advice on installing aftermarket aux. fan on my 89 300e
 

I'm thinking of putting a higher power aux. fan in my 89 300e. I live in Phoenix and the car always runs hot during the summer. Can anyone tell me how to go about finding out what the stock fan is rated at. I think they call it the CMF rating.
Any advice on this subject would be helpful. I'm not sure if it's common for mercedes to run hot like mine does, or if putting a higher output fan is the best way to handle the problem