You're a technician? Then what I would suggest is getting a couple of the newest type thermistors, and hook them up so you know temp things are running at! Don't guess.
At todays prices they're really cheap, and you can get a small LCD module to recieve the output. Cheap peace of mind.....
Add.) The Logisys FP206 is a good controller - costs under $30.00, has LCD, and will display temps from thermistors and allow setting fan speeds.
I first saw this in the March issue of CPU magazine....