Third way.
FYI, here's some info that was posted to this list by David Preston (who
in turn obtained this info from VDO) about 3 years ago. If you think your
sender is good and your gauge is inaccurate, you can check it like this:

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How To Check 300 degree Oil Temp Sender
Disconnect wire from sender.
Check the resistance between the terminal and ground

322 Ohms = 120 Degrees
105 Ohms = 180 Degrees
64 Ohms = 210 Degrees
35 Ohms = 250 Degrees
18 Ohms = 300 Degrees
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 Seems there  are only 2 ways to really know what temp your van is
running at.
One is  to install a better temp gauge and the other is to use an
Infrared