Sounds like you may need a resistor.
Temperature gauge may drop when heater turned on because additional coolant from heater core is introduced to cooling system - usually this coolant is cooler than what is currently circulating
The radiator cooling fans are turned on when the heater control is set to defrost.This makes for better and more effective defrosting of the windshield
No, a water heater cannot explode if it is turned off.
The water heater is turned off to save energy and prevent overheating or potential damage.
air pockets in the cooling system, start by bleeding the lines, plus there is a bypass for the heater core when you have the a/c turned on, or your heater isn't on, this fluctuate between makes and models. but i would go to youtube and look up how to bleed coolant lines, and that should make it easy for you.
Yes, it is recommended to turn off the water heater when the water is turned off to prevent damage to the heater and save energy.
Yes.
No.
Check your cooling fan
Yes, it is recommended to turn off the gas water heater when the water is turned off to prevent damage to the heater and ensure safety.
The gas valve for the water heater should be turned on when you need hot water and off when you do not need hot water.
No.