DBF

The heat exchanger on my truck failed also. I added another fan-driven-cooler under the bed on the passenger side equivalent to the Dodge Superduty fan-cooler on the drivers side. Took out all the plumbing that had to do with the heat exchanger.

The two fan-driven coolers (with sensors and switches to turn on the fans) keep the trans cool except when towing the 7500# 5er in 95* heat.

Next, I'll improve the little cooler on top of the radiator - it's time to replace all those hoses anyway.

Regards, DBF

scottmn1

That Cummins external cooler is a very good one. One thing you may have trouble with in the winter months if you live in the northern areas is keeping your fluid "warm enough" if you remove the original cooler that dissipates the trans fluid heat to the coolant, and also dissipates the coolant heat to the trans fluid when it is real cold outside.. I put an auto trans behind an engine that originally had a manual trans, so I didn't have the original Cummins cooler. So I bought the biggest trans cooler with a cooling fan Perma Cool made, but until I installed the Cummins fluid to water cooler that is installed originally, I had trouble keeping the trans fluid cool enough in the summer(when hauling loads), and warm enough in the winter. I found the best for me was to use the original Cummins cooler first, then run it through the big Perma Cool cooler with the fan to kick on if the temp crept up too high for added insurance. The optimum trans temp is to be close to the coolant temp of your engine, which is somewhere between 180-200 degrees, which is why that original Cummins cooler works real good because it keeps the fluid about the same as your coolant to begin with. They always say that keeping your trans fluid as cool as you can is what you want to do, but too cold will keep the transmission from shifting good and smooth. You want the fluid to stay good and warm, but try to keep as low as you can over 200 degrees. Sometimes for me on very hot days pulling a heavy load, going up a hill at low speeds it will be impossible to keep it from creeping up there near 240 degrees, but my combination of coolers won't let it get that way very often, or for very long. There are some pretty good charts floating around on the internet that shows how high trans fluid temperatures decreases the life of your transmission because the heat destroys the lubricication efficiency of the fluid which in turn will decrease the life on the transmission. The higher your trans temps run, the more often you need to change the fluid. Anyway, that combination works the best for me, but then I am always hauling a pretty heavy load. Just my thoughts.

DBF

Your comments above are absolutely correct. Everyone with an auto should read them and keep them in mind.

But I live in Florida, so I don't have the winter problem. If I had to move back up north, I'd find a new engine-coolant-to-trans-fluid heat exchanger for its cold-weather benefits. There are several on the market.

Helping my exchanger-less situation, there is a bypass in front of that Superduty under-the-bed cooler that allows fluid being pumped to that cooler to go directly to the return line; when it's cool, a good bit of the fluid just goes back to the front cooler & then the transmission.

Without the heat exchanger, one can really see the trans fluid temp rise quickly in stop-and-go traffic. Sitting still on a warm day with your foot on the brakes and trans in "D" heats up the fluid rapidly. Then, around 180*, the fans come on and it goes back down soon.

I do change fluid earlier than normal if I've done any high-temp work; I printed one of those graphs & keep it in the truck.

Regards, DBF

jw216

I think I would call Bill at DTT (1-866-504-4002) and see if he has an authorized shop in the area, let them do what they do. Then try to enjoy trip!

Loopi

I honestly would absolutely LOVE to call Bill at DTT, but I am pretty sure Bill won't take my good looks as currency since A> they aren't THAT good, and B> I've known most places to want money. Since I have so far spent about $2700 getting this going, and I have a newly rebuilt trans with a FULL warantee if I can just get it to Phoenix from San Diego 300 miles over mountains, I don't really find the Bill at DTT suggestion helpful right now.

Thanks tho,
James