It's winter, and I've got almost no heat! Vehicle is a 97 F-350 PSD, 177 K miles, I've only put about 400 miles on since I got it. My first diesel, so I'm not sure what is "normal".

I've driven a few stints long enough that it should have warmed up; temperatures in mid-40s, highway distances of 50 to 80 miles, 50 to 65 mph, no load. Every time, temperature ssslllloooowllllly rises to just above the low-normal line on the gauge (not even to the "N" in normal) and stays there. Temperature rise time is much slower than any gasser I've driven. Heater air is barely warm, about what I expected from my other vehicles after 2 minutes of idling in similar temperatures.

In 30 degrees, I plugged the block heater in for about 45 minutes, then started it and left it to idle for 15~20 minutes to keep batteries charged; gauge moved but didn't even make it to the normal range.

When I turned it off, both heater hoses were lukewarm to bare hand, and upper radiator hose was only a little warmer than the outside air.

The heater controls appear to work OK. Fan works, selector switch makes air come out in the right places and activates the AC (which is colder than the outside air), but "heat" or "defrost" yield only tepid air. The temperature **** works the blend door actuator on the plenum, and it feels like the door itself is moving.

The slow warm up, stabilization temperature at the bottom of the "normal" range, and only slightly warm heater air and hoses suggests a thermostat stuck partially open. But I don't know where a PSD should operate on the temperature gauge and how long they take to warm up.

Finally, the questions: Where do your trucks operate on the temperature gauge? How long before the temp stabilizes in mild winter conditions? Does stuck thermostat sound about right, or should I be looking at something else?

Thanks for the help!

My wise thought for the day: Repair is usually easy- it's the diagnosis that's the difficult part!

 

Sounds like you already diagnosed the problem as a stuck thermostat. Mine also stuck open so I bought a NAPA unit. Although the NAPA was of correct dimensions, it was the wrong one and I finally had to go to Navistar for the right one.

The Navistar thermostat has a check valve off to one side to bleed the air out of the block and the NAPA one didn't have that.


PS drop one them little bolts down into the intake valley and easy goes right out the window

One more thing, don't pry very hard on the radiator hose tube while removing it, it looks pretty thin down at the bottom.

 

Thanks for the feedback. It gives me confidence that I'm on the right track. I guess I can put the dash back together- I pulled some pieces to trace the blend door control cables. I'm planning to change most of the fluids (coolant, oil, differntials, transfer case; NOT auto transmission since it's a new Jasper)when I get access to my buddy's lift (9 Klb) and will do the thermostat when the radiator's drained.

I will make sure that I have my claw & magnet pickup tools along in case I drop anything into the valley. That tip sounds like one that was discovered the hard way.

I'm guessing that when fixed, I should see temps in the middle 1/3 of the gauge.

No heat would be a major problem for one intended use- shuttle vehicle for whitewater paddling. Think a bunch of cold, wet, muddy paddlers back in the mountain valleys of West Virginia during early spring rains.