Just returned from our first camping trip of the year... first tow with the Quadzilla XZT+ (2000 tune). I don’t know if the XZT has any effect on the engine temperature. I am used to to running (empty) right on the thermostat, a needle width below the center mark (200 degrees). Towing, I previously ran about a needle width above that center mark. I saw the temp climb to 2 needle widths above on grades... but came down coasting / light throttle on the other side.

So we arrived at the parking field, shifted to 4 high & were directed to the best spot. They wanted me to circle outside & “drive through” next to another vehicle which I did... but I could not get close enough. I was surprised to notice the temperature climbing to 220. I needed a couple of passes back & forth put the trailer in the right place. Just as I completed the last push back, the temp hit 240 & the RED warning light came on “Check Gauges”. I was in place, so I left the truck running & popped the hood to let the heat out while we set the jacks. The temp dropped to the thermostat level before I shut it off.

I had checked all tire pressures before we left. I checked the belt, all fluids were ok. The ground was spongy... with the sod squishing 3” or so. I was gentle as possible with my stock Michelin tires. I didn’t see any breakthroughs though others mucked up other areas pretty good. We had extreem weather during our stay (a bucket in the truck bed was half full) and the ground was worse pulling out. The property owner had a tracked Bobcat on site & several vehicles had to be extracted.

There was not a row in front of us initially, but later there was. When the vehicle between the trailer & the exit moved, I quickly got my truck into it. We were able to make the exit in one pass... I was gentle on the throttle but didn’t want to stop...

I watched the temps even more carefully on the way home & it was as before... I’d say 200-205. My impression is that the cooling is marginal & that makes me uneasy. I’m planning a thermostat replacement & coolant flush...

I know you guys have more experience than me... Ideas?

Fan Clutch. Being that the temps were OK towing. But as soon as you where crawling around the parking lot there was no wind blowing through the radiator (fan not locking) so it kept rising till it ran to the RED zone and tripped the ... So I would check the fan clutch first...

How do I check the fan clutch?The only other experience with marginal cooling was when I towed my old horse trailer with a GMC 1/2 ton 305 cid... the temp would rise on every grade & come down on the down grade. I replaced the fan with a solid drive flex fan which was a big help. I only see electric fans for the Cummins... Your thoughts on different fans?

Normally the fan makes alot of noise during lock up so if you not hearing a turbo prop your fan isn't working.

Well, at 240* the fan should have been roaring... I think defective clutch is a safe bet. I'm reading that aftermarket fan clutches don't seem to stand up well long term. Having said this, I'm sure I'll hear from some NAPA Lover next.

Well, at 240* the fan should have been roaring... I think defective clutch is a safe bet. I'm reading that aftermarket fan clutches don't seem to stand up well long term. Having said this, I'm sure I'll hear from some NAPA Lover next.

Not I... But you might shop around... I'm sure there is better than NAPA...

The fan clutch is the likely culprit, as Mike said. I would also do the coolant/thermostat to be safe. These trucks are very hard on thermostats due to the size of the cooling system. The 2nd gen thermostats open at 181° and go full open at 203° so some movement when towing is normal, but with a 203° full open you shouldn't go much over 205-210°.One other thing to note is that if the XZT adds timing you will run a higher coolant temp for the same load.

One other thing to note is that if the XZT adds timing you will run a higher coolant temp for the same load.

So does my Edge Comp on 5x5... But I never exceed 200*F towing my trailer... Even pulling 6% grades at 55 MPH. But you sure hear the fan lock up and sound like a turbo prop trying to take off...

I would also do the coolant/thermostat to be safe.

The cooling system is plenty big to handle some of the bigest loads but AH64ID does have a point thermostat and coolant flush is cheap insurance for the summer time.

On my truck I run about 5° hotter for a given load than on stock timing. The size of the cooling system is part of the reason these motors are hard on thermostats, they rarely go full open so the shafts develop wear spots and the springs fatigue. I replaced my thermostat 16K miles ago, of which a good amount has been towing, and the thermostat has only gone full open 4-5 times at best (honestly I can only think of 2)...

Just pulled around 700 miles over the past week, today was almost 100F outside. I DON'T run a fan, even pulling our trailer which probably all added up to 6k lbs this time and I beat the crap out of it at 70mph the entire time. Coolant runs around 200F but up some 7% grades I was seeing 205, maybe more. It may have hit 210 when I was going up a 7% grade at 60 and was accelerating to 70 up the hill in 5th (passing dump truck). Going slow (under 10mph) is the only time I saw an issue, and it was a slow heat rise issue. The heater actually pulls all the heat the engine produces at <10mph. It's not the greatest to be running the heater full blast on a 100F day but it does the trick I got a plan B in the works that will top any fan.Checking the thermostat would be my top priority in your case, then clean the radiator fins if they are dirty, then check the fan. One of those will surely be the culprit.

Make sure the radiator is clean, to me thats step one. Check the fan clutch as well. Check coolant level in the overflow tank. I only use cummins thermostats. I used redline "water wetter" and it will drop your coolant temp. It worked in mine. http://www.redlineoil.com/Products.aspx?pcid=10 When i am in 4whigh and have a heavy load it puts more heat into everything. Maybe try 4 low. Just make sure you hit the breaks good to avoid the clunk when shifting. I have a good water pump do you want to try it to see if there is a difference?

In addition to the above, you might want to consider pressure washing out the radiator being careful to use a reasonable amount of pressure and spray pattern (wide) and blow the radiator out with compressed air. You would be amazed at the amount of bugs and crud that builds up in there.