You know enough about cars to know what spark plugs do and why they are so crucial to your engine. However, you've heard your professional mechanic talk about hot and cold spark plugs and you had no idea what they were talking about. Here's what you need to know about this intriguing topic.
The Major Differences
Every spark plug has a different "heat range" that is appropriate for specific engines. The heat range is the temperature that needs to be created by the spark plug in order to successfully spark your fuel. Typically, you're going to want between 900-1,450 degrees Fahrenheit for an effective ignition.
The difference between cold and hot spark plugs is in the speed at which they heat. Cold spark plugs are shorter, which creates a quicker temperature transfer, but a lower heat index. On the opposite end, hot plugs are longer with a slower, and more extreme, heating rate.
Cold spark plugs are, therefore, better for vehicles that require a quick burst of energy to start their engine (such as drag racers), while hot plugs are useful for vehicles that need a hotter and more sustained burn (like stock cars).
Factors That Influence Heat Range
Typically, your vehicle's owner manual will include information about the appropriate heat range for your spark plugs, which can help you decide which is right for your vehicle. There are a variety of factors that affect this heat range and they change from vehicle to vehicle. These factors include:
- Mixture of air and fuel – Engines with low air/fuel ratios can use a colder plug, as the cylinder-head will warm up quicker. However, engines with a higher ratio need hot plugs.
- Ignition timing – The timing of your engine greatly influences its heating range. The quicker the timing, the colder the plug (as those extra ignitions raise the temperature of the engine, requiring less heat to ignite the fuel).
- Piston compression – When your pistons operate with a high compression (say, from between 12.5:1 and 14.5:10), colder plugs are necessary as the extra compression will raise the temperature of the cylinder.
Gauging Their Heat Range
Most amateur mechanics and car owners can't tell one spark plug from the other simply by looking at them. As a result, they may not understand how to gauge their heat. Thankfully, manufacturers typically print this information on the box, though often in an obtuse manner.
Spark plugs typically have a number attached to their name that indicates multiple aspects of the plug. Within this number, is one that indicates the heat range of the plug. This will vary depending on the brand, but typically, a lower number indicates a colder plug while a higher one indicates a hotter plug.
The exact range indicated by each number for each brand varies, meaning you have to play a lot of it by ear. Avoid picking the wrong plug by talking to your mechanic first. They can help guide you towards the plug that offers you the best temperature range. Use the information learned here to help give them an idea of what you want. Contact a business, such as Professional Automotive, for more information.