Hi mate, when the weather and engine is cold your oil pressure should be higher but if the screen on the bottom of the oil pick up pipe which feeds the oil pump is getting blocked the thick cold oil in the sump will find it harder to get to the oil pump. Unfortunately this is not an easy one to solve without taking the sump off and cleaning the screen, you could try flushing oil but I am not a big fan off this method (just my opinion). As suggested by Davyonthemove you could try a lighter grade oil as this may help, it could also just be a faulty oil pressure switch which sends the signal to the oil light. I don't think there is anything too serious at the moment but keep an eye on it in case it gets worse but if you are still worried replacing the oil pressure switch with an oil pressure guage adapter would show you exactly what pressure you have in the system when cold and when hot, I keep one in my tool kit but not many mechanics bother these days.Regards .... Pete. Thanks Pete Have a pressure switch ordered, hopefully will solve the problem Regards Techie