water gauge show wrong tempherature

i think my water gauge show the wrong themperature and also the needle jumps about a mm when i rev the engine, the fans go on in about 98c and go of 93c on the gauge, my theromstat in radiator is a 80-85, someone had the same symtoms that the gauge jumps some and show wrong readings?

 

Is it only the water temperature gauge needle that "jumps", or do the oil pressure and oil temperature gauge needles also jump?

 

Does the gauge(s) jump when head lights turned on and off?

 

i dont think the other gauges jump, but i need to check that, i have a new modern spade fuse holder and solid 12v thrue all system.

 

need to check that.

 

Dodgy electrical grounds can cause fluctuating readings. You can get a good check re indicated temps with an infrared temp gun checking the temp at the thermostat box and comparing it with the gauge. It's most important that the gauge respond consistently as the temp goes up/down, it's not too important whether it shows the correct temp. If the gauge is responding consistently, you can mentally note the correct operating range based on the IR gun and as long as the needle stays with that range, you know you are OK.

It's worth noting that thermostat temp rating is the point at which the T-stat BEGINS to open.

 

Today i found the problem with jumping needle, the + on battery was lose, cleaned everything up and tighten it, then the water them needle stop jumping, i also checked watertemp with a laser gun, when gauge show 94 celsius the engine is 86c and hottest temp today was on gauge 98c and then 90c on engine, i hope the problem is the temp sensor and not the gauge., now i need to find the correct tempsensor for my Euro 1979 carburator GTB

 

If you do a search on the "104628" part number, you'll get many threads about it -- it's used on many F models (but it's rather inexpensive so just replacing it is easier than making it a science project ).

 

Now the sensor is on its way.=), do you know if it is possible to change the sensor without removing carburators?

 

It's been too many decades since I fiddled around under the airbox of a carb 308 to really know/remember. My guess would be that it's not super-difficult (since we don't seem to get threads complaining about it ), but, hopefully, some carb 308 FChatters who have done this replacement recently can comment.

 

With the oil filter off it would be easy to remove, you may even get away with leaving the air cleaner in place.

 

Sweet - Sometimes you get lucky! (Don't get me started on evap coils - not for an F-car)

 

Put lots of rag around it as water may gush out when you remove the sensor or drain some before removing the sensor.