If you have a vehicle that runs hot, then the summer months can be brutal. Because the engine is already hot from sitting in the sun, it doesn't take much to overheat if you have a problem.
There is no way to predict what the problem is without looking at the vehicle. You will need to take the vehicle to a certified shop or dealership to get a proper diagnosis.
The thermostat could be stuck closed, the radiator could be clogged, the coolant could be low, or the radiator fans may not be working properly. These would be the things I would check first and then go from there. Good luck.
〉 Answered on Jul 25th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines