Check the low and high speed fan relays for the radiator and condenser fans. Check your radiator cap, the system requires a 1.1 bar cap. The oil is not particularly relevant. A leaking head gasket is a separate issue to be diagnosed correctly and thoroughly before replacement.
You might also have a leak, air in the system, or a partially stuck thermostat valve. Check that the cooling fans turn on and run at the right speed and supply voltage when the coolant temp is 100°C.
Pull the live data stream with the help of a competent mechanic and observe before randomly throwing scrapyard parts at the car and hoping it solves the problem.
