Second, the engine runs hot when under load. The truck is fitted with a brand new factory FZJ80 radiator, new fan clutch, new thermostat, new thermostat and a very high dollar custom fan shroud but a local sheet metal fabricator. Running easy on flat ground it will stay around 190, but start climbing a hill, or run the speed up and it quickly jumps to 230 or so. I'm stumped, but currently planning to check the pump timing on the engine as one remaining option. Again, suggestions are most appreciated.
I'm a bit new to the 6.5s and have learned a lot from The Truck Stop website (thetruckstop(dot)us). One of the main problems for the 6.5 is cooling, as you already know. Your 230* temps is a SERIOUS problem, should never go over 210*. According to the info I have gleaned, repeatedly letting temps go over 210 will eventually crack the block main webs around the crank cap bolt holes. There are fixes though for this cooling issue. I will try to describe what I have learned, some is my experience and some is others experience.
I have a 94 K2500 Chev pickup with the 6.5TD. A friend at church slid on ice last winter and kissed a tree with it and then helped me get it from his insurance real cheap. I've done a lot of reading and wrenching on it in the past few months and love it.
To start with, do some research on radiators. I don't know what is available for your vehicle, but get the biggest aluminum rad you can stuff in there. According to Bill Heath of Heaths Diesel of Ellensburg, WA the 6.5 prefers aluminum rads as they dissipate heat faster. The rad (aluminum) in my p.u. was damaged in the accident and I found a used brass rad, mistake #1.
The single thermostat coolant crossover was broken also and I found a used newer dual thermo crossover, mistake #2. Mid 96 is when GM went to the dual thermo. Since you have a 96 motor you could have either a single or dual thermo.
The fan blade was damaged also and was replaced with a plastic 9 blade fan from an 01 DMax, good move.
To make the DMax fan fit my water pump I got a new Hayden heavy duty fan clutch from a 97 6.5, double mistake. My first towing trip I got up to about 220* and was down to about 20 MPH up some very short, mild grades and the fan NEVER came on. The second half of that mistake was in not replacing the stock 94 pump for a newer high output pump.
Here is what I found out I should have done.
The rad should have been an aluminum rad instead of the brass rad. Replacing it is still on my to do list.
The coolant crossover would have been best if I had found a single thermo crossover. There are work around fixes for this which is what I have done. Apparently the AC Delco thermostats (from the stealer) are the best ones for coolant flow, from what I have read. This is also on my future to do list.
The DMax fan blade was a good move, but it will not bolt up to the 94 fan clutch which is why I went with the 97 fan clutch. The Hayden HD fan clutch I returned as defective. The stock 94 WP is about 80 GPM flow capacity and the 97 and newer high outputs are about 130 GPM flow capacity. Of the HO pumps the 2000 is the best for balanced flow through the block.
Sooo, here's what I did.
I got a heavy duty, low temp turn on, fan clutch fron Heath Diesel. (I highly reccommend it) I also got a coolant bypass restricter for the dual thermo crossover from Heath. ----heathdiesel(dot)com---- And got the HO balanced flow WP for the 2000 6.5 from a local auto parts store. I don't remember the part number, but I can look it up if you need it.
These mods made a big difference. I recently towed a travel trailer to go hunting. Coming home the last leg took me over Willamette Pass here in Oregon. From Suttle Lake to the top is about 5 miles and about 1500 to 1800 ft elevation rise. I wish I had taken careful note of the exact distance and elevation. Anyhow, it was a good test. The temps went up to 210 and never went over. And I was not light on the throttle either. I stayed as close to the max speed that I could for the corners and traffic.
Some other things to look closely at-----.
Where does your intake air come from? (I need to go back through your whole thread and refresh my memory to see what you have done) If it is from around the motor it is pre-heated before going through the turbo--not good due to higher intake air temps. A cold air intake will help your IAT and EGT. Somebody proir to me or my friend modified my P.U. to have a true cold air intake and I have never seen EGTs over 1150 (EGT guage but no IAT guage). There are other things that will influence EGTs though.
Are you running the stock GM turbo (don't remember)? They supposedly create a lot of backpressure. Making sure you have a free flowing exhaust will help here. Sustained higher EGTs (hills and towing), not just extreme EGT, will transfer heat into the cooling system. I went to a 3" turbo-down pipe that transitions to 4" behind the motor. I don't have any measured statistics, but my butt dyno said it made a difference.
The next mod I have not done yet, but it is on my want to list as it is more expensive. I want to change my stock GM turbo for the A Team Turbo (ATT). It is supposed to give better higher RPM and towing performance and lower EGTs in the process.
Over all, look at your cooling system as any mods there give you more bang for the buck.
Questions? I'll do what I can to help, though I am still learning about the 6.5.
Don
