[Ford Man]

Knowing a little bit about cars myself I also think it's the sensor instead of the SG II. I know many cars have two sensors for the temperature, one that sends the signal to the ECU and another one that sends the signal to the dash mounted gauge. If the one sending the signal to the ECU is bad and the sensor for the gauge is good that would explain the SG II getting crazy readings while the temperature gauge reads correctly. I'd suggest checking to see if your car does indeed have both sensors. If it does replace the sensor that sends the signal to the ECU. I keep the SG hooked up continuously on my '97 Escort and have for probably about 2 years and never have had a problem. The SG in itself has nothing to do with the readings it receives all it's information comes directly from the ECU and the sensors that supply the information to the ECU.