That is not being caused by your thermostat. Your thermostat should be fully open at 195, if it is a stock thermostat. The coolant will still warm to 210, but if it is getting around 190 then you should be getting good consistent heat. Getting the engine twenty degrees warmer will just warm the heat that much more. The fact that it goes down and comes back up illustrates that there is air in the system. Every time it goes down, immediately top it off before it comes back up. Once you do that it should help you out.
It also might help to flush the heater core. You would just take the hoses off, connect your water hose to one of the hoses, and turn it on, just with low pressure to start with. Once the water starts coming out clean, turn up the pressure. Do this for a few minutes. Then put everything back together and bleed the cooling system again.
Sunday, November 26th, 2017 AT 6:34 PM