Does this alternator belt look worn?

[kiz17]

Hi all

Please see attached images. I’ve just done a 120 mile trip and 5-10 miles from home my battery warning light came on, but the car continued to run perfectly fine. I’ve done some research and the best case scenario is a worn alternator belt, worst case is a faulty alternator.

Before the battery warning light came on today, I have always noticed a pumping like sound when using the A/C & heating system. It’s a hard noise to explain but my car is always a lot noisier when using the A/C & heating system, as soon as I switch it off the noise goes instantly. I’m hoping this noise is because my belt is worn and would eradicate a potential faulty alternator. Or can a faulty alternator also cause problems to the A/C system?

Any help is massive appreciated as always!

Thanks for reading

 

[Chris-P]

When was the last time it was changed?

 

[kiz17]

Hi Chris

I’m not too sure to be honest, I bought the car in June and I can’t see any record of the belt being done in the service history.

It’s done 96k miles so I assume the belt is in need of a change?

 

[kiz17]

It might also be worth noting that the belt almost feels like fabric? Especially the centre of the belt

 

[aqibi2000]

Measure for 13.5V at the battery terminal with the engine started. Likely to be the alternator (belt may be worn but if the alternator is spinning then and not getting crica ~14V then it may need replacement)

 

[kiz17]

Thank you for the reply! A faulty alternator is not what I wanted to hear, I was hoping for a cheap £15 fix but of course it’s never that easy! I’ll go buy a multimeter and test for the voltage and pray it’s around 13.5-14v.

On the off chance, could it just be a faulty battery where it’s not charging properly?

 

[aqibi2000]

Thank you for the reply! A faulty alternator is not what I wanted to hear, I was hoping for a cheap £15 fix but of course it’s never that easy! I’ll go buy a multimeter and test for the voltage and pray it’s around 13.5-14v.

On the off chance, could it just be a faulty battery where it’s not charging properly?

Go to Nayanza or a battery place. Will take 5 seconds to plug in the meter and see if it's charging or not and also perform a battery test all FOC

 

[Retroman]

As above, with the engine running you should be getting 13.8 - 14.8 V as measured at the battery terminals. With the engine off, a good condition (and charged battery) should be showing 12.5 - 12.8 V. For these ribbed belts the true check for wear is the ribbed side - a worn belt will look very glazed and typically have horizontal cracks appearing. At 96K, I'd just change it.

 

[Retroman]

Forgot to mention that an old, glazed belt can "squeal" when the engine is under load - which denotes it is slipping. A weak tensioner can also cause this. Obviously a belt which is continually slipping will not be allowing the alternator to charge the battery properly and will also affect other items on the same circuit.

 

[aqibi2000]

Measure at battery terminal to see if issue is present, then at the alternator to rule out a bad ground cable.

 

[kiz17]

Thanks for the replies everyone. I’ve just fitted the new drive belt and got back from my testing:

The battery reads: 12.09v (I drove around 5 miles since the battery light coming on so I guess this is the reason it reads below spec)

With the engine running the battery reads: 11.90v

So it looks like the alternator has gone? Lucky me.

 

[aqibi2000]

Now: Measure the voltage at the output of the alternator with engine running. (Place black probe on the alternator metal body and the other on the output connection).

This will confirming there is an issue with the ground cable or alternator.

Btw don't drive around far with a depleting battery

Feedback the voltage reading

 

[kiz17]

Now: Measure the voltage at the output of the alternator with engine running. (Place black probe on the alternator metal body and the other on the output connection).

This will confirming there is an issue with the ground cable or alternator.

Btw don't drive around far with a depleting battery

Feedback the voltage reading

Thank you for helping with this. Shall I measure the voltage of the alternator with the engine running?

 

[kiz17]

Just down the testing with the engine on, it was jumping all over the place but it was most steady at 11.90, the highest it went was 12.55

 

[aqibi2000]

If your measurement at the alternator only went up to 12.5v then it needs replacement imo.second hand ones are cheap and easy to fit

 

[kiz17]

It was extremely sporadic though, it dropped to 3-6v then jumped to 11v, then dropped to 0.5v, then shot back up again.

I’m guessing just by how sporadic the readings were it shows the alternator is bad?

 

[ch1z64]

Forgot to mention that an old, glazed belt can "squeal" when the engine is under load - which denotes it is slipping. A weak tensioner can also cause this. Obviously a belt which is continually slipping will not be allowing the alternator to charge the battery properly and will also affect other items on the same circuit.

My battery is sitting around 11.8v cold and i am close to 100,000 and belt doesn't look like its been changed ( getting done Jan 19 ) so could this cause the low voltage in battery , done parasitic drain test but found nothing

 

[kiz17]

If it helps, changing the belt on my car this morning didn’t do anything to my battery readings. The belt done 96k miles though so needed changing anyway

 

[Retroman]

Often cars will struggle to start if the voltage drops below 12V
Approx. state of charge (voltage) figures
100% 12.7 - 13.2
75% 12.4
50% 12.2
25% 12.0
Discharged 0 - 11.9
I would suspect the alternator. As above, you may be lucky with a 2nd hand OE one. If buying new I would avoid the budget makes at ECP/GSF and instead buy one of the following 1) OE, 2) one made by the OE supplier or 3) Lucas. I have experienced several cheap, new aftermarket ones either to be noisy and/or fail at around 1-year old.

 

[kiz17]

Often cars will struggle to start if the voltage drops below 12V
Approx. state of charge (voltage) figures
100% 12.7 - 13.2
75% 12.4
50% 12.2
25% 12.0
Discharged 0 - 11.9
I would suspect the alternator. As above, you may be lucky with a 2nd hand OE one. If buying new I would avoid the budget makes at ECP/GSF and instead buy one of the following 1) OE, 2) one made by the OE supplier or 3) Lucas. I have experienced several cheap, new aftermarket ones either to be noisy and/or fail at around 1-year old.

Thanks man, it really does look like the alternator has gone. Shame because my previous A3 done 142k miles on the original alternator.

I bought an alternator earlier on today for collection tomorrow, after reading your exlerience with cheap ones I’m glad I went for the Lucas! £122 with discount so not too bad.

Also, after I fit the new alternator should the battery light go out? Or will it stay on until the battery gets fully charged?

 

[SootySport]

The light should go out when the alternator is fitted and battery over over 12v, nothing to reset to turn out the warning light.
With the engine running just make sure you see about 14volts across the battery terminals with yer voltmeter, that would indicate the alternator is charging as it should.
If the battery is 7years or more old, then you may need to change that well. With colder mornings coming up, any weakness in the battery will start to show.