6 years after I bought the car, I started blowing heater cores. The lower block is rebuilt but I did that 2 years ago and didn't have a problem. I have a Steeda aluminum radiator but although I have put in 4 of those, I haven't changed one in 3 years and have had them from day 1. We even put in t's to provide a simultaneous bypass so that if the pressure got too great, the water had 2 paths. Nothing else has blown and pressure tests are showing any issues. We even replaced the thermostat to no avail. If anyone has any ideas, I welcome them.