Using spark plugs with inappropriate heat range can prevent the machine from achieving promised performance. Before using the spark plug, you should know which heat range means what.
So, what about the context of spark plug heat range 6 vs 7? Rating 6 is hotter with a long insulator nose and suitable for light-duty vehicles. Whereas rating 7 is suitable for speedy vehicles with short insulator noses.
We know that this brief elaboration is not enough to get a definitive resolution in the case of the spark plug’s inappropriate heat range.
In-depth Comparison Between Spark Plug Heat Range 6 vs 7
Please note: This rating strategy (rating 6 is hotter and rating 7 is colder) is applicable for some manufacturers like NGK. At the same time, there are manufacturers who rate 6 for a lower heat range and 7 for a hotter heat range. Here we have discussed considering the base of NGK. For the alternative, please, consider the discussion as vice versa.
To simplify things, heat ranges define the range of heat of plugs they can withstand with. Low heat ranges mean lower heat range means a lower temperature can heat up the spark plugs.
And the higher temperatures mean the plug can withstand higher temperatures.
The table below provides you with a comparison point of view when choosing between spark plugs in heat range 6 and 7.
| Spark Plug Heat Range 6 | Spark Plug Heat Range 7 |
| Insulator nose is long | Insulator nose is short |
| Ignites more quickly | Ignites slowly |
| Hot combustion gases have more accessible areas | Hot combustion gases have less accessible areas |
| Gas pocket size is comparatively smaller | Gas pocket size is comparatively larger |
| Heat transfers to the engine head slowly | Heat transfers to the engine head faster |
| Suitable for light-duty vehicles | Suitable for high-performance vehicles |
Spark Plug Heat Range 6
As mentioned earlier, the spark plug with a heat range of 6 is hotter than the spark plugs with a heat range of 7. And it is a good fit for light-duty vehicles. Here, what we mean by a “light-duty vehicle” also includes your tuned car (if driving within the city-speed limit).
Moreover, this heat rating is not suitable for high-performance vehicles at all.
So, should you go for the spark plug heat range 6? Let’s check its advantages and disadvantages.
Advantages Spark Plug Heat Range 6
Below are the benefits of using the spark plug heat range 6.
- It restricts premature fouling by ensuring an enriched ratio of air and fuel
- Nearly zero or less misfiring and engine stalling
- It can show you how your vehicle’s mechanical power exchange is working; if it is poor, there will be a visible mark (which the auto repair shop will undoubtedly identify)
- Better ignition
- Burns fuel easily
- Burns more carbon deposits
Disadvantages Spark Plug Heat Range 6
Below is the list of issues regarding using the spark plug heat range 6.
- Eventually, this causes an overheating condition, which results in the faster deterioration of electrodes
- Increased fuel-related expenses
- In the long run, it can burn out the valves and erratic of the engine
Spark Plug Heat Range 7
In comparison, rating 7 is colder than heat rating 6 and suitable for high-performing vehicles. Here, we detail its advantages and issues.
Advantages Spark Plug Heat Range 7
Below are the benefits of using the spark plug heat range of 7.
- Can remain cooler at higher temperatures (550°C to 860°C)for a longer period
- More efficient in the case of accelerating
- There is less risk of major engine damage; it may only result in a foul out
- Highly suitable for modified vehicles with a higher cylinder temperature
Disadvantages Spark Plug Heat Range 7
The following is a list of issues with using the spark plug heat range 7.
- It frequently becomes dirty and goes out of work
- Fewer power gains
Why Search For an Appropriate Spark Plug’s Heat Range
Well, as you are curious about the appropriateness of a spark plug’s heat range, it is better to know what issues are associated with the inappropriateness.
- Premature fouling
- Misfires
- Reduced lifespan of electrodes
- Increased waste of fuel
- Major mechanical issue (in the engine)
- Vehicle cannot respond as per expectation while accelerating, and many more
Indications: Existing Spark Plug Heat Range Compatibility
Knowing the advantages and disadvantages of spark plugs with heat range 6 and 7 are not enough to reach a decision. You must be sure that the existing one is not suitable for you before switching.
Here, we’ve listed some common indications showing that the installed spark plug’s heat range is not “okay” with your vehicle.
- Vehicle is not starting smoothly
- Engine is producing a rattling sound while idling
- In moving conditions, you sense a vehicle’s powerless condition for half or a quarter of a second
- The car is shaking unusually while shifting gears (speeding up or slowing down)
- Your vehicle eating more fuel than it supposes to
- Vehicle is not generating the expected power
If you experience any of the above, you should go for a step-up or step-down after considering specialized criteria of heat rating 6 and 7. Let’s check.
Why You Should Switch From 7 to 6 or Vice versa
In this section, we elaborate on why you should consider switching from spark plug heat range 6 to 7 and the reverse.
Switching from Rating 6 (hotter) to Rating 7 (colder)
The below-listed criteria you should consider as those demand switching from a hotter to a colder spark plug.
- You need a higher compression ratio
- The nearby fuel depots supply led types of gasoline
- Your vehicle’s engine is alkyl-fueled (methanol-based)
- You are using a racing car with a nitrous cylinder
- The vehicle primarily travels at a higher speed on highways (long distance; high speed)
Switching from Rating 7 (colder) to Rating 6 (hotter)
The below-listed criteria indicate the need for switching from a colder to a hotter spark plug.
- If your vehicle’s engine supports a rich air/fuel mixture
- Holding back the timing lowers the combustion temperature
- The fuel stations nearby you supply oxygenated or zero-leaded fuel
- If you live in a hilly area with a lot of steep sloping roads
Process of Changing Spark Plug
Please follow the below step-by-step process to switch from spark plug heat range 6 to spark plug heat range 7 and the reverse.
- Step 1: Get the tools and the new spark plug (as per the desired heat range of 7 or 6)
- Step 2: Allow time for the vehicle to cool down
- Step 3: Disable the connectivity with the battery
- Step 4: Depending on your vehicle’s design, remove the coil-on-plug connectors or spark plug wires
- Step 5: Now, take out the spark plug along with the socket
- Step 6: Place the new spark plug
- Step 7: Reconnect all the disabled connections (battery connection and spark plug wires)
We would like to remind you that you should not put too much force into placing the new spark plug. It should get inserted into the threads smoothly.
- Step 8: Take it out if you sense any harshness and the spark plug is not going inside easily
- Step 9: Now, examine the inside threads for obstruction (a mobile torch is a good solution here to inspect the inner condition). In general, rust is the main problem causing such corrosion.
- Step 10: Spray some rust removal and wipe the part with a dry cloth (with the help of a stick; a screwdriver is also ok)
You can check this video for a better understanding:
Final Thoughts
We hope now you have in-depth information regarding the context of spark plug heat range 6 vs. 7. In addition, we would like to mention a few more things.
If you are not an expert in vehicle mechanisms, always listen to the mechanic in the case of spark plug changing requirements. Finally, it is better to stick with the manufacturer’s guidelines regarding the applicable heat range of spark plugs.