Another method is to touch and firmly hold a digital cooking thermometer to the thermostat housing of the engine — generally where the upper radiator hose connects to the engine. An analog or needle-type gauge will also work, but it needs to be held there for a longer time. An infrared, noncontact temperature gun is another, very convenient way to check engine, brake and other automotive system temperatures. Point the gun at the thermostat housing. Normal engine operating temperature is between 190 and 200 degrees Fahrenheit, and most electric cooling fans engage at around 220-235 degrees.
Did your “check engine” light illuminate soon after the temperature gauge irregularity? If the vehicle uses a shared engine coolant temperature, or ECT, sensor, this would be likely, as an extremely low or high reading can affect emissions compliance.
Without knowing the vehicle make and model, it’s difficult to say where the fault may lie. You may have a faulty ECT sensor, circuit fault, or instrument panel malfunction. I’d recommend checking the coolant level and gauge operation one more time before driving again. If the gauge continues to read high temperatures with the engine stone-cold, it’s clearly wrong. Then I’d get it to a shop as soon as possible. You don’t want to drive without a functioning temperature gauge, especially as you aren’t able to validate actual temperature.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at firstname.lastname@example.org; he cannot make personal replies. Distributed by MCT Information Services.