Voltage fluctuation

[ted944]

I have seen some voltage fluctuation recently and not sure if it's normal for the 944 or something wrong.

My daily commute is about 10 miles each way with 6 miles highway and 4 miles local with some traffic lights.

In the morning when the car is cold, I'd see the voltage on the voltmeter is above 12 and sometimes close to 13. Only when driving at the highway speed with 3500 RPM, the voltage is slightly higher.

But in the afternoon, the voltage is normally lower, sometimes close to 12. The highway driving does not seem to change the voltage much. And once I get on to the local road in the stop and go condition, the voltage can drop below 12. The next morning the voltage would be a little higher.

The battery is brand new Bosch installed few month ago, there is no radio or other electrical things running besides the car's own power train. The overall average voltage seems to be getting lower and lower than when the fresh batter was installed.

Is this normal to the 944? Or the charging is getting weak? Any idea?

Thanks

[mytrplseven]

Check the Alternator drive belt tension. It could be slipping and be the root of your problem. It happened to me, too. If that doesn't solve your issue you may have an issue with the exciter wire going to the alternator or the alternator itself or voltage regulator on the back of the alternator. There are some other more exotic issues within the guage cluster that I won't go into right now, so try the basics first.

[ted944]

Made some measurements to the battery:

When the engine is shut off, the voltage is 12.54, while the gauge shows 12.

When the engine is idling, the voltage is 13.34, while the gauge shows a tiny bit above 12.

Checked the belt tension, it is tight.

It seems the charging system is working, so maybe the gauge is having some issues.

Thanks for the suggestions.

[Gawernator]

When is the last time you cleaned your grounds? I'd try that first. Then I would clean all the gauge's connections. That fixed my "broken" volt gauge.