Change out water pump and thermostat.now it will not stay warm.car at idle will warm up as soon as you take off down the road it will cool down
My GUESS, thermostat installed upside down, or wrong temperature rating, or the new thermostat is faulty.
… and/or not enough coolant and therefore air trapped in the system.
Are you talking about the engine temp or the heater temp?
Does the new thermostat look like this?
including the rubber seal ring?
yes it does. I also found out housing bad a ball check inside no longer will not move .