transmission temperature ?

[sawtooth]

Unforunately, posted the following on the Motor Home Board.

Last fall replaced my old RamCharger (RC) with a newer vehicle to pull my new travel trailer. The old RC has a short wheelbase, high center of gravity, too many miles and semis blew it all over the road when passing going 80 MPH.

The Trailer: '05, Fleetwood, Pioneer; 22', advertised dry WT. 3,647 LBS, actual WT. 5200 LBS with our extras (air, awning, ETC), dry tanks (gray, black, & water), and all our stuff.

The Truck: "96 Dodge 1500 (1/2 ton), 4-wheel drive, 5.9L (360), 3 SPD. Auto with overdrive, and lock-up torque converter, 3.55 DIF, (oversized tires give a gear ratio of 3.22), GCWR 12,500, and Max Trailer Wt. 7,700. Tranny fluid flow on this vehicle is torque converter output to radiator, radiator to tranny cooler ( mounted fwd of radiator) and then to the tranny pan.

After reading about all the troubles Dodge & other manufactures have had with auto trannys since they stopped using whale oil, I sought the advice of some experienced RV'ers. One fellow, who has made a couple of 360 DEG trips to Alaska, told me to keep the torque converter in lock when ever possible to reduce heat. Another fellow told me to install a temp. gage at the output of the torque converter and drive for the lowest temp.. So I pulled the tranny pan, installed a drain valve, & a new filter. 200 miles later, drained the tranny fluid and refilled. Installed an oil temp. sensor VIA a T-fitting between the torque converter output and the radiator. (tested the gage and sensor in boiling water to determine accuracy).

Our trip: Boise to Glenns Ferry, ID, freeway, , tranny temp was 140 on the flats but hit 220 on some 6% grades before I dropped into 2'nd. Glenns Ferry to Stanley,ID, temp reached 250 about 1/3 up Galina Pass (8700ft) dropped into 1'st and temp decreased to 210 before the summit. ( the torque curves on this truck are relatively flat between 2000 and 4800 RPMs, my max rpm is around 3500). Stanley to Salmon,ID, temp never reached 140, stopped to trouble-shoot gage and then realized following the Salmon River East was down hill. Salmon to Darby, MT, 8500 ft pass same results as Galina.

My scheme of increasing RPMs , keeping a lot of transmission fluid flow worked well until we reached Lewiston, ID (750f). Pulling out of that area the temp gage hit 230, dropped to 2'nd( temp gage 240), dropped to 1'st (temp gage 250), the radiator temp gage approached 230 (normal is 200). Dropped to 4-low and temp readings seem to hold until we found a turn-out.

So how do fellows keep your tranny cool?
Does tranny fluid start to varnish and lose its lubricating properties at high temperatures?
Should I remove the gage and drive pedal to the metal?

[sawtooth]

Unforunately, posted the following on the Motor Home Board.

Last fall replaced my old RamCharger (RC) with a newer vehicle to pull my new travel trailer. The old RC has a short wheelbase, high center of gravity, too many miles and semis blew it all over the road when passing going 80 MPH.

The Trailer: '05, Fleetwood, Pioneer; 22', advertised dry WT. 3,647 LBS, actual WT. 5200 LBS with our extras (air, awning, ETC), dry tanks (gray, black, & water), and all our stuff.

The Truck: "96 Dodge 1500 (1/2 ton), 4-wheel drive, 5.9L (360), 3 SPD. Auto with overdrive, and lock-up torque converter, 3.55 DIF, (oversized tires give a gear ratio of 3.22), GCWR 12,500, and Max Trailer Wt. 7,700. Tranny fluid flow on this vehicle is torque converter output to radiator, radiator to tranny cooler ( mounted fwd of radiator) and then to the tranny pan.

After reading about all the troubles Dodge & other manufactures have had with auto trannys since they stopped using whale oil, I sought the advice of some experienced RV'ers. One fellow, who has made a couple of 360 DEG trips to Alaska, told me to keep the torque converter in lock when ever possible to reduce heat. Another fellow told me to install a temp. gage at the output of the torque converter and drive for the lowest temp.. So I pulled the tranny pan, installed a drain valve, & a new filter. 200 miles later, drained the tranny fluid and refilled. Installed an oil temp. sensor VIA a T-fitting between the torque converter output and the radiator. (tested the gage and sensor in boiling water to determine accuracy).

