Ive replaced water pump thermostat and it seems to lose the most water when parked and its cooling down doesn't lose hardly any water when driving
My car has 148000 miles.
You most likely have a leak in the system. I have seen a lot of failures in the heater’s hoses and connections for this model. You typically will need to perform a coolant pressure test with the engine cover in the cab removed to see where the leak is. If you need assistance with this, a certified mechanic from YourMechanic can come to your home or office to inspect your cooling system for leaks and ensure the correct repairs are made.