Spark plug condition plays a critical role in cold weather starting
Spark plugs that work perfectly fine in 70°F may fail in extremely cold weather. Here’s why.
It’s harder to generate a spark in extremely cold weather
When the magnetic field of the ignition coil collapses, it sends approximately 40,000 volts down the center electrode towards the spark plug gap. The voltage seeks ground and the only way to get there is to jump the gap between the center and side electrodes. Standing in the way? A compressed air/fuel mixture that sits between the center and side electrodes. An air/fuel mixture has a higher electrical resistance than air alone. A compressed air/fuel mixture has an even higher electrical resistance.
Before the spark can jump the gap, you need ionization and a conversion to plasma
The 40,000 volts sitting at the tip of the center electrode causes the compressed air/fuel molecules in the spark plug gap to ionize. Ionization causes the gaseous ions located between the center and side electrodes to “line up” so they can conduct electricity. Ionization between the two electrodes provides an electrical path of least resistance, allowing the high voltage to flow and transform the gaseous air/fuel mixture into a plasma state. A spark is plasma*, and plasma heat is what ignites the air/fuel mixture.
Sparks initiate from a sharp edge
Once ionization is complete the electrical flow starts from the sharpest edge of the spark plug’s center electrode to the sharpest edge of the ground electrode. Then the air/fuel changes state from gas to plasma.
Cold air and fuel have a higher electrical resistance than warm air and fuel
Worn electrodes require a higher firing voltage to establish ionization and plasma
Cold air, cold fuel, and worn spark plug electrodes cause a no-start condition in cold weather
What part does the spark plug gap play?
The larger the gap between the center and side electrodes, the higher the resistance. So, the voltage needed to create plasma is directly proportional to the gap size; the larger the gap, the more voltage is needed to jump the gap. The correct gap generates the hottest plasma and exposes that plasma to the largest possible area of the air/fuel mixture, allowing it to propagate across the cylinder.
* There are four phases of matter: Solid, Liquid, Gas, and Plasma.
Posted on by Rick Muscoplat