Could you please look at my spark plugs?

[jsap]

I just pulled my plugs on my 97 SL500 for the first time, and I don't like what I see. The car's been running fine, though I've been ignoring some minor uneven idling. But now that I see the plugs, I can see why.
Also, though it doesn't show in these pics, the center electrodes on the 2 plugs I've pulled look like melting ice-cream cones. On both, the electrodes have worn down, much more so toward the ground electrode direction. (It's like a slope going down toward the ground electrode side.)

Plus, the back side of the ground electrode looks powdery, and it's yellow-greenish.

The wet carbon fouling could be because I've been running 91/87 fuel mixture the past two tanks (before that I've been strictly 91), because the ceramic is still fairly clean. But the overall plug is rusty, and I definitely need new plugs.

Could anyone provide some insigtful diagnosis

[AusMBtech]

The rust color on the insulator is normal for a very old plug. They do that usually after they've been take past their normal interval. Have a look in the supressor to check if there's any corrosion in there.

The plug tip is very worn, they've gone too far past their normal interval (i think it's 60,000km/40,000mi from memory). The ceramic looks about the color i'd expect for the 119 v8, you don't want it too white (too lean)

Which ignition system do you have? twin coil? direct ignition/8 coil packs? If you have twin distributors then check the distributor car and rotor for wear and replace if required.

Check your suppessors for correct resistance (with direct igniton) or check the whole igniton lead (inc coil leads) for resistance (with twin distributors).

This is a good step forward to finding your rough idle. (mechanical or efi fuel system btw?)

[jsap]

I have direct ignition. How can I check the suppressors for the right resistance? Which multi-meter from what vendor would you recommend for general testing of cars?

I think the car runs great given the eroded electrode. But new plugs would do be wonders. As far as the fouling characteristics, I don't know whether the 91/87 mix has retarded the timing too much to leave a residue, so I better put in 91 fuel and see how the plugs look after a week. But checking the suppressors would be a good thing, too. I just hope my valve seats aren't going south....

[Hatterasguy]

How long have the plugs been in their? Are they original? They just look like an old plug that needs to be changed.

Btw running a lower octane won't hurt anything but it is false economy. You engines computer will just adjust the timing so it won't ping but your power and mileage will go down.

[jsap]

No, I don't think they're original. The car has nearly 140K on it, and it was starmarked at about 40K or so. But I think the plugs are 50K or older, judging from the oxidation on it.

I think I'll not worry about the electrode eroding, since the plugs are obviously very old. But why the wet carbon fouling is a mystery, since the insulator is obviously free of it. It's probably due to the 91/87 octane cocktail--the timing was retarded, and the combustion isn't complete due to the mix. I'm going to put in 91 gas and change the K&N air filters with Mann paper (I don't want to risk my MAF) and put in new plugs at the same time. If I still get wet fouling, then I'll worry.

Btw, how do I get Bosch from the internet (like Fastlane) and guarentee that I'll get the German ones?

[Southern]

"Btw, how do I get Bosch from the internet (like Fastlane) and guarentee that I'll get the German ones?"

Why not just order from Fastlane.

If you coat the ceramic and the inside of the spark plug boot with dielectric grease, you will greatly help eliminate the rust problem.

The threads on your plugs look almost like new. Did you wire brush the threads? or the threads could have been coated with anti-seize when they were replaced before.