I don't know about "safe". Mine boils over at 240* and sounds really bad when it does it. Like you expect something to explode any second. 220 may not be too high but it's too close to the boiling point for my comfort level. When the needle reaches 210 my eyes are pretty much glued to the gauge till it comes back under. Doesn't happen often but sometimes on a hot day, idleing in traffic for 45mins or so, she will creep into the no no zone. Outside air temps definitely affect radiator temps. 40* air being sucked through has alot more cooling effect than 100* air over the surface of rad tubes.