I have just changed the thermostat on my Skoda Felicia 1.3 petrol engined car of 2000 vintage. The whole unit, including temperature sensor, thermostat and housing was fitted. As per the manual, the coolant was topped up with the temperature sensor and expanion tank cap removed, the engine running and the heater set at full. Whilst adding the coolant a lot of air bubbles were surfacing. After well over half an hour, these appear to have subsided, hence I presumed that any air in the system had been expelled. The temperature sensor was re-fitted and the coolant topped up via the expansion tank, to the correct level. Throughout this procedure the temperature gauge did not fluctuate, but rose gently until the fan kicked in and it dropped back to normal. I then took the car for a 20 mile run, along a variety of roads, including motorways, A and B roads and three town centres. During this trip which lasted over an hour, the temperature gauge fluctuated to just below the top red marker and then dropped back to normal. This occurred on 6 separate occasions on all the roads traversed. Furthermore, the heating which was fierce, cooled just before the gauge rose to the danger level, dropping back to normal a minute or two later, when the heating would return. When I got back home the expansion tank required 800 cc's of coolant to bring it back to the required level. Your thoughts on the possible cause and solution to this problem would be most welcome.

Raymond Wight, 31 Byron Road, Greenmount, Bury, Lancashire BL8 4EN

Telephone No: 01204 886562