Just an update re the OP question, exactly four weeks to renew US passport by mail from Issan. Someone mentioned the US Embassy Thailand website now says 3-4 weeks where previously it said 2-3 weeks.
FYI:
I used the US Embassy Thailand website, filled the form online, printed the form and checklist which needs to be included, paid online using Thai CC, went to the bank to teach them what a 100Bt bank draft is, stapled 2 photos using 4 vertical staples with only 1 staple into the second photo, mailed everything off using Thai Post EMS for ~70 Bt.
My passport issue date is 18 days after I mailed The application. Upon checking the state.gov passport status page, it also showed “passport mailed” that day. Mailed from US passport printing office in Arizona to US Embassy Bangkok.
27 days after I mailed the application, I received an email from ACS Bangkok stating my passport(s) were mailed by Thai Post with a tracking number. Received the following day. Thai Post tracking page was updated about 8 times in 20 hours.
Excellent experience all around, aside from the bank being a bit frustrating.
Btw- Why do they return the 2nd photo? It was clipped inside my old passport, so maybe they think Thai immigration will want it? Why do they say your 2nd passport will be returned 8 weeks later? Maybe if applying in the US?
I did “check the box” for the larger passport, but luckily it is only 5” x 3.5” like all passports. ????
YMMV