Can someone help me read my old spark plugs? (gasket, MPG, valve)

[mileena202]

Hi, I have a 2007 Toyota Sienna V-6 3.5L 2GR-FE. I changed the spark plugs for the first time ever at the dealer at 262,000 miles. Recommended interval is 120,000 miles. My mileage had dropped by 5-10 MPG in the past few months, so I figured it was the spark plugs. I used Toyota genuine Denso iridium plugs with .044" gap.

Here are my old Denso original plugs, which now have a smaller .033"-.035" gap:









Why are the 3 plugs on the right in the first pic more oily around the threads than the other three?

In the last pic, for the leftmost plug, is that a crack at the base of the grounding strap?

Thanks!

Oh, and the reason I put off changing them for 140,000 miles was because I knew the dealer would charge me and arm and a leg for a 3 hour job, and I was worried an indy mechanic would not have enough skill to do such a complex job (you have to take off the cowl, manifold, wires, etc. just to reach the back 3 plugs!). But since I began losing 5-10 MPG, I figured new plugs will pay for themselves in a few years, and I had a dealer coupon for $350 to do the plugs, ATF change, and coolant change.

[Hemlock140]

They don't look too bad for that many miles, clearly worn out by the look of the electrodes. Those with that tan color look good, but those with the black indicate oil, usually either worn valve seals (Blue puff of smoke on startup) or worn rings (smoke when accelerating hard or when suddenly letting off the gas and coasting down hill. The latter will eventually set a code and make the check engine light come on, so apparently not too bad yet I that's it. The oily threads usually means leaking valve cover gaskets.

[rbohm]

overall those plugs look clean, but as noted rather worn out.

[mileena202]

Thanks to both of you!

Hemlock140: Yep, I was told I have a valve-cover gasket leak. Need to get that fixed!