Cooling is a major problem with Jetfires. I have two and found the real “culprit” in both was the copper core radiator which does not like working with an aluminum block and the accompanying electrolisis that comes with it! Dissassembling the cores from both vehicles disclosed that a good third of the core was completely blocked with what appears to be aluminum oxide (product of electrolysis). Replace your radiator with an aluminum unit and wave the cooling problems goodbye.
