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 have encountered thermostats with and without the arrow. No apparent reason for the arrow that I can see. For sure, I would abide by the FSM direction to point the arrow up.

Some thermostats have a vent which need to be at the top. But the 616/617 thermostats that I have seen with the arrow had no obvious vent.

I just went through this. My car ran at 80 when at fully warm operating temperature. It ran to cool with the heater on the heater sucked. I got a new Behr thermostat and did a coolant flush. Now it runs at 95 and its cold outside. The heater works great too. I thought I had installed the thermostat backwards so I checked and it was installed right. The Top hose gets hot and I burped the system and its got full water flow in the upper hose. It has not hit 100 yet but come close. I will see what it does in the summer in stop and go. until then I will quit worrying about it.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

I too have recently installed a new Behr thermostat in my 85SD. The temp gauge reads 90* at all speeds when warmed up. The old one was at 80* on street driving and up to 90* on the interstate.

The infared shows cooler. I forgot the exact measurement but am wondering if there is a way to test the sender. I've found specs for other vehicles I've owned - usually a chart xxx ohms at yyy temp.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Owned my 240D since new and have had two or three thermostats in it. They have all read about 85° and are pretty rock solid at that number no matter the conditions. Under the worst conditions it may go to about 90°, but that's it. Use MB fluid or Zerex, a bottle of Water Wetter and change it every three years.

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

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.