Motorad thermostats are fine, a thermostat is either open or closed. If you see dry coolant around the housing the gasket is probably seeping. In SETX on my 98 LSE for example that I drove daily for a bit temps were as followed Highway 188-195F at 65-75MPH, idle in a drive thru with the HVAC on full blast I would see it get up to 212F (206-212F depending how long I sat in line), but once I was on the road 188-193F. That was with a 180F thermostat, 2 good efans, new fan blade, new fan clutch, new radiator, and new hoses.

These trucks DO NOT like to sit at idle for very long (small grill opening). Temps will climb in warmer climates for sure. My 97 XD out on a trail run in 2019 hit 220-226F out on the trail when I was down in a tight creek bed and stuck at idle while someone 5 vehicles up was having issues with a part of the trail. I got out of the creek bed finally, and popped the hood to let her cool down. The HG's were already seeping on that truck when I bought it, and 4 months after that event she started leaking badly from the bank 2 rear water jacket area. Did a HG job and she's up and running again with zero issues. Usually out on the trail I'll keep it in a lower gear to let the RPM's be higher than usual and that's enough to let the fan clutch fully engage and keep it cool at slower speeds. That creek bed was just a poor spot with no air flow, and the only air floating around was already being warmed up by the LR's which were surrounding me F/R.

 

Mine seems to run right around 195-200 on cool days below 70 F, and on warmer days, it only ventures hotter when driving at 65-75 MPH and only when giving it a heavy bit of gas. Temp gauge on dash goes up above 1/2 to 3/4 , OBDii scanner reads 220-235 and I slow down to let it cool off. Only happens at higher speeds and warmer temps. Been doing this for about a year, running the heater on high does make a bit of difference. gets 17- 20 mpg so I don't think it is a head gasket, possibly a radiator(??)

 

This has been my experience as well. Same setup. Same temps. Sitting at idle is challenging for these trucks. A little throttle (in neutral) to get the fan moving helps.

 

Dude - just lay off the drive thru

LOL

 

Here's a sad related story. My coolant reservoir split after a slow trek across the sand on a hot day. Turns out the fan clutch was toast.

If the fan roars for the first few minutes after starting in the morning, then gets quiet a way down the road; that is a good fan clutch at work. As it heats up, the fan should roar again. If the fan never roars, it is toasted. If it is covered with the fluid that came from inside it, it is toasted. I saw a demo on-line to test the fan clutch with a rolled up newspaper. If the news paper stops it, the clutch is toasted. The fan clutch is not too expensive and fairly easy to change and does not last forever, so that's where I would pay attention to. A new fan clutch is nice for peace of mind too.

The electric fans work with the air conditioner on my trucks. They turn on whenever the A/C is on. Super easy to test that way. They also provide some back up cooling when the engine overheats, but we want to help you avoid the overheating in the first place.