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Why worn spark plugs cause no-start problems in cold weather

How worn spark plugs affect cold weather starting

Here’s the simple version: Worn spark plugs that start your engine in 70°F weather can cause a no-start in cold weather. Here’s the technical scoop on why that happens.

Spark ignition is a three-part process; ionization, plasma creation, and flame creation

On a modern engine, the ignition coil develops 40,000 volts and sends it to the spark plug where it’s supposed to jump the gap between the center and side electrodes. Forcing voltage to jump a gap is hard enough in air, but it’s even harder when the gap is filled with a compressed non-conductive air/fuel mixture. In order to get voltage to flow across the gap, the air/fuel mixture must become conductive in a process called ionization.

The 40,000 volts waiting the center electrode causes the ions in the air/fuel mixture to “line up” and become conductive. Once the line-up is complete, the voltage travels across the ion gap “bridge” creating plasma that’s up to 60,000 °K. That’s the heat that ignites the fuel.

Worn spark plugs don’t create enough heat

Sparks always jump from the sharpest edge of the center

worn spark plug

The spark jumps from a sharp edge on the center electrode to the side electrode. As the center electrode wears, it rounds off, resulting in shorter spark duration and misfires.

electrode to the sharpest edge of the side electrode. Unfortunately, the electrodes on worn spark are rounded over and the gap erodes and becomes larger. So more of the high voltage energy is wasted overcoming the wider gap and rounded electrodes. The result? A shorter spark that’s not as hot.

Now, here’s where the cold weather comes into play

• A cold air/fuel mixture has a much higher electrical resistance than warm air and fuel. So it takes even more energy to ignite the fuel in cold weather than warm weather. That’s energy you don’t have with worn spark plugs. A good portion of the available energy has already been wasted trying to jump the larger gap.

• The cold metal engine tends to quench any flame that’s created.

That’s why so many car owners are shocked that their engine that started fine on November 15th, doesn’t start on December 15 when only thing that’s changed is the outside temperature.

©, 2022 Rick Muscoplat

 

 

Posted on by Rick Muscoplat



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