There are quite a few graphics cards stress test utilities out there. Run one and check GPU temp (shouldn't be much over 50C) and fan speed (around 2,000 rpm on full load). Also you will start seeing image corruption if there is a overheating problem.
Eva the cards come with a fan on it that it should be able to handle so if your son has not overclocked his card then it should be okay.....I have a Radeon 4870 on mine and I've actually underclocked mine because I still get quality performance but it's an extra 10 degrees saved on the card....now my card never goes above 70 degrees under full load it always stays in the 60's. I'm no expert but I've read that under full load the card doesn't want to be in the 70's at any point, but how accurate this is I've no idea.
Honestly I have no idea lol....also honestly I'm not sure it's wise to get involved with that kind of thing if you aren't sure what you're doing because you may end up in a worse situation with the best of intentions. I done it loads of times lol n wish I hadn't bothered.