That about sums it up. My t-stat stuck closed last friday. Couldn't find one locally right away, so I yanked it out...I had no idea how much the t-stat controls engine temps in the winter. Anyhoo, I've only been doing the necessary driving since it's not a good idea to run the engine so cool...and I've been freezing my behind off So, thanks to Pete crossing some Cummins #'s to Case #'s, I got the t-stat kit locally. My head is one of the older ones, but did not need to be ported to fit the updated stat, FWIW. The new stat keeps the engine about 1 hash mark cooler on the gauge and, while heat was good at first, it became lackluster at best towards the end of my 30mile test run. Winter front on, flaps closed. 20 degreesF. Before, the old gal would cook me out of the cab, no problem, even on the coldest days. I'd have to run flaps open on the winter front to keep everything in check. I've recently replaced my heater core lines and flushed the core as well. So, where's my heat?!

 

Are you sure the new thermostat has the same opening temp? Don't know why the heat worked at first, must be those gremlins.

 

Could be a couple things..
1) T-stat installed wrong and not opening or opening completely
2) wrong T-stat,opening before 180*
3) low coolant
4) vacum problem preventing the heater by-pass valve from operating properly( valve located in heater hose in engine compartment)
5) corrosion in heater core broke loose when system drained and now core is blocked
6) vacum problem behind dash,not allowing gate in heater box to open properly
7) air bubble behind t-stat( common!).. if you look on the block above the t-stat housing there is a hex-key type plug, crack it and bleed off any air...where it is at, an air bubble wont move and can block the heater hose...

edit: chack numbers 3 and 7 first....
hope this helps!!!!!

 

Thanks for the suggestions!

 

I just put a genuine Cummins Part# 3802968 T-stat. Had a generic parts house one in it, with only one bleeder(or what ever they are called). The new one said 180* on it. The engine runs cooler now than it did before, and now the gauge wanders a little. The gauge was steady before.

It ran right here before.

C| |__|_|_|__| |H


Now it wanders just above the second mark.
C| |__|__|__| |H

My heater is less than impressive as well.

So is there still air in the system?

 

I don't know if mine is generic or original. It (the old one) looks like a 'normal' automotive t-stat. In the instructions, there is a pic of a similar unit and a disclaimer that says don't use one of this style with this o-ring. The new one has a solid body, for lack of a better description, with 3 bleeders. The old unit also had the bleed holes. Given my lame-o non-ic radiator, I'm happy with the lower temps and can live with the so-so heat, but I will be looking for air bubbles in the morning.

In related news, what PSI should my radiator cap be?

 

I kinda have to laugh most people in this forum fight to keep the truck cooler.I have to devise ways to keep the bloody old critter warm I sure am going to have to change the t stat(195) and put the flex a lite in, the fan free wheeling cools me of to much. I have to block 1/4 of rad off just to register heat lol. guess the new rad is working

 

While I was looking for a Cummins t-stat I went to the Case dealer and they had one that suposedly crossed, but had 3 of the bleeders. It was also very heavy duty in design.
Greg, does yours look like this?

Thats what Case showed me.

The one I got from Cummins looks just like the one in the sticky. The one I took out looks like the "aftermarket" one there.

I forgot to mention that I have about 80% of the rad blocked with corrugated board. I guess I am going to have to flush the heater core and look into cleaning the heater box.

The sticky says 15 PSI cap.

 

Greg, the design of the t-stat housing allows the stat to be installed in such a way that it blocks the "jingle-pins"( official name BTW) from opening..this normally causes an over-heat problem. the jingle pins need to be free to move.
If you used any sort of gasket maker material, it could block the stat open, preventing the engine from getting warm enough..
unlike a gasser, too cool isn't cool for our engines! they need to be "in a zone" to operate properly...
I am not familiar with the Case stats, but know that most aftermarket stats aren't up to par with the Cummins stat.
the air bubble I mentioned has happened to at least two people( me and one other) and prevented the stat from working properly and kept me from getting heat in the cab.
If you look at how the fluid runs thru the block where the t-stat housing attach's, it'll make sense to you...

 

Thats a coincidence!!! The thermostat on my 89 stuck last Friday too. I was about 50 miles from home pulling a trailer of hay home in an ice storm. Man talk about tense, 35 miles an hour with the temp gauge one click from max. I made it all the way to about 150 ft from the driveway and couldn't get up the last hill. Hope I didn't push the heat too far and crack something. I also had almost no cab heat but it had been fine?? I picked up a new thermostat from the Dodge dealer today...80 bucks (ouch) and hope to get it installed in the next couple of days.

 

yup, that's the one. It's got a really deep shoulder on the other side, making it impossible to install it backwards. Plus, I followed the pictures on the install manual, just to be sure The one that came out looks like Jim's in the sticky, though it had 3 weep holes, not 1. The new stat also has 3 weepers.

 

Oooh, just found this page---here's what mine looks like, only not as broken:


http://www.mvdirona.com/TechnicalArt...ateFailure.htm

 

Well, I think the overheat last friday cost me a headgasketI'm trying not to get ahead of myself, but the coolant in the overflow can was pretty black...and I'm low on coolant after burping the system and re-filling this morning. No coolant in the oil....I was really hoping to hold out for a 7mm head before I went after this mess I'll have a look in the morning when I'm less disgusted, hehe

 

these symptoms sound like what mine was doing. came home one day and the temp gauge was one hash mark from the max. so i put a replacement thermostat in from napa. then when i would drive it was weird when the truck initially warmed up it would have heat then all of a sudden the heat would stop and it wouldn't blow warm for the rest of the trip. but the temp gauge now read colder then before. about a week or two later it started bubbling threw the coolant resivour. so i pulled the head, it was the head gasket. i believe it was the #5 cylinder was putting air in the coolant system. it wasn't a total failure of the gasket just enough to allow it to put air in the cooling system. during all this the truck didn't change the way it ran it was just the heat would act up. so i put a new gasket in and everything was well again.

 

I have added AF three times since I put the T-stat in. The only reason I changed it was because it took a long time to warm up. The new one helped that. I even bled it with the plug right above the t-stat today. This made room for a little more (1 pint approx) AF. The temp gauge wanders a little less now. Are these things really touchy with air in the system, or what? I hope the HG didn't coincidentaly sp? blow.