3406e underheat, thermostat stuck open.

Less than ideal, thermostat(s) stuck open (i think)

Good news, i know my radiator cooling capacity is about 80 degrees over ambient just driving

Coolant temp top right (sensor in tstat housing)
The coolant guage is the second most accurate one in the truck, it is DEAD on, i did verify that with heat gun

Any other guesses? No oil in coolant or the other way around, still pressurized cap, no real power loss (some probably from incomplete combustion, fuel mileage dipped 20% but no power drop that i can properly feel)

Other possibilities?

 

Its correct

That doesnt make sense, removing thermostats made engine temp go UP? Also its been wet and 40 degrees, if yours happened during summer, + 50 degrees seems right for max temp

1. Oil pressure sensor (for gauge) installed at back of oil gallery, this ought to give a little lower reading than at the front (old sensor was apprently broken off in there when engine was swapped, cat didnt fix it on rebuild)
2. Approximately 400k (since rebuild in 2014

 

(Since underheat condition, total 600 miles, home and get to tear into it now)

Was curious what the hive mind thought of diagnosis

 

The coolant guage is the second most accurate one in the truck, it is DEAD on, i did verify that as well as freezing in the cab the past day. I really dont need more people telling me to check with the heat gun which is literally the second thing i did, as such i guess i need to add that to the top post. (Sorry, im just miffed that the assumption is immediately that didnt bother to check the obvious first)

Ecm coolant, i assume you mean as in via software to check the ecm coolant temp reading? Because the ecm is fuel cooled on the 40 pin. Also how is that relevant? The coolant temp IS 110 max under load, how would the ecm drop temp 85 degrees outside of just turning off?