Q: Water pushing out reservior tank.

This is possibly due to the lack of control of the coolant flow as a result of the thermostat not being in the motor. 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. I would suggest having an expert from Your Mechanic come to your home to diagnose your cooling system.