That'* why I wasn't worried, because its behind the plate. And, remember its the old type of cap, where you line up the two tabs into the grooves, then twist, like a radiator cap. so I think it is less likely to fall off.
Actually, the car is going back tonight. :( His wife is coming to pick it up. I believe she is taking it to have the heater core fixed. (Didn't know anything was wrong with it) I'll recommend they look at the vapor line.
On a plus side, in exchange we'll be receiving his Lumina APV in exchange, so that works for me.