The Temp gauge on my '84 240 diesel reads consistantly about 2.5mm above the 9 o'clock position ( about halfway between 9:00 and the red zone )when the engine is at thermostat opening temp.
The engine is not hot at all .Temp. downright mild on hose going back to engine from radiator.
I put an external temp meter on the metal at the outlet hose and it was only reading 59 deg c.
On hot days with AC on climbing hills the gauge will get up to red zone and fan switch (87 deg. c ) will kick on about that point.
Radiator , thermostat, waterpump all new.
Gauge checked out OK as per green manual,
Just installed new sender.

Any ideas on what to do to that gauge to get it reading properly( other than taking a pair of pliers to the needle )?

Thanks-----------Robert