Originally Posted by
Anthony McGrory
Hi,
Just bought a Sierra.
my temperature gauge moves up and down as I drive. Reads up by the N if I’m idling and then goes straight down to the M when I’m driving. The needle moves very fast. I’ve never seen a temp gauge move so erratically.
what is strange is that even when I start the car from cold the temperature gauge goes straight up and moves up and down as I drive?
any suggestions on if this is a sensor problem and how to fix?
Hi, the cause is due to low voltage of the whole car electrical system (note that the temp gauge sensor is just a piece of variable resistor). Temp gauge display is base on the voltage readings after the sensor. Your alternator output could be weak (due to age). If you had the alternator replaced, then the cause can default to the wire that goes from the alternator to the battery. Consider replacing that so your car will restore full working voltage like when it left the factory. This will give more accurate readings not only to the Temp gauge but also other signaling of the car.