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Has anyone come up with a way to confirm the oil temp besides testing the temp sender? Also is there anyway to confirm that the oil cooler is actually opening up and cooling the oil?
My temps run up to the 190's when I think the cooler should be keeping them in the 160's.
What causes the cooler bypass to open? Is the spring temp sensitive?
A friend with a new engine says his temp climbs fast to the 190's on takeoff and then slowly creeps up to above 200. There is no indication that the cooler has entered the system.

What was the outside temperature when the oil temp was 190F?
Why do you think the oil temp should be 160F?
What oil cooler by-pass valve did you install on your AeroVee? A standard AeroVee & oil cooler doesn't have an oil cooler bypass system. If the oil is flowing it's going through the oil cooler.
Are you perhaps thinking of the oil PRESSURE by-pass? That's the spring at the back end/bottom of the engine case. That will open and close in response to high oil pressure, doesn't care about temp.

I have a OneX with AeroVee just like you do. When the OAT is above 75F or so I can see oil temps in the 190F range. I've always been told by VW experts that that is a good thing, because higher temps help to eliminate water vapor from the oil.

According to the AeroVee manual the oil temp operating limitations are min=160F, max=240F