A couple of weeks ago I some oil that looked to be leaking from my number 7 plug so I swapped it out with a bosch +2 and that fixed the oil seepage. However, yesterday I replaced all of the plugs and the bosh +2 that has only been in the engine for two weeks and it looks like this:



Here's one of the original NKG plugs that has about 10,000 miles on it:



What are the main causes of carbon build up like this? What steps should I take if any? Although I will note it runs great and I'm not having any issues at all.

 

Anyone?

 

cheap gas, too much gas (running rich), oil blow-by (piston rings), PCV system clogged up, weak spark, valve seals or valve guides admitting too much oil.

See plug chart and http://www.ngksparkplugs.com/tech_su...qs/faqread.asp

 

Thanks Buzz. The previous owner did say the half gallon bottle of Lucas fuel additive in the back was to make cheap gas the same as "high octane"... I'm not burning any oil at all. I'll have to read up on the pcv system but it sounds likely it'll be fixed with the new plugs, and correct octane fuel. I suppose the planned seafoam induction cleaning I'm doing this weekend could only help? Thanks again.