Every website has an opinion one way or the other on the trans heat exchanger. So, what is the consensus here? Do I replace it or delete it and put a under bed cooler on it?

I would say keep it and replace the damage heat exchanger for the transmission.

The factory heat exchanger not only cools transmission fluid, but all so heats the fluid to operating temperature in cold weather.   With the average winter low temperature of 9°F in your area it would be prudent to retain the heat exchanger for winter drivability.

Could a guy put a full flow directional valve in diverting the fluid either through the block mounted cooler during winter months and then shut the valve during summer months? Maybe run the summer hose circuit through a derale cooler with fan under the chassis? 

I recommend keeping the heat exchanger but replace the OEM unit with the one Full Send Diesel designed, which is an all-billet solid unit with two totally separate areas which cannot rupture and cause crossover contamination between the coolant and the trans fluid. These units also cooler far more efficiently due to being solid billet design. Combine this unit with their heavy duty high flow transmission cooler and your transmission will remain cool even in the most extreme conditions. My coolant temps with sensor in the deep pan never gets above 150 degree in the month of August in Florida.

Yeah, up here in Idaho, we see upwards of -20℉. Automatics up here are rather rare, and manuals are more typical. The guys here are right that you should consider keeping the factory transmission fluid cooler or replacing it with a more modern transmission cooler in its place. The factory cooler has issues with rusting and leaks over time.

On 12/31/2025 at 9:57 AM, Mopar1973Man said:

Yeah, up here in Idaho, we see upwards of -20℉. Automatics up here are rather rare, and manuals are more typical. The guys here are right that you should consider keeping the factory transmission fluid cooler or replacing it with a more modern transmission cooler in its place. The factory cooler has issues with rusting and leaks over time.

I'm in southern MN, we also see temps like that regularly. my other 2 are manuals, but the family fits in this one. The biggest reason I'd like to keep this truck an auto is because its meant to be the camper hauler. Some of the campgrounds its just way easier backing in with an automatic. That being said, when i got in to go to work one day the truck just wouldn't move at all anymore. Changed the governor pressure solenoid and sensor to no avail. i'm not sure what to check further, haven't taken the time to research it. thinking of just pulling the trans and rebuilding it in my basement, possibly swap it to a full manual valve body.

I have my 48RE built heavy duty at a local shop which specializes in 48REs which cost about $6K and is now capable of towing the truck's maximum weight and also can handle 1000 hp. However, my truck will never have more than 650 hp, if that. The 48RE when built correctly addressing all known weaknesses is an excellent transmission. I added a Full Send Diesel trans cooler unit which keeps the fluid temps in the 120-140 degree range.

6 hours ago, DPD said:

I have my 48RE built heavy duty at a local shop which specializes in 48REs which cost about $6K and is now capable of towing the truck's maximum weight and also can handle 1000 hp. However, my truck will never have more than 650 hp, if that. The 48RE when built correctly addressing all known weaknesses is an excellent transmission. I added a Full Send Diesel trans cooler unit which keeps the fluid temps in the 120-140 degree range.

Any idea what could be the problem with mine suddenly? Drove fine in the morning. Went to leave for work that evening and it won't move in any gear. Changed the governor pressure solenoid and sensor to no avail