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sbestca · 09-23-2012, 11:58 AM

It is probably too late for you, but...

Going back 35 years to my automotive training...

The whole point of spark plug heat range is to keep the plug hot enough to burn any deposits off of it without either burning up the plug or pre-igniting the mixture and suffering the resultant detonation. Interesting to note that some engines like Remote Control glowplug engines and top-fuel dragsters both rely on pre-ignition from the hot plug to keep running.

So the right temperature is about 500f if I recall correctly. If the plug is at that temperature it will just be on the verge of pre-ignition, and it won't take much spark to fire it off. If it is cooler, it will take a strong spark to fire the mixture and there may be occasional misfires, which means fuel wasted and an O2 sensor that turns up the richness on the mixture to compensate. So you have to keep the plug up near 500f.

The problem is, when you are just loafing around, like we do when we are trying to save gas, the plug stays too cool. The temp range is chosen for WOT (wide open throttle). Now for a fact if you are racing or pulling a trailer up Pikes Peak, you would want colder plugs in your engine, and it is often done. We however, want a sure ignition while loafing around 98% of the time. Our use of full throttle is very rare and only momentary at that. If you can stand the risk (of WOT use), you could benefit from hotter plugs, at least theoretically.

I have in thepast switched to hotter plugs to get a lean mixture to ignite at light loads and did see a fuel mileage and driveability improvement. YMMV.

So, how do you know what plug to run?
Well, for maximum power we run them at WOT for a while and then pull them out to look at the colour of the insulator. White is baked too hot, light beige is perfect and black is too cold, (or too rich, but this isn't meant to be an all encompassing lesson). So if you pull the plugs out of you car after routine driving and they are black, you are running too cold. Gas and combustion products are being deposited on the cold plug insulator and most likely the engine is misfiring and wasting fuel. You need a plug heat range that puts the beige back into your insulator if you want consistent ignition.

No unicorn here.

09-23-2012, 11:58 AM	#12 (permalink)
sbestca EcoModding Lurker Join Date: Sep 2012 Location: Nova Scotia Posts: 43 Big Blue Caravan - '12 Dodge Grand Caravan 90 day: 21.72 mpg (US) Thanks: 6 Thanked 8 Times in 7 Posts	It is probably too late for you, but... Going back 35 years to my automotive training... The whole point of spark plug heat range is to keep the plug hot enough to burn any deposits off of it without either burning up the plug or pre-igniting the mixture and suffering the resultant detonation. Interesting to note that some engines like Remote Control glowplug engines and top-fuel dragsters both rely on pre-ignition from the hot plug to keep running. So the right temperature is about 500f if I recall correctly. If the plug is at that temperature it will just be on the verge of pre-ignition, and it won't take much spark to fire it off. If it is cooler, it will take a strong spark to fire the mixture and there may be occasional misfires, which means fuel wasted and an O2 sensor that turns up the richness on the mixture to compensate. So you have to keep the plug up near 500f. The problem is, when you are just loafing around, like we do when we are trying to save gas, the plug stays too cool. The temp range is chosen for WOT (wide open throttle). Now for a fact if you are racing or pulling a trailer up Pikes Peak, you would want colder plugs in your engine, and it is often done. We however, want a sure ignition while loafing around 98% of the time. Our use of full throttle is very rare and only momentary at that. If you can stand the risk (of WOT use), you could benefit from hotter plugs, at least theoretically. I have in thepast switched to hotter plugs to get a lean mixture to ignite at light loads and did see a fuel mileage and driveability improvement. YMMV. So, how do you know what plug to run? Well, for maximum power we run them at WOT for a while and then pull them out to look at the colour of the insulator. White is baked too hot, light beige is perfect and black is too cold, (or too rich, but this isn't meant to be an all encompassing lesson). So if you pull the plugs out of you car after routine driving and they are black, you are running too cold. Gas and combustion products are being deposited on the cold plug insulator and most likely the engine is misfiring and wasting fuel. You need a plug heat range that puts the beige back into your insulator if you want consistent ignition. No unicorn here.