Hi all,
temp gauge fluctuation fix was just a new radiator cap.
Before I put the new cap on I did also remove the old cap first while engine was cold and run it until warmed up which i read could possibly let air out of the system? Not sure it’s true but it appeared harmless enough. I added some premix antifreeze because it was low. It ran for a while and the temp gauge stayed steady at the midway point.
the next step was to put the new cap on and let it run a bit more monitoring the gauge all was fine. I continued to let it run until my wife said what are you waiting for it to do, run out of gas?
no more fluctuations. All fixed.

ALSO IF YOU READ THIS FAR and you know what size bolts go to the thermostat housing on the 2000 4.0
apparently I lost one? or it wasn’t there not sure it has 280,000 miles on it maybe some other diy’er hack lost it COULD YOU TELL ME WHAT I CAN ORDER TO PUT A THIRD ONE BACK IN. THANK YOU
I did do the thermostat first. I wish I was smart enough to start with the radiator cap.
I have a 2000 Ford Ranger XLT pawn shop special I bought as a starter farm truck. My temperature gauge was fluctuating pretty much non stop from midway to max putting the check engine light on and the AC was not cooling.
the overflow had boiling antifreeze in it when I checked it.

 

Overflow tank was Bubbling not boiling, just FYI
That means air is in the top of the radiator