Dopey
Registered
With most normal operating engines the coolant will expand and go into the bottle during normal operation. Take a look at cars that only have a "degas" reservoir they are marked for cold and hot level. Also the reason why a faulty radiator cap will cause overheating because it won't let the pressure out. I would not run without overflow bottle, too many what if's when it comes to the thought of coolant ending up on the tires.