Vehicle: 1996 Tahoe, 2 door, 4x4, NV4500 transmission
1993 Cummins engine

When I'm driving, the coolant temperature fluctuates from about 180 to 215 on the gauge. It'll go to 215 then about 30 seconds later it'll drop slowly back down to 180 then it'll slowly go back up 30 seconds later to 215. It just keeps cycling back and forth. My other vehicle doesn't do this so what's wrong with it? And yes, the radiator is full of coolant.

 

Is an aftermarket guage or a factory guage?

 

Just your thermostat opening and closing.

 

^This^

With my mess, it's more pronounced with cold weather. Not a problem.

 

Consider yourself lucky, it's a properly working thermostat, I think mine is stuck open. Or it opens and stays open; no in-between


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Sounds fairly common for the 12v. Mine does the same. You can get a tstat from cummins that holds a little more steady but takes forever to warm up