Temp Gauge Stuck on Hot

F

Fortunateson

Well-known member
Now this question applieseadle to a '87 Ford F-250 so if it's too new of a vehicle let me know...

The problem is in the title, the truck overheated once which pegged the needle and it hasn't ever dropped back down even with the battery disconnected. Any ideas guys? I've replaced the correct temp sensor and no luck...
 
Think the last year for the old style gauges was 86, your 87 should be the stepper motor type. Maybe a little smack on the side of the dash close to gauge will free it up. That would be my first move, if that doesn't work I would try another gauge. Need to make sure the temp sender wire hasn't grounded on something.
 
Okay I'll try that. Up here the '87s were a combo of '86 and '87 it seems. My 351 is carbureted but it seems there were injected ones as well so getting info I sometimes divert to '86. The Gauge I believe can't be separated and I want to keep my speed/odometer.
 
I believe you are correct. I don't have a manual that covers 87, there are some tutorials on you tube.
 
Fortunateson said:
... the truck overheated once which pegged the needle and it hasn't ever dropped back down even with the battery disconnected. ...
Click to expand...
5851a said:
... Maybe a little smack on the side of the dash close to gauge will free it up. ...
Click to expand...
If the needle normally rests at Cold but is now stuck at Hot even with the battery disconnected, my first guess is the needle over-traveled itself and just got slightly stuck on something.
Or... the little coil for the needle mechanism also got too hot and may have warped itself out of shape, a slightly more permanent problem.
 
Kind of what I was thinking. Perhaps the needle pegged itself and it was pegged too long and damaged the spring. Can those parts be transferred from one gauge cluster to another?
 
1987 may predate computer involvement but I don't have any info on them. If it is a sender to indicator circuit only then I would suspect the indicator and especially when it is isolated from electrical power. If an engine computer is involve then the indicator would have to be tested to see if it works. It should go to dead cold when the indicator unit is disconnected from the computer.
 
[FONT=&quot]I don't know how important originality is in this case, but even on my mostly original old Fords I use decent quality aftermarket mechanical temp gauges. You can mount them under dash without much permanent alteration. What a wonderful thing it is to not have your temperature readings be mysterious! And you can see how much the temp goes up after the truck is shut off. [/FONT]

[FONT=&quot]To remove even more of the mystery, you can boil the sensor of the mech gauge in water before installation to see how accurate it is. Water boils at 212 deg. F so ideally your gauge should read close to that at the moment boiling starts, but even if it doesn't, you know how far you're off and you can easily perform the mental calculations when the truck is in use. One of my gauges reads 10 deg. cool, another 4 deg. cool and another is spot on. [/FONT]
 
The boiling point of water varies with pressure altitude so make sure you figure that in when testing with this method. I just use one of the infrared thermometers when I test temperature reading instruments. They aren't very expensive and can be used on anything from engine blocks to tires.
 
I have an 81 F250...mine was stuck for awhile while a spider was in there. It doesn't take much to bind it up so id suggest getting in there and gently moving it to free it. Also, depending on your location, you local junkyard may have many many of interchangeable parts.
 
Rotorwrench is correct about elevation, and especially the temp sensor tools, which are a great help. The advantage to boiling before installation is that if the sensor and gauge are too far off from the factory to be helpful, you can return the item uninstalled. Some stores/vendors are picky about that.
 
Well I installed a replacement gauge cluster for the wrecking yard/"auto recycler" and the temp gauge is behaving itself. Noticed two things though... even though the engine has the correct amount of oil the needle just enters th normal section and there was a lightbulb in the replacement cluster that had a resistor incorporated into the base. Any ideas on either of these occurrences?
 
Fortunateson said:
... even though the engine has the correct amount of oil the needle just enters th normal section and there was a lightbulb in the replacement cluster that had a resistor incorporated into the base. ...
Click to expand...
Isn't the "Oil" gauge for pressure, not quantity?
IF the truck has an oil level indicator it's often a light.
 
Sometime in the 80's Ford put a resistor in the circuit for the oil pressure gauge. The gauge is not really a gauge. It functions the way a red light works. If you have any pressure at all the gauge will register in the normal range. The resistor on the bulb, I'm not sure on that one but Ford did use a resistor wire in the alternator light circuit.
 
It registers in the normal range but just barely. I wonder if a new sending unit/sensor/switch might get the needle in the centre? That bulb with a resistor is weird but someone must know.
 
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