On hot days with the a/c on, doing 80 on highway temp gauge goes all the way up to the "O" on normal. It will also happen driving hard around town, lower speed but high rpm's. I've search and read many posts, but still not sure if this is a problem or not. I've changed the stat with a stock one from Ford, had a shop check rad,fan and if it comes on when it should, replace the air deflector that was missing, tried additives, but still today it was way up there. If it stays in the normal range,is this safe and good for the car? Any input would be appricated, thanks.