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Discussion Starter · #1 ·
Automotive tire Line Gas Auto part Electric blue
What would cause spark plugs to look like this? There was a very slight amount of oil residue on spark plug threads. These were NGK and I just switched to AC Delco. The engine is the 2.2 with no misfires and idles fine. I check my oil frequently and hasn’t burned any. There was no oil on the spark plug boots. I am using marvel mystery oil in the gas with the recommended amount labeled on the bottle. Would that cause the issue? I also do remote start my car frequently so it does idle a good bit. Any help is appreciated. Thanks!
 

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I have used MMO in the crankcase oil to quiet lifters. It worked. I don't think it is needed in the gas for modern OHC engines. Those plugs are burning oil and it is either the MMO or crankcase oil. Stop using it and see if they clean up. If they still get black then you are at the beginning of an oil burning engine.
 

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Discussion Starter · #4 ·
Looks like it is running rich for whatever reason. Why do you find a need to use the marvel mystery oil ?
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Looks like it is running rich for whatever reason. Why do you find a need to use the marvel mystery oil ?
I've been using it as preventative maintenance or so I thought. Tried to get better performance and fuel economy
 

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Oil/ carbon on the threads is just leakage of air/fuel up the threads. The seal is at the top of the threads.
This is just cooked on carbon since it’s not in the combustion chamber.
An image of the electrode AND insulator would tell more. There is only about .050” of insulator seen on the 4 plugs you show.
 

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Discussion Starter · #6 ·
Oil/ carbon on the threads is just leakage of air/fuel up the threads. The seal is at the top of the threads.
This is just cooked on carbon since it’s not in the combustion chamber.
An image of the electrode AND insulator would tell more. There is only about .050” of insulator seen on the 4 plugs you show.
Thanks for the reply
 
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