My 2500 has over 223K and was just wondering about changing out the T stat. Changed coolant at 100K IAW owners manual. I've notice lately the truck warms up rather quickly and climbs above the normal range then drops back down in the cooler weather. Wondering if the T stat is sticking. Since I like to practice preventative maintenance I'm leaning toward changing it out. Anyone else with similar mileage experience this?

My '06 has 522371 miles on it. NEVER had the valve cover off of it---still has the OEM thermostat, If I were you, I'd change the thermostat. I think I have the best 5.9 ever built.

You may be right, that's a ton of miles

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I've had the valves adjusted twice. 100k and 200k. At 220K I took it in and had two injector lines replaced. While they were at it I wanted the PCV changed out. Apparently my truck was a late run and it has a newer valve cover with a PCV built in. In order to change it you have to change the entire valve cover. Crazy!! Everything looked clean so we buttoned her up and called it good.

The rubber seal on the thermostat is bad for swelling and hanging the thermostat open or closed. Easy to replace. Spend the money for a Mopar one if you decide to do it. On another note, given the mileage you may consider changing the water pump since you will be draining the coolant for the thermostat change. They tend to go out all of the sudden without much warning on these trucks. Just good preventative maintenance IMHO.

That was changed out last summer. Had the water pump, AC compressor and serpentine belt tensioner changed out. I usually go to Cummins for parts like that.

My '92 has about half that mileage on it.

Soooo.., what's your point?

I guess there wasn't no grass growing under that one.

cooler weather in the desert makes you notice how poorly your t-stat is working. Been more than a couple occasions where I noted my 01 was running a little warmer towing during the summer, but it wasn't until coasting down a long grade in cooler weather that I'd watch the temp gauge plummet. T-stat time. Think I'm on my third in my 01.

Went by the Cummins shop and picked up a T stat. Just finished changing out. Now, temp goes to 185 and stays there. It's currently in the low 60s right now so I'll have to wait and see when I do a tow up to the NW in several weeks.

My guess is the higher temps while towing will come down.

I think you'll be OK.

Drove about 80 miles today on the freeway in traffic. The temps held steady 185 to 191. Tranny temps were down 10 degrees below that. I think the T stat change made a differance.