MacBook :: It Suddenly Running Very Hot At Idle

I'm posting this on behalf of my father. He has a 2008 white macbook which has recently started running quite hot (160-180+F), even at idle. It has the latest version of 10.7 installed. He has an external HD with his previous copy of 10.6 and it exhibits the same behavior when booted from that system.He bugs me whenever he has computer problems told me that his MacBook had started randomly shutting down with no warning. I had similar trouble with a MacBook Pro and it turned out to be a faulty battery, so we got him a new battery, figuring it couldn't hurt to have a fresh one with a 4 year old computer. it didn't solve the problem at all.

Later he said that he noticed the computer felt hot, so he decided to run a small fan blowing across the computer while it was on his desk, and that stopped the random shutdowns. So I thought, OK, this is an overheating issue. Maybe the fan isn't working properly, it's full of dust, something is hogging the CPU all the time, etc. 

The next time I was at his place I had him install fan control and a temperature meter. We noticed right away that the thing was running really hot. It was at 160-180F while at idle. He had menu meters installed, after a reboot we could see that the processor was sitting at 2-5% load. Not only did the sensors report the high temperate, but I could feel that the bottom of the case was very hot.We decided to open up the case and see if there was dust clogging things up, etc. There was some, but nothing clogging vents or anything. We blew it out nice and clean with compressed air anyway and put it back together. I even turned it on while we had it open so I cold see that the fan was actually spinning, and it was.