I'll find out for sure. Last time I checked the fluid level was correct, I'll check that again too.


The temps are provided in my dash display via the obd port while in operation. My car has a very large trans cooler from the factory that does not go through the engine coolant. From my early studies of this car when new it runs hotter in city traffic due to poor airflow at low speeds.

 

[mechtech2]

This could actually go either way, under different conditions.
But running temp is what I'd focus on.

 

[229]

I think your concern should be more focused on adding an auxillary cooler to get those temperatures down. Also Mercon5 if you have not already installed it.

 

[demarpaint]

I'm going to run it today, again and recheck. My buddy Trav brought up a good point about a laser thermometer. I was about 8 feet from the transmission pan when I checked the temp with it, and that leaves a lot to the imagination. I'm going to take temp readings closer. I already have an external transmission cooler installed. Thanks for the replies.

I'm also going to take a reading with the engine running, then off.

 

[demarpaint]

Well after a drive a little longer and in warmer temps than the other night, I left the engine running and checked pan temps again. It was a little under 200*F. The fluid is red and the color of new ATF, the level is correct. This is the 08 Liberty in my sig line. I have reason to believe the thermometer is fairly accurate to about +/- 5*F.

 

[Colt45ws]

I was unable to find any temperature increase at the transmission level after shutoff.
I used a SGII to pull the transmission temperature data (TFT) from the computer. I only turned it key on then manually turned on the SGII and waited for it to refresh.
For reference, the sensor is inside the pan and bathed in fluid.
I intended it check a 5 minute intervals for 15 minutes, however I missed the 10 minute check. I also pulled engine cylinder head temperature (CHT) for comparision.
First check is 30 seconds after shut down. It was the same as running just before it was shutoff.
5:39 196CHT, 184TFT
5:44 202CHT, 182TFT
5:54 198CHT, 175TFT

 

[Kiwi_ME]

I don't buy that TC oil "drains." I'll bet it stays right where it was in the TC when shut down. Any temp increase seen at the pan surface is simply a result of the various components reaching equilibrium. Consider that air flow past the pan will keep it slightly cooler than the oil inside, that obviously changes when stopped.

"Latent heat" is not an applicable term for the simple distribution of combustion chamber heat to the coolant on shut-down. See wiki.

 

[demarpaint]

Is there a better way for the DYI guy w/o a SG to check ATF temps other than the laser thermometer I'm using? I'd love to see a comparison between a SG and a laser thermometer aimed at the transmission pan.

 

[hate2work]

Wondering out loud- Frank, could any conclusions be drawn about the accuracy or efficacy of your laser gun if you aimed it at a pan of boiling water? Perhaps from different distances?

 

[demarpaint]

Originally Posted By: hate2work

Wondering out loud- Frank, could any conclusions be drawn about the accuracy or efficacy of your laser gun if you aimed it at a pan of boiling water? Perhaps from different distances?



I was thinking along those same lines Don. Strangley yesterday the oil pan temps were higher, and the transmission pan temps lower than the day before, both instances the Jeep was at operating temps, and nothing really changed as far as driving conditions. I enjoy solving these puzzles and hopefully I'll solve this one with the help of you guys. Next time we boil water I'm going to take some readings from different distances. I always aim for the same spot on the transmission pan when I take my readings. Trav seems to think the readings I'm getting leave a lot to the imagination, and I'm thinking he's right, again!