I noticed the other day that my temp gauge acts erratic sometimes. I was watching it the other night on the way home and all the sudden it jumped instantaneously to about midway then slowly started dropping and jumped again until it slowly once again dropped until it got to the very bottom normal mark...and as I watched it some more it would raise up and down like it couldnt keep a temp...but i was just finding it weird for it to have an instant jump like it had been doin...what could be causing it to jump like that???

 

Short to ground on wire to sending unit or bad sending unit could be the problem.

 

Right. It could also be actual temperature changes due to a slightly sticky thermostat.

 

Another thought, that's somewhat a symptom of a thermostat installed backward although it usually wouldn't be quite that sudden. Have you changed thermostats recently?

 

I had a similar sounding problem on my 99 4.0L. Problem was the 5 year old OEM thermostat sticking. New Motorcraft thermostat has fixed her up.

Could be a problem with the temp sender or wiring as has been suggested.

Or maybe even a entrapped air bubble in the cooling system, have you had the coolant out recently????.

Just some more thoughts for pondering.

 

no i havent replaced the thermostat or taken the coolant recently...I guess Ill get a new thermostat and see if that helps anything...and if that does work just replace the sending unit

 

My '93 is having the same problem. About 2 years ago I was having a heat problem. Took out the core and found it to be pretty much blocked. I bought the truck second hand four years ago and came to realize the original owner did 0 maintenance on it. I saw the cap had an '03' written on it and assumed the coolant was changed then. That is what I do to keep track. Well, the cap was a replacement off of one out of a junk yard I found out when I asked him. I cooked out the core real good, replaced both lines, the water pump, t stat, replaced the fluid and put everything back together. I failed (duh!) to really cook the radiator good although I draimed everything down and did run water through it twice. Two years later now and I, too, notice now my gauge going up and down...actually pretty fast. My heat is good, tho. I had a boil over problem for a while where I would top off the reserve tank to the cool mark and it would boil over at times leaving a puddle under my truck shortly after I shut it off. I recently cooked out the rad good and refiled it with new fluid. My boil over problem seemed to cease, but I still have a goofy temp gauge. I think I'll tear down the t stat again and replace it. i was told sometimes if they overheat the flopper can get stuck on the shaft after that. Don't know for sure. And the posibility of a shorted sending unit and wiring is valid as well. Thanks. Some good ideas here.

 

It all depends on how "quick" the gauge jumps around. If it goes from "N" to "A" in a quick second, all fingers point to the gauge or the sending unit. Ford's gauges are notorious for doing stupid things.

For instance, my 95 had me spinning in circles. The gauge would peg on hot, yet it would run just fine and never overheated. Changed the water pump 3 times, thermostat 3 times, and it STILL pegged. But when I got in it to start it up (engine was cold BTW), I noticed the gauge was already halfway up. I then realized it was the gauge. I smacked the top of my dash, and it dropped down to cold. Every now and again, it will short out and go from "O" in Normal, to HOT. A quick smack on the dash solved the problem once again!

Now I have an aftermarket water temp gauge, which is something I would suggest. Ford's gauges never thrilled me!

Now second situation. If the gauge SLOWLY moves from point A to point B, then I'd look at the cooling system itself. Old and sticky thermostats are notorious for causing such problem.

Reguardless of the problem, it seems that it is probably a very easy fix and nothing to stress yourself out about. As long as that gauge stays in normal, you're probably fine!

 

We have a 2000 Ranger 4-banger and every once in a while the temperature guage will drop for no reason and come back up.
-Matt

 

That is likely to be a poor connection at the sending unit.

 

I will check that out. Thanks for the help.
-Matt