Transmission fluid too hot.....

[Grmoore1964]

Had my 3000# camper in the bed of my truck today. Drove about 4 hours - mostly flat - and didn't have any problem. Tow/haul selected w/exhaust brake. Started up the hill outside Gresham,OR over Mt Hood and had the 'Transmission Fluid Too Hot' alert chime. Followed the procedure in the users manual to cool it off - idled in neutral. Saw temp spike to <300, then shut it off. Let cool a while and drove to the Ram dealer in Gresham.

Any thoughts? Happened after a stop for lunch and fuel. Glad I didn't press on over the hill - over temp ligh back on 6 miles later at the dealer. Hoping for an easy fix...

btw, Aisin transmission.

Thanks -

Greg

 

[rrl989]

I wonder if there is some kind of flow control issue going up to the coolers, maybe a plugged check valve? My Aisin empty normal temp if I recall correctly is in the 160's F

 

[Grmoore1964]

It sounds like that is exactly the problem. Apparently there is a check valve in a transmission line that is causing too much restriction. If I recall correctly, my empty transmission temp is in the 180-190 range although I've seen it as high as 230 empty. Today, on flat ground loaded I was seeing in the 260's. It seems the overtop alert comes on at 285. I pulled over and watched it climb to where it indicated <300 - not a specific number.

This dealer in Gresham has been extraordinary. Sounds like they are going to rob a part from an inventory truck and get us on the road yet today. Plus refill the 20 quarts of fluid - I probably cooked it a little.... I can't tell you enough good things about them - great place to be stuck!!

 

[rrl989]

I previously loaded my 4000lb Arctic Fox truck camper, drove it pretty hard and my temps never really moved above my normal. Sounds like an easy dealer fix for you.

 

[Wertles]

Very interesting. I have yet to see anything over 200, even pulling 18,000 pounds up hill.

 

[transe]

You did the right thing in stopping to let it cool off. I wouldn't be too concerned about a one-time overtemp event.

In the Aisin trans, there are actually TWO temp sensors: one in the sump, and one in the "T/C out" ("to cooler") passage. The temp reading that you see in the EVIC is the sump temp, but the "trans overtemp" light is actually triggered by the T/C out temp (which, in situations like hauling a load up a steep grade, can be significantly higher than the sump temp). The "trans overtemp" light comes on when T/C out temp hits 145°C (293°F). At that point, your sump temp is still usually well below this. Yes, 293°F is hotter than you want to run, but brief spikes to this level will not do significant damage to the trans.

As you sat idling in Neutral, you were pumping the hot oil out of the converter (through the cooler, and into the sump). I'm guessing that's why you saw the indicated trans temp (sump temp) continue to rise (because the hot oil in the converter was getting pumped into the sump).

The T/C out temp can rise very rapidly in conditions of high converter slip and high torque. Since you stopped right away, you eliminated the source of the heat, thereby preventing any further escalation (in the T/C out temp; as I noted the sump temp may continue to rise as hot oil from the converter gets mixed into it). In the future, you can help to reduce the amount of heat generated (in the converter) by shifting down to the lowest gear possible when climbing a steep grade at low speeds, and by shifting the trans to Neutral when stopped in stop-and-go traffic.

So bottom line, I doubt there is anything wrong with the truck. You probably just spiked the T/C out temp during the long climb up the grade. Your response was perfect, and your trans should be fine.

 

[gsbrockman]

In the Aisin trans, there are actually TWO temp sensors: one in the sump, and one in the "T/C out" ("to cooler") passage. The temp reading that you see in the EVIC is the sump temp, but the "trans overtemp" light is actually triggered by the T/C out temp (which, in situations like hauling a load up a steep grade, can be significantly higher than the sump temp). The "trans overtemp" light comes on when T/C out temp hits 145°C (293°F). At that point, your sump temp is still usually well below this.

Interesting information....thank you !!!

 

[Grmoore1964]

You did the right thing in stopping to let it cool off. I wouldn't be too concerned about a one-time overtemp event.

In the Aisin trans, there are actually TWO temp sensors: one in the sump, and one in the "T/C out" ("to cooler") passage. The temp reading that you see in the EVIC is the sump temp, but the "trans overtemp" light is actually triggered by the T/C out temp (which, in situations like hauling a load up a steep grade, can be significantly higher than the sump temp). The "trans overtemp" light comes on when T/C out temp hits 145°C (293°F). At that point, your sump temp is still usually well below this. Yes, 293°F is hotter than you want to run, but brief spikes to this level will not do significant damage to the trans.

As you sat idling in Neutral, you were pumping the hot oil out of the converter (through the cooler, and into the sump). I'm guessing that's why you saw the indicated trans temp (sump temp) continue to rise (because the hot oil in the converter was getting pumped into the sump).

The T/C out temp can rise very rapidly in conditions of high converter slip and high torque. Since you stopped right away, you eliminated the source of the heat, thereby preventing any further escalation (in the T/C out temp; as I noted the sump temp may continue to rise as hot oil from the converter gets mixed into it). In the future, you can help to reduce the amount of heat generated (in the converter) by shifting down to the lowest gear possible when climbing a steep grade at low speeds, and by shifting the trans to Neutral when stopped in stop-and-go traffic.

So bottom line, I doubt there is anything wrong with the truck. You probably just spiked the T/C out temp during the long climb up the grade. Your response was perfect, and your trans should be fine.

Thanks for the great info! Still camping in the lot of the Greaham Ram dealer - they just got approval to rob the part from a donor truck to get us on the road.

