For the second time in a relatively short period, my 83 civic (1500 cc) has blown the head gasket. 1st time, the head was milled to true it and block was checked for true. Appx 400 miles later, another blown gasket. We're not using the the steel gasket .. Honda dealer no longer carries this part so had to go to afte market. As far as I know, neither time did the unit over heat. After the first incident I installed a new heat sensor in the radiator and the fan is working properly. There is no indication of any problems with the head or the block or the cylinders. Can anyone help me with this mystery?