A check of the "search" function will show several posts describing thermo valve function.

The device is part of the EGR control system - in conjuction with the EGR solenoid valve and the EGR valve.

You should be able to get one from a dealer.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum