10 replies to this topic

[jayartibee]

Might some kind person run their diagnostic eye down this?

 

• poor starting - battery appeared knackered - would not hold much charge even when left on external charger for 2 hours @ 3 amps
• once jump-started, electrics were healthy, headlights bright, all electrics on
• new battery fitted
• charging light now on - alternator service message - battery voltage 12.3V (engine off) - 11.5V (engine on)

 

Could the alternator really have gone down at the same time as the battery? 

[northpole]

It probably is the reason why the battery died in the first place...

And thinking back on your hot start issues, this might have been the cause, not often that this shows up but deffo one that could have caused the hard starts...

Now for your info an alternator doesn't all of a sudden die it is a slow process so it gradually got worse until it stopped working.

[gerrywac]

It probably is the reason why the battery died in the first place...

And thinking back on your hot start issues, this might have been the cause, not often that this shows up but deffo one that could have caused the hard starts...

Now for your info an alternator doesn't all of a sudden die it is a slow process so it gradually got worse until it stopped working.

Hi Northpole, I'd have to disagree on the alternator failure. My alternator suddenly failed one morning last year just before Covid lockdown last year, light wouldnt extinguish after a start.
When the garages closed and I was at home I was left to sort it myself.
Long story short the brush/voltage regulator oack failed, brushes ok as was the rest of the alternator.
Got a new pack and fitted it, alternator back in the car and back to normal.

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[jayartibee]

But with the weak battery, when it was jump-started, there was plenty of oomph from the alternator? Headlights on full etc?

[gerrywac]

Poor starting after days of standing, and particularly in cold winter weather when the cold engine, especially diesel, needs the maximum current is a sure sign of a battery past its best and on the way out.
Once jump started the demands on the battery are much lower and whilst things may appear normal but thats not the case if starting after a few days is a problem.
A fully charged battery measured an hour or so after disconnection should read 12.6-12.8v,
12.3v off the charger isnt fully charged and if the batterys past its best may not have the oomph for starting
The alternator light coming on may be coincidental, it indicates its not charging correctly and your low voltage engine running confirms the point, tickover it should be 13.8v ish and maybe 14.2v with revs.

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[northpole]

Hi Northpole, I'd have to disagree on the alternator failure. My alternator suddenly failed one morning last year just before Covid lockdown last year, light wouldnt extinguish after a start.
When the garages closed and I was at home I was left to sort it myself.
Long story short the brush/voltage regulator oack failed, brushes ok as was the rest of the alternator.
Got a new pack and fitted it, alternator back in the car and back to normal.

Sent from my HRY-LX1T using Tapatalk

That isn't how they normally go... yours was just a freak accident... it normally is the bushes that give up the ghost... and they go slowly.

That said he had hot start problems before so it is possible that his alternator has been acting up for a long time before it finally gave up.

[gerrywac]

That isn't how they normally go... yours was just a freak accident... it normally is the bushes that give up the ghost... and they go slowly.

That said he had hot start problems before so it is possible that his alternator has been acting up for a long time before it finally gave up.

Yes I'd agree its almost always wearing and finally worn brushes so the alternator can be below par before the brushes don't connect at all and the light comes on. I sas hoping mine eould be just that.
Mines a Mk5 and the Bosch alternator has the brushes and regulator in one unit held on with a couple of screws. Original near 13yo 94k. Aftef removal checked andthe brushes were fine including length, commutator ok but examining the case there was a bulge and split with scorching suggesting fried regulator. Not sure if the 4 is the same.

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[gerrywac]

But with the weak battery, when it was jump-started, there was plenty of oomph from the alternator? Headlights on full etc?

With a failung or undercharged battery the voltage gets pulled way down and may not work the electronics never mind enough to start. With no or fairly low load the voltage springs back so once started even with an underperforming alternator things may seem normal

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[jayartibee]

All very odd - it seems the alternator went down at exactly the same moment the battery was replaced. Just weird.

 

Is there a guide anywhere - or even advice - on V5 alternator replacement - it's very crowded...

[northpole]

save this link as a favourite 

[jayartibee]

All very odd - it seems the alternator went down at exactly the same moment the battery was replaced. Just weird.

 

Is there a guide anywhere - or even advice - on V5 alternator replacement - it's very crowded...

I didn't do it myself - my local indy replaced with a brand new alternator for £266 all-in. Really can't complain

 

And the old alternator was effectively discharging the battery - probably blown diodes - explains a lot!