Spark Plug Heat Range

[juiceman]

I just changed my plugs last night and the ones I installed were the standard PFR5G-11, the ones I pulled out were PFR6G11. According to the book the ones I installed are the standard ones and the ones I had were colder. I read on the NGK site that it has to do with the ammount of heat the tip can dissipate. If it is too hot you can do damage to the plug and engine and if it is too cold then the car may not ignite the fuel properly

I never got into this before and always installed what came on the car originally.

What are the opinions about heat range? I guess it could depend on the condition of the car.

Mine now runs smoother throught the rpm range than it did before.

[Q45tech]

New plugs always seem better regardless of the heat range!The heat range has to do with how long the insulator is before it contacts the plug shell.

The is a lot of [exhaust] temperature difference at idle vs WOT [something like 3 times less 550 vs 1550F] as at cruise and idle the amount of air and fuel is 1/6th of WOT at 4,000 rpm.

The ideal plug should be warm enough to not foul in the type of driving you normally do...........obviously New York City traffic vs wideopen Arizona could benefit from slightly different heat ranges.

The coil on plug ignition has a much greater latitude as their is always enough to fire almost any plug.

The reason colder plugs work in racing or sustained high rpm is that they suck less combustion chamber heat out thru the water jacket....and all engines work on the heat difference!The hotter plug tip helps burn off deposits whivh might form on higher mileage [blowby engines [oil burners]].

The reason there is a ideal [new normal] and a +- range is so an expert can examine the plug and decide which might be better.