Installed new cummins thermostat...
 

I just put in a new thermostat from cummins (part # 3928499), and I'm getting huge temperature fluctuations. I read that this was a problem for unloaded trucks because of the large radiator, but I thought the new thermostats from cummins would fix the problem?

When the truck is warmed up and I'm cruising down the hi-way the gauge jumps from the halfway mark down to under a quarter and then climbs back up and repeats. I drive most of the time unloaded or very lightly loaded so I would like to fix this problem if possible:argh:

You may have gotten a bad t-stat, or there is some air still in the system.

Ok thanks, what's the best way to bleed the cooling system on these trucks? Might as well try that first before I try to get warranty on the thermostat:argh::dang:

Drain about one gallon from the radiator. Remove the upper hose and neck together, then pull the t-stat out. Pour coolant into the block where the t-stat sits until the block is full. Tighten the neck back down, then fill the radiator, squeezing the upper hose until you purge all the air, and the radiator is completely full of coolant. Also, be sure the recovery tank is at or just above the max mark. Drive the truck and see if the problem still persists. If it does, need to get a new t-stat.

i dont think you necessarily have any problems the thermostats are notorious for doing that from cummins. mine did the same thing. replaced thermostat with 4 different ones and same thing every time. i just gave up and dealt with it

its normal!!

I believe so. You are seeing the actual temp. Be thankful - the later trucks have a dummy guage.

I read that it was normal, but I also read that it had been fixed by an updated thermostat. I guess I just don't like the thought of the engine being heated and cooled so drastically all the time. But I do like having a real gauge:tu::rocking:

Quote from geno's garage:

So according to this cummins sold me the "old" thermostat, I guess it's my fault for not asking for the new part number specifically, I assumed they didn't sell the old one anymore :argh::td:. Has anyone tried the "new" thermostat, how does it work? I would think it just opens slower?

The temp changes used to drive me crazy to the point of watching the guage paranoid something was wrong but after 2 t stats and a full coolant flush ive learned to live with it.

Haven't had an issue since I changed over to a NAPA heavy duty.

My truck never did this untill I installed a new tstat from NAPA. Nothing was wrong with the old one but the seal was leakin so I figured as long as I had it apart I'd stick a new stat in it. Now I can watch the guage run up to 190 then drop down to about 140. Freaked me out at first but it dosn't go over 190 so I got used to it. :c:

No Heat
 

I have a 1996 Dodge ram 2500 and i have replaced the thermastat radiator and also had a system flush and i still have no heat can anyone help me out please

Theres a sensor on the back of the motor that controls your gauge sometimes they go bad or get loose and that will cause your temp gauge to act up.

I have a 97 & it does the same thing since it hit 68,000 mi. Now has 198,000+. Still drives me nuts & like others, I watch it all the time. I may try the updated t-stat

Mine only does it in the winter. If it's really cold, well below freezing, and I don't go off the highway, it will only do it once. Warm up to about 195 on the gauge, then the Tstat opens and it plunges to about 150 and stays there. If I'm doing mixed driving it's up and down like everyone else. If I let it idle too long in the winter it stops warming up and starts cooling off, eventually it cools off almost completely. My heat has never been good, it's only ever warm at best. New core, system is full. It's always been like this as far as I know, I've put over 200K on it, as far as I know the first 125K was no different. Just an old horse doin' what it's always done like these old horses did. I've heard rumors that they aren't all like this, but I've never had a mechanic under it who could find anything wrong Attachment 34503

In the winter .. put some cardboard in front of your radiator .. . I have my CAC and all covered up ... right behind the grill and such .. my heat is awesome .. runs me out .. :c:

My truck does the exact same thing during cold temps, and I have the new part# tstat. Sounds silly but I jack the front end of my truck up real high to hurl my system. It's always worked well for me. .