Importance of Heat Range
The heat rating is a measure of the amount of heat dissipation.The heat range of a spark plug is the range in which the plug works well thermally. The heat rating of each NGK spark plug is indicated by a number; lower numbers indicate a hotter type, higher numbers indicate a colder type.
![](https://www.ngkntk.in/wp-content/uploads/2020/01/HEAT-RATING-AND-HEAT-FLOW.jpg)
![](https://www.ngkntk.in/wp-content/uploads/2020/03/screenshot-docs.google.com-2020.03-1-1-891x1024.png)
Effect of Selecting Wrong Heat Range
![](https://www.ngkntk.in/wp-content/uploads/2020/01/HEAT-RATING-TOO-HIGH.jpg)
When the heat rating is too high
The spark plug temperature remains too low and causes deposits to build up on the firing end; the deposits provide an electrical leakage path that gives rise to a reduction of spark.
When the heat rating is too low
The spark plug temperature rises too high and induces abnormal combustion (pre-ignition) ; this leads to melting of the spark plug electrode that could cause problems such as piston seizure.
![](https://www.ngkntk.in/wp-content/uploads/2020/01/HEAT-RATING-TOO-LOW.jpg)