There may be some trapped air in the system, usually at the top of pipes, meaning that you can't get the right amout of coolant in. This means the engine will get hotter. I think there is a bleed screw on the radiator but will have to check.
Winter has passed so I'm picking up the old thread, I've noticed my oil temp is rising again, at the end of summer last year after all above posts I changed my coolant wich seemed to help but the temp outside wasn't so high anymore so I wasn't sure and I decided to let it rest because a bit more heat in winter is allways okay, now I notice the prob is still there, so, after I changed the coolant, if there was an air lock before, will it still be there? Or could it be the thermostat that isn't opening all the way or not opening fast enough? Cheers
Idd, prob is, it is not obvious what is going on, the watertemp goes up to 90° but in the meantime oil is rising too, water comes up to 90° rather fast but it is impossible to say if the oil is going up because of the water or the other way around