1998 Volkswagen GTI My car temperature rises up and the hig

About a couple weeks ago I noticed my car tempertaure was rising above the normal level and wouldn't go back down. Due to temperature being 100 degrees(I live in florida) I checked the high speed fan which wasn't working.I then replaced it and same thing happened. My mechanic suggested to have the fan control module replaced which I did but the temperature still rises up but the car doesn't overheat.A friend of mine stated it could be the engine oil that I haven't replaced in a while and I have added some oil a couple times because it was missing. Is it possible that the engine oil is overflown which would cause the car to overheat or could it be the sign of an engine head gasket issue?Should I perform an oil change and see what happens?Thank you so much for all the help you can provide, guys