Have you seen a Wahler 616/617 thermostat with an arrow?

What's your thoughts on orientation?

I'm fairly sure I have the Wahler and there is no mark...........??

i can't answer that, as i don't recall seeing a Wahler thermostat in the few/half dozen i have pulled or have seen. i do have a thermostat housing assembly to dismantle. if there's a Wahler in there, i will report my findings.

edit: disassembled the thermostat housing: Wahler thermostat. no arrow or orientation mark.
the thermostat i pictured above is an MB stamped unit. the part that closes against the housing is a flat circular disc. the same part on the Wahler is a disc with a curled up edge. the o.d of that disc on the Wahler is .2mm smaller than the MB part. it also looks as if the Wahler unit, over time, wore an unequal (only worn about 1/2 way around the seating area) groove in the thermostat housing, like that disc opened in a cockeyed position.

I believe that the gauge can be faulty... both of my cars have a dancing temp gauge... i have checked both with the infrared gun and they are both running right around 85

Similar situation. My brother's 85 123 running hot. He had a near overheating/low coolant situation in June. His mechanic replaced the water pump and thermostat and ever since then, it has run 90 to 100. Today we replaced the radiator due to a leak, still running hotter than historically but no leak.

Questions:
Has anyone pulled out the T-stat completely and run the car for a while to see what it's native operating temperature is?
Has 80 always been the initial point of opening with 94 full open, even in the "old" design t-stats that seemed to keep the car closer to 80 all the time? In other words has 80 ALWAYS meant the point of first opening?

Lastly, I'm suspicious that these T-stats are purposely making our engines run hotter for emissions reasons and they haven't disclosed that fact to us.

This is all speculative. The guys that have used alternate measuring devices know way more about those methods than I do. Perhaps this explains everything. What I don't know is why a thermostat change would [I]suddenly[I] make the temp gauges be out of calibration.

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Running with no T-stat wouldn't give a proper 'native' reading as the stat also provides a required flow restriction. To properly find what the engine would run at without a thermostat requires a flow restrictor of the proper size to be put in place (kinda a big washer). We didn't run thermostats in race cars but we still had to have the flow restrictors.

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Eric, CPO, Submarines, retired.
Here's a sig line...
Mine: '68 Corvette LS1/4L65E, 83 240D, 2000 GMC 4x4, 08 FLSTC Anniv
Hers: '72 Corvette 454/4spd, '99 MB SLK, '93 Metro vert, 78 240D, '92 Silverado, '65 Fjord Rustang, '59 Fjord Fairlane, '17 Slingshot.

My 84 300D runs 95c all day. Creeps up to 100 idling but never goes over that. I'd change the thermostat but I prefer running 95-100 over 80. Assuming (as mentioned previously) that our gauges are precise.

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1984 300D w/ 370k mi. daily driver
1994 7.3 idi non-turbo 180k mi.