I got this car in March, done a few easy mods, but most of all, doing a lot of maintenance.
Since I acquired the is350 2012, use only 93 and for the last month for those who may not know, am on a RR-Racing tune.
Started swapping the plugs, and noticed them with a lot of residue buildup.

Posting pics for any input.


...

Few more shots




*replacing with the same Denso Iridium 3473 FK20HBR11

engine does not overheat, no missing coolant
I did use half a bottle of VP Madditive Octanium unleaded about a week ago
No loss of power, no white smoke on cold startup, or at idle

 

Initially I was going to say deposits from additives; but then looked at images across Google images. The only comparable I found was on 2-stroke/4-stroke forums where they said it was "normal"; but over time, the plug gap increased causing less accurate combustion needing to slight build-ups. I cannot say that is normal in a V6; but could be due to a combination of the larger plug gap I'm seeing there and maybe that additive you added recently.

For the heck of it, measure the used plugs and tell us the gap on them.

 

You always buy fuel from the same place like 90% of the time? I'd say that additives in their blend likely induced that.

Here is 55,000 miles...

^^ Notice a bit of funk on #5. It wasn't so tight IIRC.

And 50,000 mi later at 105,000 mi.


As you can see those are burning pretty clean.
Mind you I bought the 350 with 51k mi on it having two prior owners. A lease machine for 3 years in CA, then a local had it for 15k and traded it in whereby I became the 3rd owner.

And the street bike with a tune, a lot of ignition advance, and a heat range cooler plug which might be pushing it..



Switch up where you buy gas and take a look at an easy access plug after a couple of tank fulls.

 

Trying 105k again.

 

on the meantime cleaned the PCV and throttle body, and installed a OCC.

Car is so much smoother with the new Denso Iridiums, almost feels as if the car is off when on idle. It has an axle back, and that also has toned down significantly, and used to get a minor burbble when downshifting that is also gone.

I bought the car a few months ago, who knows if the plugs got like that from the previous owner, still going to keep track how the new ones get after a few fuel tanks. There is a Shell a little farther out that has 93 Shell Vpower nitro+. Normally use a Circle K with 93 octane, next few tanks is Shell with a follow up spark plug check.


For the OCC used 3/8 fuel line, made the brackets out of aluminum plates. Had spare rc mufffler baffles and put one inside of the can to help filtering the gas/oil.


2013Fsport thank you for the spark plug pictures, did help a lot.
* * *

baffle out of a rc 1/4 scale muffler

underside, long bolt w spacer to maintain plate around center of can

 

what OCC is this? Looks nice I might have missed it if one of the other replies asked also.

 

is a universal OCC from usual Ebay, cost me around $23 shipped and tax
If you do a search it will show tons of the same item. The only thing is, the provided rubber lines are garbage, buy 3/8 fuel line. The setup I have used 7' (feet).



Installed a similar one in the SUV, does the job.