“Corona staining” spark plug Qs

[Faawrenchbndr]

So this is a new one for me. Odd staining on the plug porcelain. No presence of carbon tracking, just this odd ring, looks like a rust stain.

Runs fine, no missing, smooth idle. Little to no wear on plugs, look good at 33.5k

 

[melk]

3x recent spark plug changes on 3 different engines all looked similar. I don’t remember past plugs looking like that but I guess it’s been a while since I changed a set.

 

[Cujet]

That is very normal. Today's spark plugs are changed much less frequently compared to years ago.

 

[Faawrenchbndr]

Thanks guys…….seems as if this was considered normal. But, needed another opinion

 

[dogememe]

Normal.

 

[Number_35]

That is very normal. Today's spark plugs are changed much less frequently compared to years ago.

The debate back in the day was whether to change plugs twice a year (regardless of mileage) or to change at 10,000 miles (regardless of time).

 

[oldcodger]

But what causes this stain?

 

[martinq]

But what causes this stain?

I thought it might be a slight gas leak from the combustion chamber but I'm really not sure. Di-section might be helpful.

 

[Marcozi]

It looks like the plugs have leaked miniscule amounts of combustion gases over the years.

 

[Faawrenchbndr]

But what causes this stain?

Well…… a search stated the staining is created by static electricity and heat acting upon dust and dirt.
Specifically states it’s not leaking combustion gasses or a faulty spark plug.