Head from a 1988 Toyota 4 Runner, 22 RE Engine...
with 537,500 miles on the head....
oil changes every 20K to 25K.....filter every 5K.
Using Mobil 1,
Here's what she looked like after removed from engine to be replaced with new head... due to finally getting low compression... replaced with head having larger valves and higher compression ratio....
Stuff sorta works, don't it...
note how much sludge and varnish it has all over it...
Sorry for the blurriness... camera has a macro focus issue I need looked at... but pic still gives general idea...