Hello Mr Courtney,the only way that it would be safe to buy this car now, knowing what you know is to let them give you the car, you hold the money and drive it for a month. If it doesn't have any overheating or cooling system problems in that time,it would be pretty safe to pay them. If you pay for it now, then start to have cooling system problems in a week or so, its only going to become a hassle between you and the dealer.I know they probably won't want to do this,but it would be the only way to protect yourself. It could have been an air pocket,or a thermostat,but it could have overheated before and have a blown head gasket or worse. Parts and repairs to that car are expensive,so please be careful.I hope this will help you to make a good decision,Jerry.