451 overheating, even when moving

unless the previous owner was running race coolant, we test drove for nearly an hour before I bought it and there was no indication that overheating would be an issue.
So generally when racing you're running straight water so if you do have any issues you're not covering the track in antifreeze. I know I missed the part about the car being driven for nearly an hour before with no over heating issues.... Makes me wonder what changed in that time. If things where working before and not they are not, something has changed.