Does Changing Spark Plugs from 6 to 7 Increase Fuel Consumption?
4 Answers
After changing the spark plug heat range from 6 to 7, combustion will occur more rapidly, but it will not have any impact on the engine. Here is a detailed introduction about automotive spark plugs: 1. Overview: Automotive spark plugs, commonly known as sparking plugs, function by discharging the high-voltage pulses sent through the ignition wires, breaking down the air between the two electrodes to generate an electric spark, which ignites the air-fuel mixture in the cylinder. They can be roughly categorized into standard spark plugs and insulator-protruding spark plugs. 2. Other Information: The fundamental requirements for a high-performance engine include a stable, high-energy spark, a well-mixed air-fuel mixture, and a high compression ratio. The key component of a spark plug is the insulator. The insulator must possess excellent mechanical properties, high voltage resistance, the ability to withstand high-temperature shocks, and resistance to chemical corrosion. Most conventional spark plugs are made of alumina-based ceramics.
Switching the spark plug heat range from 6 to 7 usually results in slightly increased fuel consumption. With a decade of experience in car modification, I once experimented on my own vehicle by replacing the factory-matched heat range 6 plugs with heat range 7. Indeed, I noticed that deeper throttle input was required to get the car moving. The primary reason is that heat range 7 dissipates heat faster, causing the spark plugs to run cooler at low RPMs, which reduces ignition efficiency and leads to incomplete combustion, thereby wasting fuel. After a week with the heat range 7 plugs in my old Accord, the fuel consumption display showed an increase of about 0.8L. The engine also occasionally shuddered, especially during cold starts. Everything returned to normal after switching back to the factory heat range. Therefore, unless your car has a heavily modified engine or is frequently driven on tracks under high-temperature conditions, it's not advisable to casually change the heat range parameter for daily use.
In the repair shop, many car owners ask about spark plug heat range issues. Simply put, switching from 6 to 7 will likely increase fuel consumption. A higher heat range number indicates faster heat dissipation, but the operating temperature of ordinary family car engines is relatively low. After switching to a 7-range plug, the spark plug cannot reach its optimal operating temperature, resulting in incomplete combustion of the air-fuel mixture. Last week, we repaired a Corolla where the owner had replaced the plugs with 7-range ones on their own. As a result, the fuel consumption increased from 6.2 to 7.1 liters, and there were difficulties with cold starts. Upon inspection, severe carbon deposits were found on the electrodes, caused by insufficient temperature. The factory-set heat range is tested and matched; arbitrarily increasing it can easily put extra burden on the ignition coil. If you really need to change it, you should check the manual to confirm the applicable range.
Increasing the spark plug heat range can indeed lead to higher fuel consumption. The principle is straightforward: spark plugs that dissipate heat too quickly fail to reach optimal temperature during normal driving, resulting in weaker ignition energy. With 15 years of experience running an auto repair shop, I've seen numerous cases. For instance, just the other day, a young Civic owner switched from heat range 6 to 7, claiming performance gains, but ended up with 15% higher fuel consumption and rough idle. Cylinder pressure tests showed normal readings, but the spark plug electrodes were blackened, clearly indicating incomplete combustion. I recommend sticking to the factory-specified heat range in your maintenance manual unless you frequently drive on mountain roads causing engine overheating. If you insist on modifications, it's best to install cylinder temperature sensors for monitoring.
