Now you’ve got me thinking …….Did the switch to J4 plugs coincide with the 1959 addition of thermostatic cooling on 5-1/2 HP and larger? Of course the JW being 3 HP did not get a thermostat.
Another thought on the matter – I always thought that spark plug heat range had nothing to do with how hot the engine ran, with heat range only controlling the temp of the spark plug tip to prevent fouling and degradation of the firing tip and it’s insulator. Colder plugs conduct more heat from the tip to the cylinder head, so should make the engine temp run slightly, but maybe not significantly hotter. Is this right?
Dave
