Make sure you have the correct thermostat in there, if it is set too high you will get that bouncing.
The thermostat is set to open at a certain temperature and allow the coolant to exchange with what is in the radiator. Under normal conditions you will notice a rise and fall of the temp gage as the coolant reaches max temp then lowers after the exchange.
An overly sensitive sensor or an aftermarket gage set up will exaggerate it.
I would not worry too much since it is a good indication that your cooling system is working well, the coolant in the radiator certainly seems to be cooling down enough to cause a big swing in temp.
Check on that thermostat though as it may be letting the coolant get too hot before releasing it.
Check the fan thermostat.
It could be the radiator is clogged. The thermostat could be bad (prevents the coolant from circulating from radiator to engine block)
Low coolant, plugged radiator, inoperative fan, stuck thermostat.
Lack of coolant in the radiator. Fan not working. Not enough oil.
The coolant could have frozen in the radiator. If that happens the coolant in the engine will just get hotter. It could also be the thermostat.
Low coolant, stuck thermostat, failed waterpump, plugged radiator, inoperative radiator fans, etc.
when your coolant in your engine gets a certain temperature,usually 180 degrees,your thermostat opens and your coolant circulates through your radiator and it keeps your engine cool so it wont overheat.
U NEED A THERMOSTAT. THAT IS WHAT HOLDS THE COOLANT IN THE RADIATOR, SO IT CAN COOL DOWN BEFORE IT GOES BACK IN THE MOTOR.
Thermostat, low coolant, inoperative radiator fan, failed water pump, plugged radiator, head gasket.
low coolant ,froze thermostat ,leaks in hoses ,radiator
a. blown headgasket. b. defective thermostat. c. defective radiator. d. no oil, no coolant.
There could be many reasons. Not enough coolant or bad flow, faulty thermostat, low oil. If the coolant freezes then it will overheat. If your car continues to overheat then you should have the coolant flushed and thermostat replaced.