Dash Temp Gauge Suddenly Stops Working after 5 miles with heat blast on my foot

[TravelNomad]

Need help/advice please. Have 97 Explorer Sport SOHC 4L 6 cyl 4WD w/ 275k miles on it! Sat in hot sun @ border crossing for 2 hours w/ car on, windows down, no AC used. Then crossed to freeway going 65 mph, suddenly felt blast of heat on my gas pedal foot; lasted 5 miles. No heater was on, No smoke, no noise, no driving problems happened. But my Temp gauge (usually at half way) dropped below C/It never moved again. Heat Blast stopped for the next 7 miles. I am scared to move the vehicle- could it be intermittent fan problems or thermostat? I know zero about cars; advice on how to diagnose the problem please. THANKS

 

[2000StreetRod]

check the coolant

I suggest that you check the coolant level in the reservoir and also in the radiator after the engine cools. The symptoms of a significant coolant loss are first overheating and then low temperature when there is no longer enough coolant to contact the temperature sensor.

 

[TravelNomad]

Oh, thanks much for the reply. This situation happened yesterday; today, I did add water to the overflow (reserve) and some anti-freeze and water to the radiator. The overflow was empty...don't know how low the radiator was. Not sure when my fan is suppose to come on (someone suggested it might be acting up so test it)...but was afraid to go out and about to test it and blow a gasket. Guess I might have to do that then. Don't know how to test the thermostat. After I filled the res. and radiator yesterday I drove it 6 blocks. Parked it for an hour and drove back 6 blocks. No heat coming on foot but the temp gauge never moved and usually it goes to near halfway fairly quickly and stays there. Guess that is what is troubling me most - old car, lots of miles but not an abused car.