There are both electrical and Bourdon tube type oil temperature indicating systems installed on the E powered "real" Bonanzas. Which do you have??
A very simple way to check the operational accuarcy of thecockpit gauge is to obtain a long stem thermometer and after flying and engine shutdown insert the thermometer stem into the oil tank and compare the cockpit indicated temperature with the tank reading.
The oil temperature indicated on the cockpit gauge will be the same (for all practical purposes) as the oil tank temperature if the cockpit system is indicating correctly.
A suitable thermometer is available is from W.W. Grainger Co, their PN-1NFX or 1NGD9, 1% accuracy, 0-250F range, stem 12" long, both about $50.
I suppose that after doing the oil tank one could wipe off the stem and use it on the turkey next Thanksgiving.
Regards, Lew Gage