Interior heaters on full blast. Engine running. Cap off the expansion tank and slowly fill the tank with water. What you are waiting for is the engine to gulp, burp or fart. Your problems are caused by an air lock. Hot water cannot run freely through the block and pass in and out of the heater matrix. From time to time, you will have to tighten the expansion tank cap in order to stop the hot water from bubbling out. When the water is just starting to bubble, kill the engine and if possible leave the cap off, allowing the water to cool. After ten minutes you should see the water in the expansion tank going down. This should be happening as water begins to replace the locked air. This procedure should be done over a period of an hour in order to make sure the job is done. A general rule of thumb is when you can feel the hot air in the cab, the air lock at the very least has budged deeper into the system if not gone completly. Best thing to do is wait for the hot air to come through the cab, kill engine and top up system as required.
col, December 2010
