please read my future from these tea leaves (er, sparks plugs)... is it that time?

You're using a rectal thermometer to diagnose a sore throat.....

Let's talk about why you pulled the plugs.
Any other symptoms?

You don't need a cat and a box to determine whether or not your head gasket has failed or not (or both....)
Do a leak-down test......
Check your coolant level regularly.....
You live in TX, right?
That means that there is a high likelihood that HAVE a borescope, or you know somebody with a borescope - and you've already done the hardest part......

 

When were they last changed; do you know? Toyota says every 12 years or 120k miles, whichever comes first.

With your miles, their appearance, since you've already removed them, and doubly so if you don't know the car's full history, I'd just replace.them.

Any cold-start shaking, coolant loss?

 

A little history of the car is included in the OP's thread that he created in September 2025, https://priuschat.com/index.php?posts/3564754

 

Your fear has taken over your imagination and you aren't looking at this objectively... That's not rust, that's combustion residue, which with that type of color means your engine is running a little hotter than before... As for the head gasket you aren't describing those symptoms in this post but you were in your post 10 months ago.

As in, you're making everything way harder / doing a disservice to those trying to help you by starting a new post without referencing your previous post, as well as how many miles are on those plugs. Are we to believe that there's only 20K miles on these plugs or did you not swap these plugs out at 265K miles?

What you need to do is buy a borescope that plugs into your phone (I bought a really nice one on tiktok for $8) and see what's going on in the combustion chamber. If cylinder 1 or 2 look way cleaner than 3 and 4 than yes, the head gasket failed and coolant is washing that cylinder.

But again, you don't explain symptoms of a rough running engine in this post, but you do in previous which may of been an anomaly because you never explain how often it happened.

 

Maybe the problem is you're using 3 Autolite plugs and one Denso?
At least that's the way it looks to me.......................

Bejesus......am I the only one seeing that?

The Autolite plugs are obviously not hitting quite right based on the color. They should be Denso's, which looks to be hitting perfect..........

The more I look, the more I laugh. They're not even the same heat range. Look at the length of the insulators..

 

^what they all said^