Spark plug question

120k. that being said, i'm not sure i've seen that brown ring before. was it performing poorly?

 

The coils are not recommended to be changed....until they fail. I'll gladly take your old ones if you are throwing them out

The spark plugs can probably go much longer than 120k miles, so you are in the clear.

 

I was recently watching an "Eric the Car Guy" on spark plug change, and he mentioned that brown, burnt looking zone, deemed it normal. I think he called it "corona" or similar?

 

corona should be yellow. if it's brown, don't drink it.

 

I think the discolouration is from the rubber or whatever on the coil part. It's pretty normal. I've seen it on many different vehicles.

Those plugs look like it was time. Notice the electrodes are rounded. That increases the voltage necessary to jump the gap.

They use Iridium because it melts at a -very- high temperature and is -very- hard, so it lasts a long time. It allows them to use a very thin electrode, which lowers the voltage required to jump the gap and concentrates the spark at a more precise location, so the engine performance can be better predicted. Of course, because Iridium is rare and hard to "machine", the plugs are expensive, but they last so long it's not a big issue.

 

I think that the brown ring of soot on the insulator above the metal nut is due to very slow leakage of the exhaust gasses past the interior rubberized, donut-shaped ring gasket that is compressed between the metal nut/thread part and the ceramic insulator part. My experience is that the gasket slowly degrades over time and use , and that lets a small amount of combustion gasses pass by, creating the soot ring over time. My judgment would be that the presence of that much soot is a sign the plugs should be replaced. When the gasket degrades further, the leakage increases and the accumulated soot can provide a path for the high-voltage spark to slide down the top side of the plug, causing a misfire.

 

nope

yup. completely normal. I see that all the time in toyota cars with long life plugs.

 

All normal. The coils normally do last a long time. I see you are in Texas (hot) -- did someone recommend replacing them?

They normally last 200k + .... I have not looked into the failure rate. It does give pause -- due to the design - a coil failure would require the wipers etc to be removed again .. a much bigger job vs a typical car.

On most toyota's it's a 5min job -- one bolt.

 

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I don't plan to mess with my gen3 until I see 150k

 

Everyone's pushing the limits on the spark plugs lol

 

Yes, this is a reasonable theory.

My 2004 has 221K miles on the odometer. I recently replaced the iridium spark plugs which had logged ~120K miles. One of the four removed plugs had the brownish ring, although not as dark as shown on the OP's photo. The other three did not have the ring.

 

Just changed mine after 120k ...last change was done at 60k,order is 4 3 2 1

 

Interesting that 3 shows fewer deposits on the insulator compared to the other three. What do the porcelain tails look like - any staining as depicted in the OP's photo?

 

I'll have to take pictures of mine and post it then, I've changed it at 114k miles and forget how they look like lol.

 

Oh heck, took this out of my daughter's Pilot yesterday, guess it was time.

 

Did that engine suffer from pinging?

 

Nothing untoward, according to my daughter. I asked her if she noticed any difference with the new plugs, she didn't really.

All the other plugs looked not bad, fairly crusty, this one was the worst. Gaps weren't opened up to speak of, I guess that's the norm with these high end plugs.

 

Uh, to me the shedding of prices of the porcelain insulator would be a sign of rather severe overheating of the tip of the plug. 2-cycle engines with that would be prone to detonation or seizing of the piston in the sleeve . 4-cycle engines could also have problems depending on where exactly that piece of porcelain went. Best case was out past the exhaust valve. Second best was jamming a valve. Worst was cracking top of piston or ring. But I would react strongly to that plug and if it was on a 2-cycle engine, I would switch to a lower heat range plug. Maybe check injectors on that cylinder for being partially clogged?