Bill,
This will be unfortunately a fairly long post...
The OEM plugs:
NGK - CR8EH-9 (3rd digit is the heat range number
NGK web site showing codes: http://www.kaila.net/tl125/tl125ngkcode.html
DENSO - U24FER9 (check this: http://www.factorypro.com/Prod_Pages/prodh27.html)
I typically don't deviate away from the OEM
plug - as the result of some observations I made while working as a service advisor at an Acura dealership. At that time the platinum spark
plug was all the rage and we had several customers who changed out the OEM pugs for "the next great thing" as the platinum plugs were thought to be. We (at the dealership) had a rash of customers coming in and reporting poor idling, poor acceleration (stumbling & pinging), poor mpg, engine run on, etc. They assumed there was something wrong with the engine as they had just "upgraded" to the platinum
plug. There even were some Technical Bulletins from Honda/Acura to describe the problem - the recommended solution as you'd expect was to reintroduce OEM plugs. This is not to say that aftermarket plugs are bad, just to remind folks that there's more to it than just pulling and replacing the
plug. I'd think that the advantage of an Iridium
plug is longevity, just stick with the proper heat range. the text string I typed into the web search line = "spark
plug heat range codes", vary this some by typing the manufacturer name before the rest of the text eg. = "NGK spark
plug heat range codes"
Bosch description of Heat Range was succinct:
The spark plugs’ heat range is an index of its capacity to dissipate thermal energy. The different characteristics of automotive engines regarding operating load, compression, engine speed, cooling, and fuel make it impossible to run all engines with a standard spark
plug. The same spark
plug may get very hot in one engine type, but may reach only a relatively low temperature in another. In the first case, the air-fuel mixture would ignite on the glowing parts of the spark
plug projecting into the combustion chamber (pre-ignition) and, in the second case, the insulator tip would soon become so badly fouled by combustion deposits that misfiring would occur. To ensure that the
plug runs between the desired temperatures, plugs with different heat capacities were developed. The so called “heat range”, which is assigned to each spark
plug, is used to characterize these heat dissipation capacities. A
plug with a low heat range number (e.g., 2-4) indicates a cold
plug that quickly dissipates heat to the engine block and cooling system, while a high code (e.g., 7-10) indicates a hot
plug that retains heat. By properly selecting the heat range of the
plug, it ensures that the
plug will operate between the
plug’s designed operating range of 500-900 degrees Celsius. In this range, the spark
plug will be self-cleaning, yet will not be hot enough to pre-ignite the air/fuel mixture.
Any help or just more confusion?