well, i'm not an expert, but i don't really see how higher octane would cause an engine to run cooler. a higher octane rating means that the flashpoint (ignition temperature) of the fuel is higher.
by raising the flashpoint, the fuel mixture detonates a little later. without a sufficient octane rating, the fuel could detonate before the piston reached tdc (aka pre-detonation) causing the common problem of knocking.
another common effect of using too low an octane rated fuel is dieseling of the engine when the ignition is shut off.
that all having been said, i can't really see how raising the ignition temp of the fuel would contrbute to cooler water temps. unless it is because the fuel is more completely burned in the combustion chamber and there is less residual fuel making it out into the exhaust before it's completely burned away?
like i said, i'm not an expert
'94 W124.036 249/040 leder; 8.25x17 EvoIIs
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