Headlight problem

Tiny
DJPORTER
  • MEMBER
  • 1993 GEO PRIZM
  • 193,000 MILES
I have a 1993 Geo prizm lsi 1.6l with an electrical problem. When cold, everything is fine, after car warms up, voltage drops and headlights dim. It has a new battery and alternator tested fine, albeit in cold state. Terminals are clean and no loose connections. What I find odd is when the problem presents itself, the voltage will drop to about 11.5 and stay there. Any ideas? Is it alternator failing or do I need to look elsewhere?
Tuesday, December 20th, 2011 AT 1:49 AM

4 Replies

Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
Replace the alternator 11.5 is way to low.
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Tuesday, December 20th, 2011 AT 2:16 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Check the crank pulley if equipped with harmonic balancer. Ensure the alternator belt is adjusted correctly.
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Tuesday, December 20th, 2011 AT 4:11 PM
Tiny
DJPORTER
  • MEMBER
  • 1 POST
Interesting, problem surfaced after I had replaced the harmonic balancer. It was a used part pulled off a car. What should I check for as far as that is concerened? As far as alternator belt, it doesn't seem loose. Can it being too tight cause a problem?
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Wednesday, December 21st, 2011 AT 2:55 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Tight would not cause the problem described but it might emit a humming noise.

The outer ring of the crank pulley could be freewheeling over the inner pulley if the harmonic balancer is bad.

Use liquid paper to draw a line across the face of the crank pulley. Run the engine and after a few minutes, stop engine and if the line is out of alignment, the harmonic balencer is bad causing the non charging.
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Wednesday, December 21st, 2011 AT 2:12 PM

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