Spark Plug Analysis

[Legacy777]

So I pulled the spark plugs out of the motor 2 weeks ago in preparation for the car getting tuned this week. They had 2,649 miles on them over 3 years and have been run with the so-so tune since the motor start up. The interesting thing to note is that three of the four plugs appear to have a yellow coating on them. I’m not sure what’s up with that. I also used my boroscope to check out the cylinders and # 2 & # 3 cylinders had a very small amount of liquid on the bottom of the bores. I’m not sure if it was just condensation, fuel, or oil. It looks rather clear so I am kind of leaning towards condensation. Nothing really jumped out at me as being extremely bad, but like I said the yellow coating/color was a little odd. Here are the pictures. I kept the hi-res so you can click the open in a new window to get the higher res images.

http://main.experiencetherave.com/subar ... /ngkplugs4


Let me know if you guys/gals have any feedback.

Thanks

[dankberries]

High Speed Glazing ? Sometimes has a yellow tint.
Or possibly just additives in the fuel ?

[Legacy777]

Based on the info I read glazing leaves a shiny residue and I don't think the coating appears to be shiny....but anything's possible. Like you said, it could just be additives.

[RoughDiamond]

I've seen that in low-quality fuels or excessive fuel additives.. More like poor gas... There are VERY few "top-tier" suppliers anymore...

[Legacy777]

Thanks for the feedback. I have only put 93 octane in from Chevron or Exxon. I'm not sure if they're considered "top tier" any more. I have added some sta-bil at times since the car didn't get driven much at times.

[RoughDiamond]

Chevron and Exxon are still listed as TOP TIER, and occasionally that will show up in coolant-consuming engines, but usually much heavier.

And octane does not mean "quality". It's only a rating of it's anti-detonation ability (literally the "Anti-Knock Index rating). The additive packages vary widely between retailers.

[volny]

I usually put chevron in mine, but I have noticed that it seem to love shell for some reason...

[volny]

I m not sure about quality control at Chevron honestly, I used to swear by it but they ve had to flush their entire system one time over here after giving bad gas to a bunch of customers...my friend's chevelle ss got all messed up from it

[Mister Anderson]

looks almost like sulfate. Sodium sulfate can be found in ethanol fuels. Most gas stations have around 10-15% ethanol in their fuel (season depending). Leaded fuel will also make plugs kinda yellowish or rusty looking, but since modern cars can't run leaded fuel without destroying O2 sensors, and leaded gas is really only available for aviation you should be able to rule lead out.

http://msdssearch.dow.com/PublishedLite ... age=GetDoc

That's an application for sodium sulfate removal from ethanol. It does have some relevant info on the subject.

Anyway, that's my random thought.

[cj91legss]

I usually put chevron in mine, but I have noticed that it seem to love shell for some reason...

When I had my 92 SS, and when I will have it back again, I always used shell because she seemed to run the best on shell premium.

[Legacy777]

Thanks for the feedback.

That's interesting info about sodium sulfate.

The whole branded carriers (Exxon, Shell, Chevron, etc) is really a market thing. The fuel comes from bulk terminals where it's separated by grade (octane). The fuel additive package is the ONLY difference. Jobbers (fuel delivery trucks) will usually deliver to specific stations, so if a bunch of Chevron stations got bad gas, more than likely the fuel was contaminated at the bulk terminals or during transportation to the stations.

As for octane, I can speak from personal experience that most terminals/pipelines are rather protective of the premium fuel batches so they don't get contaminated or dilluted.