ECTs High -- Thermostat

[jd4010]

2004 F350
New EGR and Oil coolers - about 500 miles ago along with new fluids (done at dealership)
Mileage - 51k

Went camping this past weekend...hauling the 5er (16k #s). Temp outside was around the low 70s to upper 60s and on the haul to the grounds, ECTs ran about 189 to 190 (give or take some as we hit some grades, etc). EOTs ran close with an 8 to 10ish differential. This is what the truck runs normally hauling this rig....sometime goes up when hitting grades but always comes back down.

On the way home, the outside temps were about mid to upper 70s but I noticed the ECTs were running around 215 constantly making the EOTs around 220 ish. The engine fan would occassionally kick in hard too.

When we got home, as customary, I let the truck idle for about 5 minutes and usually during this time, the EOTs fall to upper 180s and EOTs to around low 190s. But this time, the EOTs never came down....stayed at 216 as did the EOTs.

Shut the truck off, let it sit 15 minutes, fired it back up and the EOTs were down in the low 200s. This time, shut it off for an extended period of time, parked the camper and went (empty - no camper) to get fuel. EOTs once again were 189 to 190 and EOTs 195.

Is is possible that the thermostat is getting stuck and not fully opening causing it to get and stay in those 200+ range?

[Lilpooh]

What year truck, and list any mods.

[bfrank81]

I just got back from trailer 2 motorcycles in an enclosed trailer (much less weight than you) from DE to FL and back. My CST never showed that high even when I really got on it just to try.

When was the last time you flushed your coolant?

[Dave]

Go through your post and fix it. So we know whats what.

But if the temps remained within 15 degrees its not an issue. How heavy is the camper

[jd4010]

Originally Posted by Dave

Go through your post and fix it. So we know whats what.

But if the temps remained within 15 degrees its not an issue. How heavy is the camper

I updated the original post.

However....the concern here isn't the hitting of the 215 EOTs but rather the fact that they didn't come down when idling when we got home. Usually after a long haul we let it idle to let the EOTs and ECTs go down (instead of shutting it off cold turkey). This time, the EOTs and ECTs didn't go down...almost as if the thermostat was stuck closed somewhat.

Some additional info....when it was idling and staying at 215 ECT, I checked the degaus bottle and the fluid level was at the min level. When I finally decided to shut it down after seeing the temps weren't moving, the coolant level in the degaus shot up almost instantly to the max level. But know....that once the truck cools, the level in the degaus bottle is at the min line. Hence I'm thinking the thermostat stuck closed (or partially opened) and when the truck was shut off, it opened full.