To me this sounds like a stupid question as I'm very familiar with desktops and not so much with laptops. But is the CPU/heatsink fan suppose to run all the time? I noticed that mine doesn't start when I turn the laptop on. It does go on from time to time and I was wondering if it was thermally activated.
I have had a few freeze ups and I suspect the CPU turns itself off to protect itself.
Have you checked the heatsink for dust/grime buildup? I use a canned air product to clean fans once a year or more. It contains solvents that evaporate quickly. As for the cpu fan, it probably activates only when needed to conserve battery life. Find a good laptop cooler with fans that sits underneath. They are only about $15 or less with rebate.
Yes I've cleaned it out with a can of air. I do it every 2-3 of months with all my comps. I've ran a stress test on it and the max temp was 64C, the fan comes on and it drops to about 54C. This happened several times. Idle temp was 40C. I'm thinking it is thermally activated, even though I'd like cooler temps.
64c won't hurt the processor. The freeze ups could be caused by the northbridge chipset on your motherboard. They often come with cheap aluminum heatsinks or none. You can buy an aftermarket heatsink with or without fan and press it on. Most come with plastic clips. But removing the old one may require you to remove the motherboard. So proceed with caution.