Cooler running motor w/NGK iridium plug?

[dragonchef]

Took a 200 mile run today after installing my (non-group-buy-dang-it) plugs. Seemed to be running 1 to 2 bars cooler than normal...is this possble...also changed the oil at the same time.

 

[lnewlf]

If you install plugs with a colder heat range combustion chamber temps will be less..also less chance of detonation but greater chance of fouling and carbon buildup..Good idea to stick with a plug within the factory specified heat range.

 

[Cdogman]

I dunno.. My bike has run both. My bike regulates itself ad dead center in the bars and stays there under all but extended long slow or idle conditions.

The FJR (my genII anyway) does a good job of heat regulation as designed

 

[mike25]

If you install plugs with a colder heat range combustion chamber temps will be less..

HUH?????????

 

[Ignacio]

Not bloody likely. A wive's tail that just won't die.

Moved thread to it's new home.....with prejudice. <_<

 

[Randy]

Took a 200 mile run today after installing my (non-group-buy-dang-it) plugs. Seemed to be running 1 to 2 bars cooler than normal...is this possble...also changed the oil at the same time.

Possible? yes. Probable and logical? me thinks not.

 

[UHOH]

Took a 200 mile run today after installing my (non-group-buy-dang-it) plugs. Seemed to be running 1 to 2 bars cooler than normal...is this possble...also changed the oil at the same time.

my experience was these same plugs made no difference.

bike ran well before, ran well after.

temp is @2 bars when moving.

 

[lnewlf]

Uh-I've known since I was 15 that colder plugs lower cylinder head temps--Try running cars at the drags for 25 years as I have and you might notice this..Why do you suppose that plugs come in different heat ranges? If you want to run 23 degrees of advance for a good hole shot , you damn well better run cold plugs.

 

[Randy]

Uh-I've known since I was 15 that colder plugs lower cylinder head temps--Try running cars at the drags for 25 years as I have and you might notice this..Why do you suppose that plugs come in different heat ranges? If you want to run 23 degrees of advance for a good hole shot , you damn well better run cold plugs.

Damn you for making me read!!!!

Someone told me long ago (ok, I lied...I just read it here) that spark plugs work as a heat exchanger - by pulling heat from the combustion chamber, you transfer that heat to the cooling system.

You said in a previous post that colder plugs lower combustion chamber temps and you also said that colder plugs lowers cylinder head temps.

Seems to me that you can't have both - cooler combustion chamber temps AND cooler cylinder head temps. If you're simply exchanging heat, the heat has to go somewhere.

I'm guessing that is why superbikes have extremely large radiators. They're generating more horsepower resulting in the need for a cooler plug which, in turn, results in more heat being transferred to the cooling system neccesitating the need for the bigger radiator. Since most FJR riders won't be installing oversized radiators, wouldn't a cooler plug make the cooling system hotter? In this theory, a hotter spark plug would result in less heat being transferred to the cooling system, but, too high heat in the combustion chamber could result in catastrophic spark plug failure.

Any flaws to any of this logic?

 

[ionbeam]

Where is Jestal? He should be all over this thread :lol:

Randy, basically you have it right.

The amount of heat that a spark plug receives determines its 'heat range'. As Randy has said, plugs that disperse a lot of heat are Cold Plugs and the ones that don't disperse heat are Hot Plugs.

Plugs with long insulators in the combustion chamber have a lot of surface area in contact with the flame and gas pocket. The heat release path from the tip of the insulator to the metal housing is long permitting the electrode temperature to easily rise.

Plugs with short insulators in the combustion chamber have much less area in contact with the flame and gas pocket. The heat release path from a short insulator to the housing makes heat dispersal very good. This keeps the tip of the electrode cool.

Spark plugs have a temperature zone where they work best for a particular application. The lower limit is roughly 500°C; below that temperature the plug stops being 'self cleaning' and starts to collect carbon. Above 950°C the electrode becomes so hot that it will reach pre-ignition temperature.

When a plug's electrode drops below 500°C carbon generated from incomplete combustion gets deposited on the insulator. This coating of carbon makes the insulator’s resistance drop. Low resistance causes the ignition spark intensity to be reduced and this results in difficulty initiating combustion. Above 500°C carbon is burnt off by the combustion temperature.

As the plug's electrode reaches 950°C or higher, the electrode is so hot it starts to work as a 'glow plug' which then initiates combustion without a spark. The electrode will rapidly erode and the insulator may be damaged under this condition.

Most high performance engines tend toward short plug tips whose temperature does not rise easily at high speeds, thus preventing pre-ignition.

When you have a selection of plugs lying around you can tell a cool running plug by the length of the insulator that extends into the combustion chamber. Short plug insulators are cool plugs and long insulators are hot plugs.

 

[Fred W]

So to continue on what Ionbeam said above: The heat range of a particular plug determines how hot the plug will get thereby effecting if it will foul (too cold) or cause detonation (too hot). But it has little to do with cooling the combustion chamber or the head.

 

[charismaticmegafauna]

'dragonchef': Cooler running motor w/NGK iridium plug?

'Randy': Possible? yes. Probable and logical? me thinks not.

'iombeam': Randy, basically you have it right.

While I certainly find all the "heat-range" dissertations elucidating, they're not particularly germane to the OP's query.

The irrefutable answer would be: the temperature of the FJR's cooling system is controlled (on the low end) by the coolant thermostat's opening-temperature setting and (on the high end) by the thermostatic switch that turns on the fan/s.

But -- what about in-between temps? Could changing spark-plug brand and construction-type cause a different temp gauge reading?....maybe? But, probably not likely....

But -- what if he installed a hotter spark-plug?... an 'alot hotter' one? Would he notice a small difference (hotter) in the temp-gauge reading? :huh: :blink:

p.s. a 'cold' plug (even, a really cold one) will not foul if the ignition system is powerful enough.

 

[C&C]

Cold and hot plugs refer to the temperature that the insulator will get when combustion occurs; the combustion temperature doesn't change (to any effect) just the plug (so as to keep itself clean).

 

[lnewlf]

Most of this is irrelevant to the FJR due to the excellent cooling system and low stressed motor..My air cooled FJ1200 was prone to heat related problems-even melting piston crowns..Long accepted fixes were to fit a larger oil cooler and less restrictive exhaust,also run a richer mixture and one range colder plugs which as mentioned act as a heat sink- doing these mods reduce the chance of excessive combustion chamber temps which might burn exhaust valves, warp heads and melt piston crowns. I did this to my FJ and at 80K miles the cross hatch could still be seen when I tore it down for a big bore kit. I never rode it in extremely hot conditions like 90 degree traffic jams or the FJR either-I've never even had the fans come on..