I like to drive around in old cars. One of my old wrecks is a 1968 VW Karmann Ghia. Because it's air cooled and has stock heads, the engine tends to run hot. This is because the cooling efficiency and compression ratio were designed for high octane leaded gasolene (typical 1960's gas). Modern cars use electronic ignition, fuel injection and closed loop managing power train control modules (PCM). This combination allows the modern automobile to run efficiently with low air pollution on absolute garbage gasolene (a modern technological miracle). Unfortunately this causes problems when driving old wrecks. I've shopped around and found that Shell sells gas which seems to have a better quality. My Karmann Ghia and 1964 Rambler American seem to run cooler on high octane Shell. Keep in mind that if you're driving a modern fuel injected car then it doesn't matter what you use (go for the cheapest with the lowest octane).

Gary