Q: What could cause the ac off engine temp high to come on after replacing the water pump on a 2011 Chevy cruze

It sounds like you may either have a faulty thermostat that may be sticking causing the temperature fluctuation or potentially have a faulty temperature gauge inside the vehicle that may be providing inaccurate readings. The thermostat regulates the flow of the coolant in your car’s engine and controls when the coolant flows in and out of the motor from the radiator by opening and closing at specific temperatures. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. When the thermostat is stuck open it can cause the coolant to circulate constantly resulting in the motor never reaching the correct operating temperature.