We had a problem at a company I used to work for with drives overheating. Some things I found that help the problem...
1. Space the drives apart allowing for airflow.
2. Add extra fans to the case.
3. Make sure cables aren't blocking airflow.
4. Make sure you use all 4 screws to mount the drive. (most people are too lazy to or just don't think it is necessary) The most import thing this accomplishes is allowing the case to act as a heatsink. Also helps reduce any vibrations that could cause damage.
In the end we just got 5 1/4" drive bay enclosures that had 2 built in fans. Something like this... http://www.newegg.com/Product/Product.aspx?Item=N82E16835119062