I have a 51 plate 318i that overheats after about 15 miles or so with no cabin heat. Water pump was changed before I bought the car and the radiator was stone cold so I suspected thermo. Had thermo changed by local garage today, cabin had heat and car was driving fine but after a couple of minutes started to overheat. Spoke to the mechanic and he replied without even a thought that it was the head gasket.
I've had no lose of power, no white smoke or creamy oil so I really don't believe it's the head gasket. I really think my issue is with the radiator as it never seems to heat up? I filled the coolant resivior with a bottle of Radweld plus and after 25 minutes took the car for a spin, car started to overheat but only to 3/4 mark and red light never came on.
So does it sound like a radiator issue or head gasket?