I'm going to change the coolant on my VX next week and I have a few questions. 1 - Is draining the existing coolant via the lower hose and knock sensors, then flushing the system via the top radiator hose the best way to do it? 2 - Does flushing the radiator that way also flush the heater core? 3 - Does the thermostat need to be removed to check if it is still good or are there other ways to know if it's buggered or not? Thanks.