So, I've been fighting heater issues for some time now. I've lifted the front end and bled the core (several times), blah blah blah. Sitting in the driveway I've got little over 100f with the fan (and heat) on high. 100 times better than it was. Time for a test run. COLD COLD COLD. I'm out for about an hour driving around in town, 25-30 mph and the truck never warms up.

I should have checked the thermostat in July, but Nooooo, I gotta wait till it's 36 outside. I didn't want to check it, just replaced last march, should have been fine. But it's the only thing that would prevent the engine from reaching operation temps. So I pull the hose and the cover off and what do you know...valve is wide open. Looking at the underside of the thermostat I can see two brass clip thingies next to the support posts.

Here's the riddle. Why in the hell would a thermostat have brass clips that engaged when the thermostat opens, but never disengage? Went out and got a new thermostat and another tube of sealant and stuck it in last night. I can't find an example of this thermostat online, maybe I'll post a pic today/tomorrow and someone maybe has an answer.

 

Cheap thermostat maybe. The Q is is it better now with the new one?

 

that is a failsafe thermostat. when the truck overheats the thermostat will lock open to prevent damage from the engine being too hot. 13$ for a new failsafe is better than a couple grand for a new engine.

 

I had a fail safe t'stat that stuck open also.
The engine never overheated but when it failed it went open.
I was under the impression that if the t'stat screwed up it was designed to go wide open.

 

Seems like these Failsafe thermostats fail more than a regular thermostat.

 

i stuck a new t-stat in a few monthes ago and i still have very little heat

 

Failsafe huh? I guess there is the possibility that it stuck open on the WI to SD trip in July. Temps never once reached 210 to my knowledge (I'm kind of paranoid about high temps, stranded a few times in HS). Lost an A/C clutch, but that's another issue. Installed the new thermostat, different store, different open temp. Failsafe was 192, new is 195. Electric fan set to come on when the rad hits 190'ish. Cab heater is blowing on high about 99f when the truck is warmed up. I don't know if that is high, low, or just right. I don't hear a gurgle in the H core when revved, but will check again tomorrow.

 

According to my Service Manual, at 60* ambient air temp the heat coming out of the floor vents should be around 140*.

 

It would seem I'm a tad on the low side. Before replacing the thermostat I was pushing 110-115 from the core with an engine temp of 190(ish). Time for another bleeding of the core...what a pain in the ****!

 

I never bleed mine after i put a new stat in,looks like i might have to do that