How to Identify Spark Plug Heat Range?
3 Answers
Spark plug heat range can be identified in the middle of the model number. The heat range of a spark plug is represented by numbers, which are typically located in the middle of the model. For example, in the model BP5ES, the number 5 indicates the heat range of this spark plug. Different brands have different heat ranges, and each brand's heat range corresponds to specific vehicle models. Spark plugs are installed on the side or top of the engine. In early designs, spark plugs were connected to the distributor via ignition cables. However, over the past decade, most car engines have adopted direct connections between ignition coils and spark plugs. Working principle of spark plugs: The ground electrode of a spark plug connects to the metal shell, which is threaded into the engine block via the cylinder head. The insulator primarily serves to isolate the metal shell from the center electrode. The terminal nut is the part of the spark plug that contacts the high-voltage coil. When current passes through the terminal nut and center electrode, it ionizes the medium between the center electrode and ground electrode to generate a spark, thereby igniting the air-fuel mixture in the cylinder.
The heat range of a spark plug is an indicator of its heat dissipation capability. You can see this number in the model, such as single digits like 6, 7, or 8 for NGK plugs. A higher number indicates faster heat dissipation, meaning it's a colder spark plug suitable for high-speed driving to prevent overheating. Conversely, a lower number means slower heat dissipation, indicating a hotter spark plug ideal for city driving to prevent carbon buildup. From my experience as a mechanic, using spark plugs with mismatched heat ranges can cause engine pre-ignition, power hesitation, or even valve damage. You can also judge by inspecting the electrode color after removal: a whitish-gray tip suggests excessive heat dissipation (high heat range), while an oily black or dark appearance indicates insufficient heat dissipation (severe carbon buildup). It's recommended that owners refer to their vehicle manual for the factory-specified heat range or use a multimeter to ensure proper electrode gap. Regular spark plug replacement is crucial—typically every 50,000 km—to save fuel and extend engine life. Never purchase spark plugs randomly, as changing the heat range number can cause multiple issues. A simple visual check: normal color should be tan; if abnormal, seek professional service immediately. Safe driving comes first.
As a car enthusiast, I often study spark plug details. The heat range can be directly identified by the number at the end of the model code - higher numbers like 8 or 9 indicate stronger heat dissipation (cold spark plugs), while lower numbers like 5 or 6 mean weaker heat dissipation (hot spark plugs). Cold spark plugs perform better for highway driving to prevent overheating, whereas hot spark plugs are suitable for stop-and-go city driving to avoid starting difficulties. Once I installed plugs with incorrect heat range and suddenly experienced soaring fuel consumption and acceleration stutter - fortunately, I traced it to the mismatched numbering. I recommend beginners check their vehicle manual or use matching apps rather than making random changes. Spark plug color also reveals heat range status: tan indicates normal operation; pure white suggests excessive heat dissipation (high value); black oil deposits signal insufficient heat dissipation with severe carbon buildup. This affects emissions and power - clean or replace them every 3-5 years using proper tools. Driving habits influence heat range selection: frequent highway drivers should choose colder plugs, while short-distance commuters need hotter ones. DIY-savvy owners can inspect plug color after removal, but always prioritize safety over haste. Developing routine checks on small components ensures smooth driving.
