Coolant won't get inside the combustion area with the engine running. The combustion pressures are much greater than the cooling system pressure. It will push the coolant into the overflow.
Blown coolant seal cars have a tendancy to overheat pretty quickly. Running with a cored thermostat gives you a decent amount of time before the car even gets up to temp. You can pretty much get where you need to go.
Oh... and that car is a Series 4. On those 1/4 of the way up on the temp gauge is "Normal". Anything above halfway is pretty much overheat area.