Our trip: Boise to Glenns Ferry, ID, freeway, , tranny temp was 140 on the flats but hit 220 on some 6% grades before I dropped into 2'nd. Glenns Ferry to Stanley,ID, temp reached 250 about 1/3 up Galina Pass (8700ft) dropped into 1'st and temp decreased to 210 before the summit. ( the torque curves on this truck are relatively flat between 2000 and 4800 RPMs, my max rpm is around 3500). Stanley to Salmon,ID, temp never reached 140, stopped to trouble-shoot gage and then realized following the Salmon River East was down hill. Salmon to Darby, MT, 8500 ft pass same results as Galina.

My scheme of increasing RPMs , keeping a lot of transmission fluid flow worked well until we reached Lewiston, ID (750f). Pulling out of that area the temp gage hit 230, dropped to 2'nd( temp gage 240), dropped to 1'st (temp gage 250), the radiator temp gage approached 230 (normal is 200). Dropped to 4-low and temp readings seem to hold until we found a turn-out.

So how do fellows keep your tranny cool?
Does tranny fluid start to varnish and lose its lubricating properties at high temperatures?
Should I remove the gage and drive pedal to the metal?

[Vette Racer]

My thinking is where you have the sending unit. Most sending units I've seen are placed in the transmission pan, not on the output line. I believe you are seeing spikes due to the location and you need to monitor the fluid in the pan to get a more accurate and steady reading. Keep in mind that if your speed falls below 30-35 mph you are not getting much airflow over your cooler and would benefit from a fan placed on your cooler operated by either a switch you can actuate manually or by a temp sensor. I prefer the switch so I know and have control of when the fan is on. Had this setup on a motorhome. Normally I would like my trans temp to stay below 225. Thats my opinion, others may differ. As to your last question, yes, heat kills. For the most part, lower is better.

[jperry29]

This subject has a lot of history. I did a search and found one of my favorite replies. I think this discussion has some really valuable information.

Tranny Temps

[Wilber1]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">My scheme of increasing RPMs , keeping a lot of transmission fluid flow worked well until we reached Lewiston, ID (750f). Pulling out of that area the temp gage hit 230, dropped to 2'nd( temp gage 240), dropped to 1'st (temp gage 250), the radiator temp gage approached 230 (normal is 200). Dropped to 4-low and temp readings seem to hold until we found a turn-out. </div></BLOCKQUOTE>

Wonder how high the temperature would have gone if you hadn't shifted down. True, the flow rate will be greater at a higher RPM but giving the transmission a greater mechanical advantage with lower gearing is what really helps it out. There comes a point where it can no longer cope and the only thing you can do is decrease weight, increase cooling or go to a lower rear end ratio. A 4.10 ratio increases the tow rating and GCWR by 2000 lbs on the diesel trucks and the transmission is the limiting factor.

[Mark Kovalsky]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sawtooth:
My scheme of increasing RPMs , keeping a lot of transmission fluid flow worked well until we reached Lewiston, ID (750f). Pulling out of that area the temp gage hit 230, dropped to 2'nd( temp gage 240), dropped to 1'st (temp gage 250), the radiator temp gage approached 230 (normal is 200). Dropped to 4-low and temp readings seem to hold until we found a turn-out.
</div></BLOCKQUOTE>
That's why I installed my gauge in the test port. The test port will give just about the same temp as the pan.

The outlet to the cooler is the hottest point, but it isn't the most important point. As you discovered when the torque converter is unlocked it makes A LOT of heat. The coolers are removing most of that heat, and if you had had a sender in the trans instead of the cooler line I'm sure you would have seen much cooler temperatures.

250?F isn't a dangerous temperature for modern ATFs, as long as it isn't for a real long time. The fluid can withstand excursions up to 275?F with no trouble for the time it takes to get up a grade. If you want to keep the sender in the cooler line I wouldn't worry until I saw over 275?F.

Instead of removing the gauge I recommend moving the sender to the pan or a port on the case. That will give much more useful temperatures. The temperature I worry about is the bulk temp of the majority of the trans, not the peak in a cooler line. In this location start keeping an eye on it at 220?F, and stop to cool if it gets above 250?F.

The correct way to cool a trans is to have it in park or neutral (Dodge requires neutral, not park to flow to the coolers) and run the engine at 1200-1500 RPM. Don't shut it off untill it cools off. Shutting the engine off with the trans hot can cause heat soak to make parts inside get MUCH hotter before cooling, often causing damage.