Engine Temperature Gauge Problem

[Elmobile]

I have been having problems recently with my 1988 Bronco II. It doesn't matter what the outside condtions are when this happens. The temperature gauge will read higher than normal and will max completly out to hot (overheat) on multiple occasions during short drives (less than 20 minutes or 15 miles). It will even do this several times idiling in a parking lot when the outside temperature is below freezing. The vehicle doesn't seem to be overheating, no expansion into the coolant resevoir etc, and the engine didn't blow when I ran it anyway for a minute or two in the red. The gauge will max out, then a second or two later will return to relatively normal. I took it to the mechanic, who put in a brand new radiator, water pump, power steering pump, and hoses. I have flushed the coolant and have not observed any bubbles, contaminants, or leaks anywhere on multiple occasions. I have gone through three thermostats and I now use a 160 degree thermostat. I have replaced the temperature sending unit sensor that reads the temperature multiple times. I have completly run out of ideas and things to replace short of the gauge itself. This vehicle basically has a whole new cooling system and I have put well over $1,000 into fixing this problem. I recently bypassed the entire temperature gauge system to find out if it is the engine or if its the gauge. The mechanical gauge I used showed no abnormalities and consistanly stayed at 160 degrees like the thermostate was suposed keep it at. I think the gauge is the problem. However, no one carries a replacement temperature gauge anymore. Is there anyone who can tell me if it could be something else or if there is a way to test this electrical gauge "electronically", measuring the electrical resistance maybe. If so how many ohms is it supposed to read. I would really appreciate if anyone could help me with this extremly expensive and irritating problem.

 

[dzk007]

You have a bad wire to the sensor unit on the engine. The wire is either grounding (my hunch) or creating an incomplete connection (which I believe would drop the gauge to the cold end).
Somewhere between the dash gage and the sensor you have a problem. Chase the wire back to the firewall by the noted color and thouroughly check it for ANY abnormalities.

 

[Elmobile]

Thank You, your a life saver.