Which statement correctly describes hot and cold spark plugs?

Which statement correctly describes hot and cold spark plugs?

• A. A hot spark plug has a long heat path, causing it to run hotter; a cold spark plug has a shorter path and runs cooler.
• B. A hot spark plug has a shorter path and runs cooler.
• C. A cold spark plug has a long heat path and runs hotter.
• D. Cold spark plugs do not heat up at all.

Answer: (A)

The important idea here is how heat range is determined by the heat path from the tip to the cooling area of the engine. A hot spark plug has a longer heat path (longer insulator nose), so heat is conducted away more slowly and the tip stays hotter. A cold spark plug has a shorter heat path (shorter insulator nose), so heat is drawn away quickly and the tip runs cooler. This is why the described statement is correct: the longer heat path of a hot plug keeps it hotter, while the shorter path of a cold plug makes it run cooler.

The important idea here is how heat range is determined by the heat path from the tip to the cooling area of the engine. A hot spark plug has a longer heat path (longer insulator nose), so heat is conducted away more slowly and the tip stays hotter. A cold spark plug has a shorter heat path (shorter insulator nose), so heat is drawn away quickly and the tip runs cooler. This is why the described statement is correct: the longer heat path of a hot plug keeps it hotter, while the shorter path of a cold plug makes it run cooler.