Spark plug life

[orcadian]

I seem to find conflicting info about mileage for spark plug change, anyone have a definitive mileage at which they should be changed?  Our early mk3 has just clocked 20,000 and even on the internet these iridium plugs are £25 each.  Our factors quoted £34 each plus vat! 

Ian

[culzean]

Iridium plugs are good for 70,000 miles... search forum for iridium and you will find you can get plugs for less than the rip-off dealer prices...

[orcadian]

Thanks for that info, the iridium plugs in my Daimler SV8 are changed at 80k so I was surprised that one source quoted 20k for this humble Jazz!  I doubt now that at 70 and doing about 6k a year in the Jazz that I’ll ever get round to changing them!  Other bikes and cars to play with too.

Thanks again

[culzean]

Thanks for that info, the iridium plugs in my Daimler SV8 are changed at 80k so I was surprised that one source quoted 20k for this humble Jazz!  I doubt now that at 70 and doing about 6k a year in the Jazz that I’ll ever get round to changing them!  Other bikes and cars to play with too.

Thanks again

You probably already know this but the reason iridium / platinum plugs last so long is that the rare metals resist the erosion by the spark so much better,  so the gap stays within specification for roughly 4 times the equivalent copper alloy plugs....

[orcadian]

Hello again,
Yes, that was my understanding of the rare metal plugs and why I was confused about the 20k change for the Jazz.  My recent experiences with internet suppliers of plugs for some of my bikes leads me to believe that there are some dubious copies out there and that probably goes for the Iridium versions too where there is even more profit.

Ian

[culzean]

Yeah the big brand names are cloned all the time - it is a constant battle to protect your brands these days..and spark plugs are no exception, NGK even have a guide on their website telling you what to look for in the fakes..

[plasma]

Hello again,
Yes, that was my understanding of the rare metal plugs and why I was confused about the 20k change for the Jazz.  My recent experiences with internet suppliers of plugs for some of my bikes leads me to believe that there are some dubious copies out there and that probably goes for the Iridium versions too where there is even more profit.

Ian

Yes thats very true, lots of copies out there, I had a fake battery.

Plasma.

[guest4871]

Is a factory fresh Jazz Mk2 fitted with Iridium plugs?

[jazzaro]

Yes thats very true, lots of copies out there, I had a fake battery.

Both my old vehicles, the bike and the car, started to burn oil and lose compression after an oil change, with the oil bought from Ebay... I'm afraid the oil was not an original Castrol.

[culzean]

Is a factory fresh Jazz Mk2 fitted with Iridium plugs?

Yes absolutely.... the MK1 never got them though.

[madasafish]

Somewhere on Youtube(?) is a video of the iridium  plugs from a Jazz which had done 120k miles and  on the original plugs. They looked fine: gaps not too large and it ran fine...

[sparky Paul]

I ran a Ford Galaxy for 15 years which had platinum plugs, interval was 40k for changing these. After every 40k, the platinum tips were almost gone.

Obviously, you can't regap them, you have to discard them and replace.

[culzean]

Somewhere on Youtube(?) is a video of the iridium  plugs from a Jazz which had done 120k miles and  on the original plugs. They looked fine: gaps not too large and it ran fine...

The other thing about iridium electrodes is that they can be made much finer ( 0,4 mm dia in some cases ) which tends to concentrate the spark ( even more so with the modern 'dual' iridium design,  with fine point for centre and earth ) and  make it easier for the spark to jump the gap.  An electrode made of copper alloy or steel would probably melt if you tried to make it anywhere near that fine, and it would also erode away very quickly.  Those plugs with 2 , 3 and 4 earth electrodes work on the principle that electricity is lazy and will always jump the smallest gap, and when that gap wears it will choose the next smallest gap etc. 

[jazzaro]

Yes.
In the exact point where electrons flow, temperatures reach thousand and thousand degrees, so wear can be quick if the metal is soft. In this picture https://upload.wikimedia.org/wikipedia/commons/c/c3/Spark-plug01.jpeg you can see the ionized air path of the discharge, but also the point where electrons get in contact with the material, point where the temperature will be extremely high, melting the metal.