Been there got the t-shirt... I can understand your frustration. The head gasket had failed on my 1.8 k-series. The mode of failure was exhibited by: 1. Driving the car under normal conditions with the engine heating such that the thermostat opened at 88 deg C. 2. As long as the temperature gauge stayed above 80ish everything was fine. 3. I would then start driving a bit quicker, the temperature gauge would drop and I assumed the thermostat closed. 4. The thermostat would subsequently not open (due to an airlock) and then full on overheating, temperature gauge in the red. On inspection the bottom of the radiator was stone cold whereas the top was baking hot. To fix it I changed the following things: 1. New radiator from Radtec. 2. 82 deg C thermostat. 3. New cap on expansion bottle. 4. Cooling circuit modification according to September 2012 Low Flying including a bleed valve in the top rail. 5. New head gasket in conjunction with the head being skimmed. 6. Importantly match the fan switch to the thermostat. I spent a good half hour speaking to the guy on the Radtec stand at the 60th about this. Mine is 86 to 76 deg C. The proof is the pudding. I did the Cadwell track day the day after everything was fixed. It's been fine since! Good Luck Mark
