I have a 1986 f250 4x4 and the dash mounted temperature gage reads hot--80 % of full scale. I have replaced the radiator with a double wide, replaced the sending unit and the thermostat and flushed the complete system. I refilled the cooling system with a 50/50 solution anti freeze and distilled water. The Ford house says it is the dash gage.

I have unhooked the sending unit and the gage goes to 0-cold bottom of scale. When i ground the sending unit's wire the gage goes to full scale. I have no reason to believe the truck is actually running hot. I have pulled a loaded trailer over 100 miles one way and the gage reads a consistent 80 % of full scale. I'm trying to sell the truck and this creates problems.

any ideas??

 

Have you tryed the radiator cap? I do know that the sending units eventhough they are the same do read differant, you might take that one back and try a new one. I know of a guy down the road that done this, and finaly got the one he wanted.

 

I don't know about the 86's but the many Fords have small guage voltage regulators that go bad. My temperature gauge is more sporatic than yours. I know when it is freaking out as the oil pressure gauge freaks out too. When the temp is in the middle, the oil pres. is in the middle. If the temp reads high, the oil pres. reads high. The regulator is on the back of the cluster and has connectors that look like a 9V battery.

I'm not saying that is you problem, but it has been traced to that in mine.

 

79 Indy has my opinion on this one . Had the same problem with my '78 only the temp went to the top and the oil pressure went to the bottom . A $20 used cluster fixed this once I figured what in H--L was going on .

 

What temp T-stat do you have in it?

My '79 used to run on the lower half, around the E in temp, with a 180° stat. After I changed to a 190° it runs up between the m and p.

 

If the temp gage jumps around at times check the instrument panel voltage regulator. Usually it is not grounded properly by the hold-down screw.

Instrument panel voltage regulator:

 

where's the sending unit on these? Check below for my specs. My gauge sits like it's off at all times. just quit working about a week or two ago. Hasen't been driven but 100 miles since it quit. Any ideas. Sorry about the highjack.

 

it has a new 180 as i recall.

 

Have you considered putting new gauges in the truck (Autometer, Auto Gage, Sun Pro, etc?) It detracts from the originality of the truck, I know, but having been burned on this one before (Temp gauge read normal until overflow bottle exploded in the middle of the Shirley Basin in Wyoming one cold december night, not a Ford though...), I generally make an Auto Gage 3- Gauge panel (Temp, Oil and Volts) one of my first purchases on any vehicle.

 

If you must keep your stock gauges (buy,borrow,) a bulb stile temp gauge. at least you can try to calibrate your stock one. Please note that I have not had much success with the stock gauges.