Abstract: A car wash system for large vehicles, such as trucks and busses, in which the arrival of a vehicle initiates a process of directing hot water from a supply tank through a relatively long supply line to a spray system. Water standing in the supply line is prevented for a time from going to the spray nozzles and, instead, is directed back to the source. This allows the temperature in the line to reach a predetermined desired value before washing is started. Water is recirculated at a faster rater than it is dispensed once the desired temperature has been reached.