Topic: Spark plugs

[melbill]

I have been reading about using colder plugs. I have found the descriptions and identification of these plugs. Can anyone explain what using colder plugs does. How does it work, when should they be used, etc...
Please explain it on a dummy level, this is new to me.

Thanks a lot

Bill

[sharpxmen]

I have been reading about using colder plugs. I have found the descriptions and identification of these plugs. Can anyone explain what using colder plugs does. How does it work, when should they be used, etc...
Please explain it on a dummy level, this is new to me.

Thanks a lot

Bill

you should only use colder plugs if you are running forced induction or if you experience pinging/knocking - there's no reason for it otherwise nor will it give you any performance gain.

[melbill]

ok, that helps me, but I am still trying to understand what they do. How do they stop the pinging and/or what is their use in forced induction?

Thanks
Bill

[dwtaylorpdx]

The electrode runs cooler, often the electrode gets hot enough to ignite the fuel air mix with out spark causing pr-ignition or pinging.
I use a heat range colder than stock because I have higher compression, run higher than stock RPM I get pinging under sustained wide throttle...
And I tend to run lower octane fuel around town.

Dave

[somar]

not me the book chilton :
the general rule of thumb choosing a spark plug : if most of your driving is long distance ,  high speed travel ; use a cooler plug : if most driving is stop and go ;  use a hotter plug

[sharpxmen]

ok, that helps me, but I am still trying to understand what they do. How do they stop the pinging and/or what is their use in forced induction?

Thanks
Bill

in order to burn the fuel completely the engine runs at a certain temperature in the compression chamber (the volume created between the top of the piston and the cylinder head - the heat range of a spark plug (which is the number that tells you how hot or cold is a plug) is the ability to remove heat from the chamber, the hotter the plug the slower the heat is removed and therefore the chamber is hotter. If it's too hot you get autoignition during compression or uncontrolled burning of the fuel (burns too fast) which is what pinging/knocking is (also called detonation) - it will try to turn the crankshaft opposite to the normal rotation of the engine - in that case you need a colder plug. If the plug is too cold for the engine you have issues with fuel not being burned completely (or too slow) and your motor does not run efficiently (same if your thermostat stays opened in the winter for example, your mpg goes way down).

detonation can have also other causes like compression ratio too high, too much advance, too low octane fuel for the engine or deposits in the chamber that can hold the heat and also increase the compression ratio

the higher the heat range number the colder the plug

[dwtaylorpdx]

Not all plugs do the higher = colder, either NGK or Nipondenso is backwards! Never can remember...

Dave

[sharpxmen]

Not all plugs do the higher = colder, either NGK or Nipondenso is backwards! Never can remember...

Dave

NGK has the higher number to a colder plug (that's what i use, 5 is stock for Jeep, I used 6 and 7). the heat range is that way (the higher the heat range the faster it removes the heat) but the part number might be different (it's a manufacturer choice).

[Jeffy]

funny story my friend had an 86 dodge pickup' and something happened with the carb where when he turned the ignition off the engine stayed running. it kept idling higher and higher as him and his brother is runnning around panicing trying to figure how to shut the beast down... THEN they disconnected  the sparkplugs AND the engine continued to run!! THEN the rpms where at about 4500 and the exhaust manifolds were glowing bright red intul.... the engine slow idled down and stop'd to discover it was now seized....

It's called dieseling.

[sharpxmen]

funny story my friend had an 86 dodge pickup' and something happened with the carb where when he turned the ignition off the engine stayed running. it kept idling higher and higher as him and his brother is runnning around panicing trying to figure how to shut the beast down... THEN they disconnected  the sparkplugs AND the engine continued to run!! THEN the rpms where at about 4500 and the exhaust manifolds were glowing bright red intul.... the engine slow idled down and stop'd to discover it was now seized....

if it's a manual you put it in gear and release the clutch with the brake pressed. If it's auto tranny then you'd have to either cut the fuel or cut the air (cover the carb opening with your hand). usually its caused by deposits in the chamber (mostly on high mileage vehicles) or by low grade fuel.