I pulled thermostats (why? see below*) from several (8) old motors/ cars (84-92) I had around. List temp in C except as noted) w/brand in "":

- 71 (159.8F)
- 82 (179.6F)
- 82 "Wahler"' (broken)
- 82
- 180F (not marked in C) - no vent.
- 87 (188.6F) "Volvo Calistat"
- 92 "Wahler" (broken)
- 92 (197.6F) "Calistat"

For me, a 87C (~190F) seems about right for summer & winter driving (OH). 92C seems hotter than necessary here. But <87C seems too low - low oil operating temps are hard on an engine. Maybe they're best in a more-southern climate.

Notes:

1) 2/3s had the vent up (at 12 o'clock). I read on this forum that that was requisite.
2) The one marked 180F didn't have a vent at all. I 'd guess this was from a parts store "Yeah, this'll work".
3) Gaskets (rubber ring) seemed matched with thermostats eg. some thermostats were slightly smaller (diameter) and took a thicker gasket.
4) There seemed to be a top & bottom to the gaskets but this is probably from wear.
5) The two (brass-colored) Wahlers were broken in the same way: the bridge on the top snapped and the spring pushed the valve to one side. The break was not at a seam or press-weld. The silver-colored Calistats seem stouter. "Seems": this is a small sample size on which to say "Wahler" sucks. I note that Europarts sells Wahler.

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*My 91 240 seemed to have little heat and the temp needle was running 1/8"+ under the middle. I pulled it and went through the others I had around. I replaced with a Calistat 87 and seem to have better heat now - no surprise - and the needle is a smidgen above the middle. (I reuse used parts so, no, I didn't consider buying a new one