Help with M52tüb28

[e39life]

I live in south florida and it gets so hot... the expansion tank exploded and radiator started leaking one day so i canged all the hoses, expansion tank and the radiator. Everything works fine now but when i idle, red oil light come up and only when engine is warm and car is stopped. Any idea what this could be? I changed the oil not that long ago (liquimoly 5w40 & mann ) im planning on changing the oil anyways just because , is the oil i used not good? Thats what was recommended at a local shop