What does this plug tell you?

[LateFan]

This is a bit different from things I've seen. One cylinder only, #6. Others had normal color and minor wear. My son says it wasn't gooey like it looks, it was hard, he scraped it off.

[cheffy30]

check this... https://ngksparkplugs.com/en/resources/read-spark-plug good luck. sent from hell using tapatalk

[LateFan]

Thanks. Yep, similar to the pics in most manuals. I'd say "deposits" is the closest. I wonder if if's oil, coolant? Looks like there's a bit of oil on the threads (?).

[cheffy30]

It's not uncommon for the head gasket to fail at the #6 end... could be internal if there is no apparent outside leaks. sent from hell using tapatalk

[ForcedFirebird]

Are you able to do a compression test and report back?

[LateFan]

Yes, it's going to be here this weekend and that was on my list. We're adjusting valves etc.

[Italian_Tuneup]

Looks like combusted oil residue. Bad rings will often foul the plug with oil and leave a tarry mess, but bad intake valve guides will continuously admit oil into the combustion process, but in small enough amounts it won't foul. But it will leave behind ashy stuff from the oil. Other identifiers, puff of smoke on startup, puff of smoke after long deceleration when you tip back into the throttle. Really bad guides and seals can show up on a vacuum gauge with a upsy-downsy type wobble of the needle... Best way I can describe it.

[LateFan]

I know at some point in it's past someone overheated it and cracked the head. A "good used" head was tested and put on, but I'm nearly certain it wasn't rebuilt.

[LateFan]

Compression test today :

Tested each one at least twice. Kept climbing through 20-25 pulses.

1 - 180 / 180

2 - 163 / 165 added teaspoon of oil: 190+

3 - 162 / 165 added teaspoon of oil: 187

4 - 180 / 180

5 - 175 / 176

6 - 180 / 180


So those are just at the edge of 10% apart.

Do these seem high for an eta?

[ForcedFirebird]

Not at all. The eta has higher compression and smaller duration cam, so they tend to test higher cranking compression. A fresh b25 stock will do 180-185, but those numbers drop to about 145-150 with a 272 camshaft.

162-180 isn't a deal-breaker as the car will run fine, but as you can see, you have a couple of sticky rings and be burning a bit of oil when the crankcase pressurizes.

EDIT: Odd that #6 compression tested good, and that's the one with deposits.

[LateFan]

Maybe a guide at 6?

I should add, 195,000 miles on this.

[digger]

using any oil or fuel additives?

[LateFan]

None.

Regular Castrol GTX changes, twice a year. He's put 20,000 miles on this car in 7 years. We adjusted the valves this weekend as well, and they were all right on or within .001".

[cheffy30]

you clearly don't drive that little beast enough. she's jonesing for a tease .. drive her. she wants you. she likes you. don't be shy. sent from hell using tapatalk

[LateFan]

I often advocate the Italian tune-up.