IIRC, the Regina FI system cars use a thermal switch in the radiator right side tank to trigger the fan. Bosch LH 2.4 triggered the fan from the ECU, and had no rad switch. I had a 940 and the fan only started up when the engine got quite hot, or the A/C was cycling.

So, I see three possibilities:

- the engine is indeed running hot, so replace thermostat and see if that does it

- the fan switch in the rad is triggering at too low a temp - replace it

- the A/C pressure monitoring (pressostat) is triggering the fan too soon. Hope that isn't the case, as they are a pain to swap out. (If you are not using A/C when your fan issue occurs the pressostat is not the problem.)

As for 740 temperature gauges, the one I have in my parts bin has a rather sophisticated looking printed circuit board on the back side, with several transistors, diodes, resistors and capacitors and an 8-pin integrated circuit. More than is needed to simply provide a smooth gauge response to the sender as the engine temperature varies.

I once attached an ohmmeter to the output terminals of the gauge temp sender on the engine of my 940 and it was interesting to see the resistance drop quickly as the engine warmed up, stabilize as I cruised down the highway, then drop further at a stoplight. With everything connected back up, I never saw the gauge move once warmed up, so I conclude that there is some damping going on in the "normal" range of engine temperatures, just like the later 240's.

The temp gauge on my S90 (rebadged 960) is driven from the ECU, but I believe all 700's/940's used a separate sender on the engine. Certainly my 1994 940 did.
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Bob: Son's XC70, my 83 244DL, 89 745 (Chev LT-1 V8), 98 S90, and XC60. Also '77 MGB and some old motorcycles