Whey is my C3 spark plug threads rusty

so I’m checking my coil packs to see if they’re still good and I pulled my plugs and the C3 plug has rusty looking threads. Does anyone know why C3 has rusty threads and not the others? Change the plugs about 1,500 miles ago when I had the last misfire.

 

Water/coolant in combustion chamber
Sorry
Does #3 smell of coolant?

I would definitely recommend compression/leak down test to confirm if HG issue

 

See how clean #3’s plug electrode is?
(Curved part, closest to camera lens)
Getting steam cleaned

 

A borescope....if the top of that piston is shinny clean from steam, and the others are not...
there's your answer....

I've been disparaged for saying cracked head or the head gasket thing.....so I wont...

If your not having misfire codes....then it must not be too bad....yet...
I personally wouldn't worry about it until you do....

You could lose a cylinder and hardly even notice it with it drying out in the first 30 sec....
not the case for us 4 bangers...

I would watch your coolant levels tho...

Unfortunately, C3 and C4 is the center cylinders and that is where the trapped heat stress is the highest...

I would get prepared...on down the road you'll probably have to eventually do a compression test and/or a leak down test......maybe the exhaust gases in the radiator test....

but if your not losing coolant...or dont have gas bubbles coming out the radiator......I wouldn't worry about for awhile.....5vz engines are tough old girls...