Mark, Why not fit a NOS OE (Smiths 85025/.. or the equivalent AC TC.) sleeved thermostat. I have some available that I recently sourced with various opening temperatures ranging from 68:C to 86:C. Kees Oudesluijs NL [demime 1.01d removed an attachment of type text/x-vcard which had a name of coudesluijs.vcf]