Here's the setup actually running.

One thing that I discovered is that the copper coils around the grease filter are not up to temperature until several miles after the car's temperature gauge shows 190 degrees. Then I'm sure it takes some time for the grease filter itself to heat up. In fact, the copper coils never topped 160, and when running below 2000rpm, the coil temperature drops to as low as 110 (ambient temperature was about 48). This surprised me... I expected those coils to reach about 190 at about the same time the car's temperature gauge did. I'm afraid this is showing me that I've been switching to VO before it is heated up well enough and that the grease filter *never does* heat up to an operating temperature of 170 or more.

I'm going to try putting the sensor on the injector pump next. Since that's mounted on the engine, I'm guessing that it will be warmed up more quickly than my external grease filter. If the injector pump is warmed up, I think that will suffice (as long as the grease isn't stone cold), because the return line T's back into the incoming fuel line. This means that most of the fuel that gets injected has gone around that loop probably several times -- becoming warmer with every pass.

I'll post my results when I have them.