Hi guys, picked up a MK4 golf 2.8 V6 4motion for a turbo project but have been having a problem with the battery.

The only modification I have done to the car is added a second inline fuel pump for higher power, I've got a positive running from the big 100A fusebox 12v in, ground to the chassis, all being switched through a 30A relay that is switched from the stock fuel pump wire. So the inline fuel pump only runs when the stock pump is running.

The car starts fine, no problem. Left it a couple of weeks in this cold weather, still starts fine. Moved it around the driveway to wash it, restarted fine after washing, while reversing into where I park it, ABS and ESP dash lights came on, then airbag light. Still running fine I parked it up, switched it off and tried to restart thinking water might have done something and a re-start might show if the lights stay on or not. Turned over very slowly then all power goes out, needles drop and flutter, typical flat battery stuff.

The thing is, is that I checked if the alternator was charging and I was getting a good 14.3-14.4 volts at idle.

One other thing to note, since the inline fuel pump is quite noisy, when I first start up the car the pump is kinda quiet, then after about 30 seconds the note to the pump changes for a faster note and the trip computer display backlight gets brighter. Pump noise will also sometimes fluctuate a bit, not stay at a steady tone like I think it should.

I gave the battery a good overnight trickle charge a couple of months ago and it seemed to start and restart well, took it for a 15 minute drive and had no cutting out or low voltage issues.

One last thing is that because its a 15 degree V6 but a single cylinder head, there is smaller than usual head gasket surface so VW added an electric coolant pump that would run after then engine has been shut off so that the block and the head cool at the same rate.

Am I right in thinking that the battery might just be crap, only being able to hold a small amount, with the start, restart and coolant pump running while washing the car, draining the battery enough that the alternator can't charge properly/running off the alternator. And when I parked up it had no juice left?

It has also done this exact same thing once before and I can't remember if I had washed it or not. Doesn't explain the changing pump note and trip computer backlight getting brighter

Ive had to replace the batteries on two other golfs before so maybe its just the battery. If it helps I can test with a good known new battery, just let me know what/how to test

Regards

Dave

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Am I right in thinking that the battery might just be crap, only being able to hold a small amount, with the start, restart and coolant pump running while washing the car, draining the battery enough that the alternator can't charge properly/running off the alternator. And when I parked up it had no juice left?

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Get the battery tested. I had one that seemed fine most of the time but the charge dropped to nothing turning the key, ok after a short charge..

Turned out to be an internal short that only came along when a big load of amps required.. Absolute pain to detect, took it along to the local tyre spot and when he stuck the tester on it nearly went bang! He prised the top off and one of the cells was a mess. Horrible smell, black and white wet crud. Yuk!

I've got to get a bulge in my tyre checked out tomorrow so will bring along the battery for a checkup

Yes by far the most likely cause is a dead (gassing) cell in the battery but it could also be back current leakage at the alternator or one of the cars systems not going into sleep mode.

As this is the time of year the cold weather reduces no load voltage of even a good fully charged battery by about 3/4 volt anyway put this together with the higher loads on the starter caused by cold engines and as a result many batteries die at this time of year.

The DIY test for a dead cell is with a reasonable charge in the battery to measure the battery voltage when cranking the engine from a coldish start, if it quickly drops from >12 volts to way less than 9 volts to usually about 6 volt then it points to dead cell.

We have an Audi A3 (53 reg) that had a fan that stayed on after switching off the engine and only stops when the battery is flat.
It was a common fault (£200 fix, ouch), not sure whether you vehicle has the same parts.

My 2003 R32 had a similar issue and it turned out to be the battery. These VR6 engines take a fair whack to get them started so battery would be my first suspect.

I'll try a good known battery on it and see if I get the fluctuating pump noise and display brightness. If it's all good then I'll get a new battery

Halfords brand ones okay? Lead acid or a calcium one for a tenner more that is supposed to have a much lower self discharge rate so works well for a stored car and comes with an extra year warranty of 4 vs 3?

Bosch s4 from eurocarparts. Order online and collect in store for an extra discount, far cheaper than anywhere else for a brand name.

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Originally posted by Slimy38
Bosch s4 from eurocarparts. Order online and collect in store for an extra discount, far cheaper than anywhere else for a brand name.

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Both only have up to an S5 battery, about 100 more CCA than other batteries and basically the same price at the halfords one, but with 5 years guarantee. Might have a winner, did a search but couldn't find any carparts4less discount codes though

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Originally posted by dave_424
Both only have up to an S5 battery, about 100 more CCA than other batteries and basically the same price at the halfords one, but with 5 years guarantee. Might have a winner, did a search but couldn't find any carparts4less discount codes though

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Thanks, there is another for £10 off when over £75, there is a £10 difference between the s4 (680CCA 74Ah 4 year) and the s5 (780CCA 77Ah 5 year) is it pointless to go with the s5?

It took some finding it, but here's the post from 3 days ago
Car Parts 4 Less voucher

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Originally posted by IanSouthLincs
Hi Guys, there's a generic voucher valid at the moment SAVEME75 gets you 7.5% off all items.

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To be honest, I focused more on the brand, I've never had issues with Bosch. The S4 was the one that was marked for my Toledo V5 (one cylinder down from your behemoth!), the S5 marked as an upgrade. The price difference was a bit more when I was after one.

Thanks Slimy, Gremlin and everyone else for all your help, I will try a known good battery on it tomorrow and if it cures it I'll pick up the S5 with discount coming in at £78.99. Great price, good brand and the top spec battery for less than the halfords cheapy

When buying batteries the 4 or 5 year warranty Bosch/Varta or Exide are safe bet.

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Originally posted by dave_424
Thanks Slimy, Gremlin and everyone else for all your help, I will try a known good battery on it tomorrow and if it cures it I'll pick up the S5 with discount coming in at £78.99. Great price, good brand and the top spec battery for less than the halfords cheapy

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Cheers for the heads up BritishTrident, I'm used to paying the halfords prices for batteries. So am I right in thinking that this battery is the same as the Bosch one but much cheaper?

http://www.tayna.co.uk/Varta-VW-1J0-915-105-AE-Battery-1J0915105AE-P9543.html

I once had to buy a replacement battery for my daughter's Golf GTi - checked out various places, and the cheapest by far was the local VW dealer! They sold premium grade at a stupid price, and 'general-purpose' grade at far less. I think that was a Varta.

Worth asking them anyway, if you haven't already...