Guide Pulley or Alternator? 1986 300E
 

My 1986 300E has developed an intermittent noise sounding like a worn-out or dry bearing. The sound seems to come from the right side, either the alternator or the guide pulley. It seems to be loudest when it is first started. I put a screwdriver on the rear alternator bearing and felt some vibration although it could also be coming from the guide pulley bearing. Please note that the 300E has 280,000 miles on it and the guide pulley bearing is original. The alternator has about 60,000 miles on it, but it is regulating its voltage output and charging the battery just fine. I put a few drops of oil in the backside of the guide pulley bearing and the sound gradually went away over a minute or two. This could point to the pulley bearing or the fact that everything warmed up. I'm leaning toward replacing the guide pulley bearing. Any thoughts?

Thanks in advance for any input.

Brent Smith
Atlanta, GA
1986 300E
2003 530i
2003 Boxster S

Either it's the guide (idler) pulley, or the fan bearing is also a common high-mileage failure point. Just did mine earlier this year.

No conjecture needed...a four-dollar mechanic's stethoscope from Harbor Freight will definitively answer that question. ;)

Becareful of fan
I replaced my idler pully,now with sound I thinking,spring loaded pully

Check idler pulley, fan clutch bearing (they shear off and the fan clutch destroys your radiator + more -- check for ANY wobbling forward/backward) and check tensioner shock where it connects to the head.