1988 k3500. 6.2/TH400/NP241. 14 bolt semi float. Pm me your email and I can tell you more.
Yes, speeding up the water pump probably would help. I’m kind of stuck in “in between land” on this issue. Square body truck designed for gasoline engines, Diesel engine designed for 55 mph speed limits without over drive, radiator also designed for 55 and no OD. Add in the Banks turbo kit, my 35” tires and 3.73 gears. I expected issues.
However, my design goals put me here. Highway cruising at posted speed limits up to 85 mph while getting as close to 20 mpg as I can. For sure 20 plus mpg at 65-70 mph driving. All with ice cold air conditioning and other comforts. Then, be able to pull 10,000 pounds up to 65 mph and get 10 mpg doing it.
I haven’t finished wiring in a mode switch button for the Compushift TCM. When I do, that will be my “Tow/Haul” button in effect since the 4L80E didn’t have that option. I have spent my efforts getting the normal driving mode set like I want. Normal commute driving has all shift around 1800 rpm with lock up only in OD at 47.5 mph. Basically, I am lugging the engine taking advantage of the high compression low end torque the turbo isn’t needed for.
Since a 6.2 and na 6.5 both make max torque in the 1,800-2,200 rpm range, I made the truck to keep the engine there. Without a turbo and the egt rise when the boost comes along. I probably wouldn’t have any coolant issues. I wouldn’t go up any hills at speed either. Normal cruising has around 1 psi boost and 400°-450° egt at 60 mph. Aerodynamics starts to beat me up as the speeds get higher. 2-3 psi boost and 500°-600° egt at 75 mph. Followed by a steady rise in coolant temperature.
More coolant flow and faster fan clutch ratio speed I think are what is needed. I started driving the truck with the Delco HO water pump and a 20 year old stock GM fan clutch. 50 mph was all I could cruise at when outside temps were over 90°.
I covered this in depth back in June many post ago. But, I added a Heath Diesel medium duty fan clutch and 21” fan. It was a half measure, I knew it was at the time and yet I did it because I didn’t want to spend the larger amount for the heavy duty option. Or, change the water pump out again. The half measure got me almost where I wanted, but as posted above. Not all the way. In a non OD CUCV. I am sure what I have now would be more than enough. Same thing in a rounder GMT-400 body style truck. Maybe even swapping to 4.11:1 gears would do it. Another water pump and heavy duty fan clutch is a lot cheaper than swapping in CUCV axles. I might end up there some day, but only after I take the steps between here and there. I’m stubborn that way.