Hello,

My voltage has been dropping to 12.8-13.0 volts when my radiator fan and headlights are on at the same time. When both of these are not on, the battery is running 14.0 volts.

So does this mean there is a problem with the alternator?

 

It seems fine. Headlights draw about 10A/pair and radiator fans can draw 15-30A.
Add another 15A if you're running climate control fan on full. Having all those on at once pretty much puts alternator to the limit at idle speed.

Those big fans and rear window defroster are perhaps the most powerful sustained power your alternator has to provide. Alternators are not designed to produce full rated output.

When you blip the throttle a bit from idle its not uncommon on many cars to have the voltage bump up enough to produce a audible difference in blower fan speed.

you're in trouble if battery warning light comes on though. that light tells you that current is flowing out of battery.

 

Ditto the above^^^ kind of, a batt. light indicates alt. is not charging.

I would redo, [clean] the main grounds, batt. post and cable clamp, batt. to chassis ground and chassis to engine ground, DO NOT just eyeball the connections, disconnect them. clean both contact surfaces, reconnect making sure the bolt/nuts are tight.

Grounding problems are the most common "electrical" problems, by far, that come to our shop. 94

 

Thanks for the information guys. One last question.

The battery durng a cold start should be at least 12 volts, correct? If it isn't at 12 volts then there is a problem with the battery, correct?

I have an optima battery that reads 11.8 volts after its been sitting for a while.

 

You have to check your batter under a load to determine if its bad.
Crank your engine over with your volt meter attached to the battery, if voltage drops more than 2volts you have a bad cell in the battery.

 

I took the efi fuse out so i could crank the engine continuously and I got abou 11.4 volts. So it seems like the battery is fine. Thanks for the help. Good learning experience.

 

After you let the car rest over night the battery should read 12.6+ v

If it isn't, you might have a drain like incorrectly installed accessories or something stuck on (i.e defective or sheared off trunk lid switch causing trunk light to remain on all the time)

If that is not the case, the battery is bad.

For effective starter operation the voltage at battery terminals should not fall below 9.6v.
Healthy voltage at battery but poor start means connection issues or brushes or more likely, contacts within starter/solenoid.

 

I did just do a Voltage drop test on the positive and negative side of the circut. of the alternator.

Negative side: 0.05 volts

Positive Side: 0.15-.2 volts

Now I have read that anything above 0.1 volts is bad. So can I assume there is an issue maybe with the power wire between alternator and battery?

 

It wouldn't hurt to remove the connection, clean it up with steel bristled wire brush, add a drop of oil and put it back together. If you find bad corrosion you might actually have to grind off the corrosion with a Dremel.