<div class="FTQUOTE"><begin quote>Originally posted by: reconranger


Doesn't surprise me....most folks have never even read their owner's manual! Most folks don't change to lighter oils for winter either.....</end quote></div>

If you read your manual so closely than just do what it says!

 

Predetonation is normally under compression which will cause a knock as the cylinder mass decreases from the piston moving up, both valves closed.
Normal detonation may not knock as a valve is opening when the piston is going down in the cylinder, decreasing the cylinder mass.

A colder spark plug disipates heat more quickly (hotter head) and a hotter spark plug disipates heat slowly (cooler head). Just the opposite one would interpertt as the heat range indicates. If you install a colder plug in a liquid cooled engine, the quicker heat transfer would raise the coolant temp.

----- Gimpster -----

 

OK
to make the spark plug under combustion more clear here is an example for future reference
To indicate the hot plug tip and the cold plug tip
Take 2 identical 1/2 inch by 4 foot long rods and stick them in the ground. On the top of one weld a 3 inch round by 12" long solid steel cylinder (hot plug tip). On the other weld a 3" round by 4" long solid steel cylinder (cold plug tip). The longer cylinder is the hotter plug. Now take your torch and heat up both of them red hot. Which one takes longer to heat up ? The rod with the longer cylinder takes longer to heat up (hotter plug) under combustion and cools slower. The shorter one (cold plug) will cool quicker, heat up faster.
The longer one, hotter plug will raise the cylinder temp the next time it fires as it stays hotter longer than the short 'cold' tip.
Like I said at the beginning of all this, It is backwards from what the heat range indicates.

Do I make the team yet ?

----- Gimpster -----

 

I think one thing we have to keep in mind is that the cold plug has more of its insulator touching the metal that threads into the head; therefore, it dissipates its heat much faster.... even though it has less mass to heat up. I dont think the 12" vs 4" rods is a good analogy unless you add a 12" hunk of aluminum to the 4" piece of steel and a 4" aluminum to the 12" steel rod.... and then also add a cooling fan to the aluminum and heat them using an oven instead of a torch.

If we study the pic I posted from NGK's site carefully, we see the ceramic touches more metal in the cold plug and less of it is exposed to the combustion gases. In other words, a bigger door for heat to escape and a smaller door for heat to enter. Hence, the plug stays cold.

Cold plug = small door for heat to enter, big door for heat to escape.
Hot plug = big door for heat to enter, small door for heat to escape.

Since the cold plug has a smaller door, and gathers less heat, it can only dissipate less heat,,, even though it is really good at dissipating lots of heat.

Since the hot plug has a large door, and gathers lots of heat, it can only dissipate small amounts of that heat per unit time, because the escape route is smaller than the entry. Therefore the hot plug retains lots of heat and has no other exit other than the exhaust.

Seems to follow then that the head temps wouldnt vary that much between the 2 plugs. Whether the plug gathers lots of heat, but can't transfer it to the head very well, or the plug can't gather very much heat but yet can transfer it very well seems like a different way of saying the same thing.

Would you rather makes lots of money and be taxed to death or make little money and pay very little taxes? The net result is the same. ....or at least the difference would barely be significant.

At least that's my thinking.... [img]i/expressions/face-icon-small-confused.gif[/img]

 

hehehe, you're confusing yourself

The way you have described it, Honda would be saying Reconranger should be installing a colder plug in his unit. Since it disperses heat quicker when the unit is lean from the cold temps.

Look beyond the aftermath of the combustion. If you install a colder plug, it will disperse more heat to the head quicker. This will keep the head hot from transfering more heat. A hotter plug will retain more heat in the tip and disperse less heat to the head. A colder plug's tip heats up quicker and can cause piston failure by the heat transfered from the past combustion to the head which is hotter than the past combustion heat transfer in the hotter plug, dispersing the heat slower to a colder head.

Hence, Honda recommends a hotter plug in colder temps.

If I put in a hotter plug in my Foreman, the fan will run less because the head is running cooler from the slower heat transfer to the head (gives the head more time to cool). The stock plug in the unit in a cold dlimate makes the fan run more because it is colder than the recommended hotter plug which disperses heat transfer to the head slower, keeping the head cooler from less heat transfer, and the fan running less.

----- Gimpster -----

 

I'm not sure the amount of heat the plug transfers to the head would make much of a difference to the temperature of the head... considering how much surface area of the head is directly exposed to combustion and heat, I would think the heat that comes to the head via conduction from the plug would be such a small drop in the bucket as to be insignificant?

 

<div class="FTQUOTE"><begin quote>Originally posted by: JeffinTD

I'm not sure the amount of heat the plug transfers to the head would make much of a difference to the temperature of the head... considering how much surface area of the head is directly exposed to combustion and heat, I would think the heat that comes to the head via conduction from the plug would be such a small drop in the bucket as to be insignificant?</end quote></div>

That's my point as well.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Gimpster

The way you have described it, Honda would be saying Reconranger should be installing a colder plug in his unit. Since it disperses heat quicker when the unit is lean from the cold temps.</end quote></div>

Exactly! lol.... If your engine is lean, use a cold plug. And that's what NGK says too. [img]i/expressions/face-icon-small-smile.gif[/img]

<div class="FTQUOTE"><begin quote>Originally posted by: Gimpster

Hence, Honda recommends a hotter plug in colder temps. </end quote></div>

I'm speculating that they do that because of hard starting issues more than anything else. I flooded a little 110 with the choke trying to get it started the other day. I had to take the plug out and clean it really good. I was thinking a hot plug may help that.

I can't comment about your fan running more or less with which plug. There may have been other variables at play (ie. temp, humidity, work load, etc).

All I know is that its a stretch to believe a hot plug makes the engine cooler.

 

I'm also not convinced a cold plug actually "cools" the combustion chamber by transfering heat to the head and better than a hot plug would.

As I said before:
Cold plug = small door for heat to enter, big door for heat to escape.
Hot plug = big door for heat to enter, small door for heat to escape.

Since the cold plug has a smaller door, and gathers less heat, it can only dissipate less heat,,, even though it is really good at dissipating lots of heat.

But, I'm no thermodynamics expert... I'm just Randy and sometimes I know just enough to be dangerous. [img]i/expressions/face-icon-small-tongue.gif[/img]

 

hahaha, dangerous, that's a good one
I'm no engineer eather

I think we have beat this topic to death

I'll give it a rest.

Thanks for making me think you all !!

[img]i/expressions/beer.gif[/img]

----- Gimpster -----