The other day I came out of Death Valley to Beatty which is long and steep, but not that bad, but the transmission temp got up to 230 for most of the trip. I stopped part of the way up and let it cool before going on. This has happened a few time in the past, but I am looking to add a additional cooler if for nothing else make me more comfortable. The truck is a 2003 Dodge Cummins with less than 160,000 on it, and runs great. I would like to find an add on cooler that would not cost a mint and be an easy application to take care of this in the future. I have had it 15 years and other than this it has been a great truck. There doesn't seem to be a lot of room with coolers attached to the radiator now. Anyone have any suggestions? Thanks, Mike.

After 15+ years, the radiator is probably not all that great anymore (I'm in the same boat). I would ensure it's performing at 100% before adding coolers - or, just replace it. With your current TT there's no way you should need more trans cooling. Then add a couple of bottles of "Water Wetter" and change the coolant. I would also have the trans serviced and have the shop verify the torque converter is locking up. If it doesn't, it adds a ton of heat.If you end up with another cooler, don't go cheap. You really get what you pay for with them and what ever you do, don't bypass the stock cooler.

To the OP.What was your engine coolant temperature? Also what was the ambient temperature? What was your speed and engine RPM?

230F is not overheating the trans.That said; Scott's ideas are good and it also would be nice to get a little more info on the ambient temp and RPM ect.

Like mentioned I would make sure everything is nice and clean before doing anything else!!!

230F is nothing for transmission fluid ! I worked design transmission over 30 years ago and even then we never got worried until the temp were above 275F ! Most fluid now a days is semi-synthetic or full synthetic so it is good for more than that.

Truck overheating towing on long steep grades. | Good Sam Community

Cummins12V98
Explorer III
Mar 27, 2020
I always towed by the pyrometer on my 98 12V. Lots of pedal left but all I would have done was burn up #6.
time2roll
Nomad
Mar 27, 2020
I agree dropping one more gear and running part throttle and keeping the RPM up is the best plan if the temp gauge is rising uncomfortably. Generally I recommend RPM between peak torque and peak HP when pulling max.

For an older truck it might be worth while to replace the radiator. And if the TC does not lock in second and this is an option to fix with a chip I would go for that. Just don't use the chip to make more power as that can only make things worse. I don't recommend anything that would defeat emission controls.
Grit_dog
Navigator
Mar 27, 2020
SweetLou wrote:
This maybe an ignorant question, but when I had my '97 and '05 cummins, I monitored my exhaust temps closely. If I stayed at 1000 to 1100 degrees and no higher, I could climb any grade at any tme without heating issues. I had a manual trans in both, and I realize that this is not the same animal that the OP is asking, but trans temps are related to how much you have your foot in the truck as well right? Gear down, get the fan to spin higher, and it just goes. 16 miles of the Baker grade at 117 degrees outside was never an issue even with windows open. Like I said, I may not be correct here, but if I am, then possibly adding an exhaust temp gauge is all that is needed along with cleaning the coolers.

EGT gauge is handy, albeit unnecessary for a stock truck.
I'll presume your statement above, the 1000-1100 degrees is a post turbo EGT? If it's preturbo temps then you were limiting your right foot input to about half the safely available output.
ppine
Explorer II
Mar 27, 2020
On steep roads like going to Death Valley your engine and your brakes are going to get hot when towing. Get used to it and pull over.
Cummins12V98
Explorer III
Mar 26, 2020
100% agree! Drop a gear and back out of the throttle, does wonders.
SweetLou
Explorer
Mar 26, 2020
This maybe an ignorant question, but when I had my '97 and '05 cummins, I monitored my exhaust temps closely. If I stayed at 1000 to 1100 degrees and no higher, I could climb any grade at any tme without heating issues. I had a manual trans in both, and I realize that this is not the same animal that the OP is asking, but trans temps are related to how much you have your foot in the truck as well right? Gear down, get the fan to spin higher, and it just goes. 16 miles of the Baker grade at 117 degrees outside was never an issue even with windows open. Like I said, I may not be correct here, but if I am, then possibly adding an exhaust temp gauge is all that is needed along with cleaning the coolers.
LITEPHIL
Explorer
Mar 26, 2020
That's probably nothing to worry about at all. I've towed the same hills here in Arizona for many years and EVERY one of my trucks temp would go 3/4 the way up and the transmissions would go to at least 230 on the long climbs. That's another reason to use synthetic fluids. On my 06 Dodge Cummins I did install a Mag-hitec deep transmission pan to be safe.
garyp4951
Explorer III
Mar 24, 2020
The 2003 5.9 Cummins had an additional torque converter cooler mounted on the driver side at the rear on the engine, and I would check this also.
As stated before, replacing the vicious fan clutch with only oem did the trick for me.
Cummins12V98
Explorer III
Mar 23, 2020
Someone besides me please confirm but the 3rd gen 4 speed auto does NOT lock in 2nd???

I know it can be made to be.
FishOnOne
Nomad
Mar 23, 2020
time2roll wrote:
Cummins12V98 wrote:
If you were doing 35 you were unlocked in 2nd gear!
No lock in second gear? That seems like bad design to me.

The entire life span of the torqueflite was a bad design