So My temp gauge started randomly spiking up to almost in the red zone, so I did the compensation board bypass, no more spiking, but the gauge reads high all the time, and reading higher.
3 row radiator clean, new tropical fan clutch, low temp fan switch for aux electric fan, new water pump, new thermostat, volvo dealer, new sending unit, coolant air bled off.
Here's the wierd part, it's 76 deg f outside, the gauge is reading a little less than 1/8 inch below the red zone, but when measuring the actual temp of the water comming out of the thermostat to the engine, it's only around 150 deg f, and the water going back into the water pump is only 97 deg f, comfortable to hold the hose.
I have checked all the sending unit, wiring, gauge as per the green manual, and everything checks out ok., but the darn thing persists in reading high.
I'm at witts end on this one.
Any thoughts?

Thanks-------------Robert
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '82 Mercedes 300SD for sale