I HAVE A BMW 3 SERIES, WHEN I TURN ON BLOWERS TEMPERATURE SHOOTS UP TO RED, DO YOU KNOW WHAT IT CAN BE

Thermo stat either gone on on its way out.. if it does shoot to red when idle then def thermo stat

Check the water level in the radiator

The car is fine every other time & only runs hot when the blower is on? First see if u have two electric fans attached to the back of the radiator. On comes on when the car is hot, one if u turn on the A/C. Since some cars heaters & defrosters also kick on the A/C unit, check to see if the second fan comes on. Actually, check to make sure any of them come on. Raise the hood & run the car until it is warm; at some point these fans have to start running. If they dont the switch or fan motor has gone bad. If fans r working & it only gets hot when the blower is on u could have a short in the sender unit/bad thermostat/radiator/waterpump in order of cost. If the car has high mileage get a flush. However it is unusual for the heat to shoot up because of activating the blower.

you temputure gauge is grounding off replace the switch if the car is not overheating