My thermostat acts like yours all the time (swinging between the second mark and below the first). I have considered replacing the T-stat, but I've heard some thermostats are just swingers

 

Thanks, that makes me feel better about it.

I thought I read an old post where someone said the upper (2nd) mark on their factory gauge equaled about 260* on their aftermarket one. That sounds way too high and it seems like that 2nd mark shouldn't represent such a high number.

 

I installed the factory cummings t-state and it hold steady all the time......unless i'm pulling a long hill and when i take my foot out of it, it will slowly return to normal!

 

I installed an industrial autometer, mechanical temperature gauge and the 1st tick mark where it runs normal is about 160deg, needle pointing straight down is about 180deg, and the 2nd tick mark is about 200deg. So I would say that running at the 2nd tick mark is just fine but any more I would slow down. The fan also kicks in right at 180deg, on mine anyways.

Aaron

 

Thanks a bunch, Aaron!!

Those numbers are exactly what I was looking for. Looks like the 2nd mark is right about where it should be and maybe I can get away with not installing a coolant temp gauge now.

Everyone says to use the 1/2" plug below the T-stat housing on the head when installing a temp probe. I can not find this plug for the life of me. I see what looks like a 1/2" port where people are saying to look, but that seems to be used for the tranny heat exchanger. Is that port only open on 5spd models? Does anyone have a pic of the plug and maybe even a pic of their probe mounted in this port?

 

I put my probe in the 1/2" hole in the top of the t-stat housing right next to where the heater line goes in. I'm thinking about moving it to the side though.

 

My probe wouldn't even come close to fitting in the top of the T-stat housing. It seemed to bottom out on the T-stat (I guess?) itself. I'm dying to know if only the 5spds have that other 1/2" port available? I'm also dying for a pic of it on someones rig.

 

I had to get a different adapter from the hardware store to space it out enough. I didn't know about the one on the side at the time. After I installed it I saw the port on the side but I can't remember exactly where it is right now.

 

Mine too, and it's a genuine updated Cummins unit.

 

Get a Japanese Motorcycle wrench. That is what some of us call an impact driver. I got mine from Sears but there are other brands out there. They come with different screw bit drivers that go in the socket on the drive end. You find one that best fits the slot and gently but firmly rap it with a small hammer while trying to turn the screw and the screw will either break loose or off. I have taken off some several stuborn screws in this manner with good results. Once you own one you will wonder how you ever got along without it.
The reason for the one flat head screw is strictly economics. The trucks with the standard trannys don't have socket head cap screws because there isn,t a throttle positon sensor. They didn't need longer screws. If the truth were known it is most likely a Chrystler mod.