hot plug vs cold plug???

[oldmangump]

Could someone pleas enlighten me on the usage of a cold vs a hot plug and the benefits of each for the 258?

Thanks

[Kevin86]

what are cold and hot plugs?

[LEVE]

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what are cold and hot plugs?

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This article says it better than I can....

SPARK PLUG HEAT RANGE

[John_Strenk]

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what are cold and hot plugs?

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This article says it better than I can....

SPARK PLUG HEAT RANGE

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the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber

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Not quite what I learned but maybe that's why I don't buy NGK's.

I learned it's the temperature of the insulator as the mentioned that determined the heat range. Not principly acting like a heat sink removing heat from the combustion chamber.

Hmmm..

[RRich]

"""" the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber""""

True, but better put would be to say "removes heat from the plug's electrode." It's not possible for the plug to actually cool the cylinder by much.

As you cn see it's a "critical balance" between letting the electrode and insulator from getting too hot vs. too cold.

Hotter or colder is actually using something from a different application that's very similar, but slightly different.

If you run one too "hot" you are taking a chance of internal damage - ping, melted pistons etc.
Too cold tends to let oil, carbon, and fuel collect on the insulator and electrodes, those things are conductive. Eventually there's so much build-up there's no more spark, the crud just carries the spark to ground.

Best to stay with the original plugs, including brand, that the manufacturor designed the heads to work with. They spend millions researching what that engine needs under most all conditions.

[oldmangump]

Thanks to all.

Sounds to me that for low RPM'ing jeep duty. We would tend towards the hotter plug to "burn' off the carbon.

How do you specify a hotter plug?

[Jim_Lou]

You're right, kind of. But the only reason to change from the heat range plug you're running now is that it's not working properly. When the engine designers specified the plug to be used they considered the typical use of the engine.

Each plug manufacturer has their own scheme for designating heat ranges. You need to work off of the manufacturer's chart to find a different range.

[RRich]

Actually there really shouldn't be any more carbon build-up at low speeds vs higher speeds. If anything, there's more time for the combustion process to fully burn, so the carbon should (theoretically) be in smaller pieces and no longer a "sticky" ion.
IF the rings and valves are sealing properly, and there's no excess oil or anything else getting in with the mixture - and the right air fuel balance (mixture) is used there should be no carbon left over.

Best to stay with the correct range all the time, unless you have an "oil pumper." Then it's a temporary fix till it gets repairs anyway.

A word of caution - parts store, JCW etc sell "Non Fouler Adapters." DON'T!!!!!!!!!! What they are is an adapter that screws in the plug hole, then the plug screws into that. It's creating a shield around the plug, supposedly keepng the oil off. It works, the plug is able to fire better.
BUT BUT BUT --- The electrode is in it's own little chamber - it gets the mixture burning inside that little chamber, then the gasses blow out through the small hole into the rest of the chamber. Those 3000+ degree gasses blowing out that hole are like a welding torch flame aimed directly at the top of the piston. Aluminum melts at what, 800-1200 degrees? Cast iron at 1800? In short order you get nice big holes through the pistons.

It's an excellent way to stop the oil fouling of a tired engine - it hastens the major repairs.

[GreenTJ]

From experience of old dirt bike (2-cycle) days - had to burn a "hotter" plug if I was climbing to higher altitudes in Colorado because the mixture would richen as the air thinned. We had to carry a couple of plugs with us - one colder for lower and then if (when?) it fouled as we climbed, we'd swap in the hotter plug, but then have to be real careful when we got low to keep from holing the piston. The newer bikes (this was back in the late 70s and early 80s) were largely 4-cycles with fancy carbs that adjusted for thinner air.
Oops - got off track - this is Jeep Short Wheel base! [img]/ubbthreads/images/graemlins/smile.gif[/img]
Like the other guys have said, if the engine is running well and not passing oil, factory spec plugs should not foul.