The fan kicking in to cool your computer is normal. Not clear what you meant by haywire. Is it making a funny noise or something? If the fan is turning on and off periodically, this is normal.

Most computers can handle running at 100% CPU for extended periods of time. But laptops tend to be the exception, in their efforts to preserve battery power, they can sometimes oversize the cooling components and can overheat as mentioned in the recommended system requirements. If that does become a problem, you can use ThreadMaster. It let's you set the % of CPU you want to run at. The lower the %, the less work you can crunch, but the less heat is produced. You can learn more about ThreadMaster in the list of add-ons.