I replaced my valve cover gasket (Oil in the plug tubes. Again...) and spark plugs last night, and like always, I marked the old ones as they came out.

The plugs were installed in December 2015 at 75,488 miles. They have about 10,600 miles on them. Here they are:





I replaced the plugs when I first purchased the car in July 2013 at 57,620 miles. The plugs that came out had about 18,600 miles on them over a period of 14 years. Here they are for reference:



So I'm seeing that the number 3 plugs look pretty fantastic compared to the others, with very little deposits on them. 2, 4 and 6 look to have heavy deposits on them.

Can anyone read into them? Any experience with your own plugs?

-Nick

 

While there are certainly deposits on them, they don't look overly worn or oily-wet. "If it was me" I would probably put a points file to them, regap and reinstall. But plugs are relatively cheap so no big deal there. That said, I have never felt or seen any difference in changing spark plugs in any of my vehicles. I have done it religiously with caps and rotors, but not ever felt a difference. Maybe its me, maybe its the quality of my cars.... or quality of my parts?

 

Thanks Jerry,

It's funny you mentioned feeling no difference, because I forgot to add that after changing the plugs and valve cover gasket, and resetting the ECU, the car seemed to liven up markedly! I got on the highway and it had pull like I haven't felt from the car in a long time. For what it's worth, it does seem to idle better as it seems there was a slight misfire before. Time will tell if it remains that way.

Any misfire could certainly be from the substantial amount of oil in the majority of the spark plug wells

 

They almost look like an additive has been put in the fuel.

Say it ain't so.

 

No additives, Mikey. Always used at least 91 octane, and often 93.

My car does emit a puff of oil at each startup after sitting for more than a couple hours. Valve stem seals I think.

 

Hi Nick,

NGK has some helpful photos at this link:

https://www.ngksparkplugs.com/about-...d-a-spark-plug

From the photos it appears the deposits are baked on oil - is that your impression? Oil in the plug wells won't help, but it could also be due to the typical XJ40 hardened valve stem seals or your piston rings may be worn.

Cheers,

Don