Report Overheating airlock? in Engine & Ancilliaries/Gearbox Posted June 29, 2016 I flushed the system from the filler cap, took the thermostat off and flushed the block that way, put it all together and filled it with water and flushing agent, after an hours running I flushed again and refilled. It seems to be ok now. Got a new problem with squeal in the cam belt tensioner, see my new post. Such are the joys of Lotus ownership.