I recently bought a 92 300E with 117k mi. The car runs great, but I've got a small problem with the aux fans. When I first start up the car from cold, they both come on full speed intermittently, sometimes for just a second or two, sometimes longer, occasionally for 10 to 15 minutes or so while driving. The coolant temp never goes over 80 even when they're not running. What's the most likely culprit? Is there a simple check and/or fix for this?

What is the proper operation of the two fans? When should each come on and at what speed?

Thanks