temp gauge swinging

[shackwrrr]

Driving down the road my temp gauge constantly rises to the 2/3rds mark then falls to half. Never stops and does it at any speed. Truck has new radiator and coolant is full. Gauge or sender? Possibly a thermostat?

[matthewh]

Does it do this more when its cold out? Could just be the thermostat opening and closing. If I don't have my grille cover on, or the radiator partially blocked when the cold hits, my temp gauge does the same thing.

[shackwrrr]

I haven't driven it yet in temps higher than 50 yet. Just new truck anxiety. Trying to figure out all the "normal" quirks.

[Remps]

My guess is a cheap t stat was used. The parts store t stats tend to do that. I'd replace it with a genuine cummins t stat.

[RCCUMMINS89]

Mine did that when my thermostat was installed upside down. There is a few holes on the thermostat, they need to be up when it is put in

[MARF75]

It's a cummins, they do that. The 3 first gens I've owned all did it.
I did some research on this and some of the second genners have drilled a tiny hole or 2 in the rim of the t stat to allow more water to flow thru when the t stat is closed.
What I got out of it is the cooling system works so well that when the stat opens it cools enough to shut the stat then it heats backup, stat opens and over and over and over and that's what you are seeing on your gauge.

[shackwrrr]

Thanks for the replies, I'll get an oem Thermostat at work (I work at a dodge dealership). I'll try it as is and if it still does it I'll try putting a hole in it. I did this on my turbo van with great success.