Sounds simple but make sure the t.stat isn't installed upside down (comments on "changing the orientation"...did you spin it or check for it being right side up?)...I would imagine that would cause a closed condition rather than open. It has been the culprit to more than one thermostat thread in recent memory on here...

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

I have to say that I could not find any markings on the 'stat to indicate orientation with respect to the housing.

I fail to grasp why a symmetric piece of equipment such as a thermostat would require any specific orientation.............??

I am quite confident that it is not installed backwards............

the thermostats i've either pulled out of parts cars, found in my car (cheap chinese POS that was in the center console), or have bought (Behr) have had an alignment mark, except the Wahler i just removed (see post further down the page).
not sure why it is important either, but "the book" specifies an orientation, therefore i will abide by their request.
perhaps is has something to do with the way the water flows through the "arch" of the thermostat when the t-stat is partially open? or just maybe for coolant flow in general? <---pure speculation

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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.

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.