Possible alternator problem, advice needed.

[chris-y]

Hello all. Firstly, I apologise, I bought my VXR8 yesterday and would normally have introduced myself first but I have a problem I need to ask for help with.

The journey home from buying the car was 330 miles, the dash board voltmeter read about 14v as you would expect for the first 200 miles. Then I noticed that it had dropped to 13v.
To cut a long story short its usually reading about 13v now, occassionally popping up to 14, sometimes less that 13. I used a digital multimeter between the positive post under the bonnet and chassis ground and got 14v, then seconds later 12.8v, which it stayed at since.

My guess is that the alternator is failing due to normal wear and tear (car has done 109K miles), my questions are -

Would you agree, or is there something else I should be checking?

Where is best to source an alternator, does anyone have a part number, I wondered if its a common item readily available, or special to our cars.

Thanks for any help you can give, I'll introduce myself better later with a pic of the car.

[vxr2010]

I will say what i’m aware of , the vxr8 charging voltage varies depending on the battery , the 12.? seemed a bit low , there was an ecu upgrade that sorted a charging issue , i’m assuming no cel lights coming on and i assume your battery is ok and not on its way out , my forester same sort of charging system , first start of the day is around 14.2/5 volts then as the drive goes on it goes down to 13.5/7 of so but apparently that’s fairly normal , i would put it into engeneering mode , hold left steering wheel toggle down and keep an eye on voltage plus battery charge , are earth wires ok i always put an extra one on , if it is going south there is a place in borehamwood herts called unit exchange give him a call , it can be posted to them , a rebuild is around normally 80£ to 100 depending on parts , no cel is a good thing if that’s on and not charging you definitely have issues but as above could stem from older battery

[stevieturbo]

You could buy a new one from the US or Aus...

But any local alternator shop should be able to get the parts to repairs your own.

But if voltage is dropping, yes it needs looked at.

[chris-y]

Thanks for the replies so far

I didnt know about engineering mode, a quick google search has educated me on that one, I'll have a play later and report back.

There are no warning lights on or any messages on the dash when this happens, or any other time.



Jumping ahead a bit here, is the alternator reasonably easy to change from the top, I dont have access to a lift or ramps. Any tips welcome.

[vxr2010]

if it’s the same as the monaro it’s do able but a bit of a faff , belts off to give you as much room a few bolts three i think which can get stuck , unscrew plugs/wires as they are two from memory then a bit of a fiddle and the right angle to get it out from top of engine , monaro it comes out from the top of the engine vxr8 i assume the same , it’s difficult to say if your alternator is going for certain engineering mode will help , as above how old is your battery ?

[Davep24]

A lot of modern car alternators have excitation on demand i.e it only delivers power when the ecu deems necessary, it something to do with batteries not liking being constantly charged. The 14v you saw is the battery being charged, this will drop off as the battery nears full charge.

I would just keep an eye on it, if you are not getting and warnings or problems then theres no point in spending money if it doesn't need it

[chris-y]

Thanks for the replies again, much appreciated.

Engineering mode confirmed low voltage, as low as 12.6.

The charge/excitation on demand is new to me but makes sense, and would explain why sometimes its 14v, and so definitely can deliver the expected voltage (no way to know current) and sometimes its lower, quite possibly when I'm seeing low voltage its intentional low excitation by the ECU.

I had a few messages with the previous owner last night who is very knowledgeable and helpful, he suggested charge the battery overnight just to make sure its charged as its been standing around a bit, then dont worry about it if the car isnt displaying any warnings.

I've charged the battery last night, today started at 14v, for about 5 miles then back to 13v, so maybe there isnt anything wrong.
I've heard extra gauges called paranoia gauges, know I know why, if it didnt exist I wouldnt be concerned.


I dont know how old the battery is but I'm aware that these cars are sensitive to battery condition from reading posts, if I had reason to suspect it I'd change it and consider it money well spent. Vauxhall trade club battery prices are good so it wont hurt too much.
I'll see if I can find out how old it is.

Thanks again.

[H5V VE]

Hi

Don't forget that these cars have very specific battery types and charging cycles - it's a silver one so make sure you have or get the right type - Bosch Silver seems quite popular

[vxr2010]

When my monaro alternator stopped working it was cel and other bits having a moment so it was very obvious it was at fault which i expect the r8 would be the same , the specific battery as above is not wrong but i personally have just put any suitable one on

[chris-y]

I wondered if it would be a specific type of battery after learning about the more complex charging system, an old fashioned lead acid battery would be happy with 14v at all times but my limited understanding is that some of the modern batteries need very specific charging.

Its changed its behaviour now, and I'd say that whats happening is quite unlikely to be a fault alternator and more likely to be the ECU controlled on demand charging.

I went out in the dark last night and it showed 14v throughout, which makes sense, if it decided demand was higher and it should excite the windings to provide higher output.
Oddly though today during daylight its been 14.5v all day which I didnt expect, it seems a bit high to me when thinking about normal older cars.

I think the answer though is that the ECU is probably making the decisions and the gauge is a bit pointless because there isnt an OK or No good reading, it depends on whats required at the time to maintain the battery.

I think I might be best to take the previous owners advice and dont worry unless the dash displays a fault, which it never has so far.


Good advice on the battery though, having read about these cars sensitivity to battery health its something I would change as prevention when the cash is available. I know not to just buy one that fits.

[chris-y]

While we are on the subject of batteries, the Halfords website recommends this one -

https://www.halfords.com/motoring/bulbs-blades-bat...


The price is reasonable, cranking amps are high and I have a trade card so would get a bit of discount.

Not that I need to buy one immediately but does this look a good choice to those of you with more knowledge than me?

I also thought about trying the Vauxhall main dealer because batteries at trade club prices are usually surprisingly cheap, any thoughts, has anyone tried them?


I know I'm off on a tangent here but I'm keen to learn about the cars and be prepared for whatever comes up.

[vxr2010]

The engineering mode tells you from memory battery charge or life ? , it’s been a while but i think i changed mine when it was at 30 per cent charge/life , so in basic terms it was not holding charge very well , i was having no car issues but clearly battery was on the way out , they seem to work then just go rather than slowly go as i found out on my ute

[SteveMJ]

I haven't studied all the replies in detail.

But having had my VXR8 for 9 years, the indicated charging voltage has always been all over the place.

I used to drive an hour each way to work and it rarely showed 100% charge (in engineering mode). I had the first alternator die after about 75k miles, there was a warning that flashed up on the instrument panel.

I personally would not be concerned about your battery or alternator based on what I read in your first posting. Mine drops to ~13.2 volts, then some time later increases to 14+ volts. All for no reason apparent to me.

Steve

[chris-y]

I'm not worrying about it at all now, its clearly just charge on demand. At least I've learned something about the car with your input.

I havent been able to get battery life/charge to display in engineering mode though, just voltage, I'll have another go tomorrow, but in reality I dont think there is a concern at the minute.

[SteveMJ]

Does this help:

[chris-y]

Thats fantastic info, it explains everything.

Thanks for that, much appreciated.