Voltage gauge fluctuates, but alternator checks out

Jordan_Glad
Sun, 08 Apr 2018 22:21:10 +0000
Maintenance/Repairs

I have a 1994 GMC safari van, when the cars on the voltmeter fluctuates between 13 an 18ish, and I hear a rhythmic wirrring sound that matches the movement of the needle and of course the pulsing lights. This happens if either everything is on or everything is off (lights, heater, stereo) but after driving for a while the meter sits calmly at 14 volts. I got the alternator bench tested 8 times at auto zone, passed everytime. Is there something else that’s perhaps disrupting the speed of the belt, creating the wirrring sound, and since the belt is changing speed, changes the alternator output?

18 posts - 8 participants