3406e underheat, thermostat stuck open.

The ONLY way it warms up is if i sit and idle with the nose out of the wind.

I am guessing on the fuel economy drop because i THINK i should have been around 6.5 mpg instead of 5.3 mpg

You say overfueling leading to cold running, presumably bad injector? but wouldnt i see (smell/taste) diesel in coolant or oil or see extra smoke out of the stacks then? None of which are symptoms im experiencing

Low heat especially down at 110 (think i managed 130 on one long but mild grade loaded to 75k gross) should result in lower fuel economy, 20% does feel drastic i agree

Saying thermostats only work at no load condition? That just doesnt stand up to any amount of logic, it may be true, it just doesnt make sense

 

So you just said yes its the tstats since ive done all that

Fuel burn may be only a 10% drop on the temp, as i was fighting a headwind and temp was rather cool, but yes i do expect lower fuel economy with an engine not up to temp

 

Yep, was a stuck thermostat.

Vaugely linked to this (reinstall) how do i get my hoses to not seep at the clamped connections? Just run a tiny bead of coolant rtv?

 

For peoples future reference

A "180" cat thermostat #248-5513
Begins opening at 180 and is fully open at 197 degrees (cat lists it in celsius, 92c, at max open status) (loaded today nearish 80k gvw, ran about 180-185, bumped up to 195 once on a moderate hill, but no long heavy pulls yet, and its been bout 45 degrees all day)

A stock 3406e thermostat (#247-7133) cat specs out a 98c stat, which begins opening at 195 degrees and is fully open at 208 degrees

Also, if replacing the ecm temp sensor, get the # 8 orb seal as well, why its not automatically included on the 108$ sensor i dont know, but i really hate it when little things like that are considered seperate.

Figured some paint was in order