I am treating the oil cooling and the cylinder temperature as separate entities. Yes, the oil does keep engine temperatures down and stabilised but the rise in temperature on an air cooled cylinder is far quicker than the oil temperature rises so the fans won't be controlled by an in-place thermostat.
Hence the manual fan 'on' switch to enable instant access to cooling air.
I did toy with the idea of using a thermostat as you mentioned with its probe on the cylinder itself (tucked into the fins) but feel that is too hit and miss. These variable stats (I used to have a Kenlow one on my Caterham 7) are usually set-up with the probe set inside the top rad hose connection area. This is because the water will rise in temp at a constant rate so allowing the thermocouple probe to work well. The probe attached to a cylinder has too many variables to be consistent.
I need to check it out but think as the fans are only an additional safeguard that the manual system should be adequate. My workshop at present is sitting around the 0* to a minus figure so not easy to test.
My Lotus Esprit S3 had a OE thermostatic fan switch fitted as std but I still fitted a manual over-ride as these 'Otter' switches (named after the manufacturer) had a reputation for failing. The 'joke' in Esprit circles was the company called themselves 'Otter' as that's what all the engines they fitted their products to did. They just got 'otter!!!!!!
http://www.ebay.co.uk/itm/Radiator-OTTE ... 2c963be6d1
