I experimented with an oil temperature sensor instead of the oil dipstick but the device was broken over the time and I had oil leakage problems. Now I replaced it by a temperature sensor in an additional flange between oil filter and engine block. I used a kit by Raid Automotive Concepts. It has a 3/4 unf thread for conventional W718/2 Alfa/FIAT oil filter cartridges and a conventional oil filter mounting pedestal. The anodized aluminum extra flange is able to accept a small sensor with 1/8 inch 27 NPT conical thread.
Sensor specs of the new oil filter sensor: 1,8 kOhm @ 20°C - 150 Ohm @ 100°C