A couple things. First, we were barely headed uphill at all when this occurred the real steep stuff is yet to come. My point is, it didn't seem to be lugging the engine at all and since the tow/haul button was pressed, I was under the impression that the T/C should have been locked up with no slippage. Shouldn't the cooler be able to dissipate the heat from that? We had gone about 6 miles from the fuel stop when the over temp light chimed. I'm concerned that maybe this line/check valve assembly isn't the problem at all and there is some other reason for the temp to have spiked. I don't feel like it was operator error - the load isn't that heavy and we had barely started up a slow climb. So, when we get on the road again I'll monitor the temp closely, and shift to a lower gear. Short of that, I'm kind of at a loss for what to do.

Thanks again - I'll keep the board updated as I learn more!

Greg

 

[transe]

Yes, if you're at highway speeds (40-45 mph or higher) the TCC should be engaged, which should help keep things cool. The typical problem is at lower speeds (~25 mph or less), where there is little airflow and where the TCC may not be able to remain engaged.

But if you're seeing a consistent temp problem, then yes, it is possible for the thermal bypass valve (TBV) in the cooler lines to be stuck (in the bypass position, so little or no oil goes to the cooler). Find your TBV (it looks like a block of aluminum somewhere in the middle of the cooler lines) and check the temp (carefully!) of each line. Once things are warmed up, the inlet and outlet on each side of the TBV should be equal in temperature. That is, the line coming from the trans (into the TBV) should be the same temp as the line coming out of the TBV and going to the cooler. Likewise, the line coming from the cooler (which should be cooler!) and into the TBV should be the same temp as the line going from the TBV back to the trans. If the "cooler to TBV" line is cool, but the "TBV back to trans" line is hot, then you have a stuck TBV. I believe the valve itself can be removed from the block (and replaced) without removing the whole TBV from the cooler lines.

 

[Grmoore1964]

Yes, if you're at highway speeds (40-45 mph or higher) the TCC should be engaged, which should help keep things cool. The typical problem is at lower speeds (~25 mph or less), where there is little airflow and where the TCC may not be able to remain engaged.

But if you're seeing a consistent temp problem, then yes, it is possible for the thermal bypass valve (TBV) in the cooler lines to be stuck (in the bypass position, so little or no oil goes to the cooler). Find your TBV (it looks like a block of aluminum somewhere in the middle of the cooler lines) and check the temp (carefully!) of each line. Once things are warmed up, the inlet and outlet on each side of the TBV should be equal in temperature. That is, the line coming from the trans (into the TBV) should be the same temp as the line coming out of the TBV and going to the cooler. Likewise, the line coming from the cooler (which should be cooler!) and into the TBV should be the same temp as the line going from the TBV back to the trans. If the "cooler to TBV" line is cool, but the "TBV back to trans" line is hot, then you have a stuck TBV. I believe the valve itself can be removed from the block (and replaced) without removing the whole TBV from the cooler lines.

The saga continues. They put a new TBV from a truck in the lot. They have been unable to get the valve to open and allow ATF to get to the cooler even after warning it up to normal temps (high 180's on the EVIC. Additionally, they tried to blow air through the cooler and aren't getting any flow. They are currently tring to bypass the valve altogether and run the fluid from the transmission directly to the cooler and back. If that works, they'd like to send us on our way for the weekend.

How hot must the fluid get before the TBV opens? Is there another thermal valve someplace up in the cooler itself?

thanks for all your help - you've provided fantastic information.

Greg

 

[MattandLana]

...

This is fantastic information for all of us if we ever strike a problem. Many thanks.

 

[transe]

I don't know the exact specs, but typically I'd expect the TBV to start opening (sending fluid to the cooler) at about 160°F, and to be fully open by about 180°F. There is no other valve in the cooler itself, that I'm aware of.

 

[rrl989]

Hard to believe the TBV is mechanically controlled by temperature with all the computer controls on our trucks.

 

[Grmoore1964]

I wanted to give an update to the resolution of my problem. They were able to get the TBV that was robbed out of the inventory truck to flow at around 170. However, the transmission cooler in my truck would not allow compressed air to pass. They put compressed air on the cooler from the truck they robbed the TBV out of, and it freely flowed, so at that point we knew that there was something plugging my cooler. They swapped the cooler from the donor truck in and immediately the problem was solved. The interesting thing is that when they were looking through their technical pubs on the computer, there was reference to a second thermostat located inside the cooler. We couldn't find anything that looked like it could be a thermostat. I don't believe there is one in the cooler itself. After the repair, we put over 700 loaded miles on the truck and the transmission temps stayed between 177 and 179 even over mountain passes.

We never were able to get anything out of the old cooler to see what was plugging it. I suspect that it was a manufacturing defect and had been that way since new. Since I had never loaded my truck up, I never generated enough heat to trigger the EVIC alert. The other possibility is that there has been something coming apart in this transmission over the 3200 miles prior to the alert that eventually plugged up the cooler. I kind of don't think that is the problem as the fluid seemed clean, although burnt from the high temps of the original over temp. At the suggestion of the service manager at Gresham Ram, I contacted Ram about extending the warranty on the transmission since this is a possibility. I'll post something when I learn if that was successful.

Lastly, I can't say enough positives about the Gresham Ram service department. They worked feverishly to get us on the road on Thursday and Friday before the Holiday weekend. They took a brand new truck out of inventory and robbed parts off of it. At times, there were 4 people including the service manager working to solve this problem. They loaned us a truck and were ready to loan it to us to continue our trip with a borrowed trailer. All in all, it was service well beyond anything I could have ever dreamed of from a truck dealer. If you are ever stuck or are anywhere near them and in need of service, I couldn't give them a higher recommendation.

Thanks to all on here sharing their knowledge, especially TransEngineer. What a great resource when you are in need!

Greg

 

[Too Tall]

It's a shame you are having this issue with a brand new truck. That sucks. Hopefully, you'll be good for a long time.