I have had both thermostat and head gasket go over the years. If the oil is frothy it might be gasket. The two symptoms are similar unless you look for water in the oil (froth/emulsifying) or bubbles in the radiator (run without the radiator cap on tickover till warm) bubbles can be very small. I have never had a fan fail on me but the fan should be cutting in and out on tickover and especially if you reach the overheating point.

Modern engines don't always have radiator caps as we know it. Didn't Spaw say he had worked a lot in repair shops over the years? He MUST have an opinion here.