Plug Heat Range (Burnt Pistons)
Spark Plug Heat Range (Burnt Pistons) -- When driving with a heavy throttle, the tips of the spark plugs are heated to incandescence. The heat must travel from the tip through the shell and ultimately into the water jacket of the cooling system before the next compression stroke. If the tip is still glowing when the piston comes up with fuel, the fuel will ignite before the timed spark -- and you've just blown a hole through the piston!
The number on AC plugs reveals the heat range. Example: 42 is a cold plug; 48 is a hot plug. Don't ever go out on the interstate with a hotter plug than recommended.
Having worked on Buicks since 1940 I've seen plenty of blown pistons and the most common cause was the use of non AC plugs. Those "injector" plugs were the worst and the company was put out of business for false claims.
Ralph G. Crisp, #2399, January, 1992.