fluctuating water temp

[BubbaTC]

I had this prob when I first got the truck a month ago. I had to replace the radiator so I also replaced the WP and converted to electric fan. I also replaced all the hoses and thermostat. I still have the same prob. ive made sure that there is no air in the system. Its fluctuating between 180-220. I installed aftermarket gauges. It hasn't overheated on me but its kinda a little weird to me.

 

[RonD]

My '94 4.0l had the same issue, it would go from under 1/2 on the temp gauge then up above 1/2 with no change in engine RPM or engine load.
Just randomly go up and down, never overheated, I too replaced several things.

Turned out to be the heater core, go figure.
On my '94 the heater core is the cooling system by-pass, if coolant flow is limited then temp fluctuates.
Heater core was $28 and 4 screws to remove, took 20min.
Benefit is heater is way HOT now, it was always warm, just real HOT now.

 

[BubbaTC]

hmm I don't have any probs with heat, its plenty hot when I turn it up