Does this sound like my alternator going south?
 

My new to me V70 Classic 2.5D is going great @ 117k miles.

Well it is, until I get to 65-70mph, when the battery charging light comes on solid red. Most of the time this week it has been wafting around less than that speed and no warning light.

It starts first time, no dim or brighter headlights, or anything else strange.

It's booked in at my local garage next week, but on the face of it, does this sound like an alternator going down?

Not sure when the battery was changed, but it is a 75 mha.

Never seen this before - has anyone had it happen? Also, what would be a reasonable cost for a replacement alternator / aux belt for this engine?

Many thanks in advance, Mark.

It's 30 mins and £45-50 for a replacement on eBay. If you change the regulator only, £15. And it will be the regulator 9 times out of 10. They can take several thousand miles to finally die or stop working in an instant.

Don't know about the diesel. With my 1999 petrol, I found one from an S40 fits

Not sure why you're asking if you're fannying about with a pro to do the job, just do it.

Quick update - have had the battery / alternator checked at local garage and both were operating within spec.

What I have noticed is that the aux belt tensioner rattles especially when the AC compressor is engaged.

Would that be a plausible reason for the charging system to be throwing the battery light on at higher speeds? ie. the tensioner is not operating correctly?

Many thanks in advance.

Can't say for sure the tensioner is the cause of the problem but if it's rattling get it changed immediately[I'd change the belt too]as I believe if the belt lets go it can tangle with the timing belt with it trashing the engine.

Probably wise to check the aux belt tensioner and idler.

I found on my 1998 V70 Tdi (mechanically the same engine as the 2.5D) that the tensioner pulley bearing had got a bit stiff and notchy feeling and the idler pulley wasn't far behind it. They should spin freely.

The aux belt tensioner and idler both use bog-standard industrial bearings sandwiched between a pair of flanges held together by rivets to form the pulleys and if you have the time and inclination, these bearings can be replaced by drilling out the rivets, separating the flange plates and prising out the old bearings then reassembling with new bearings.

I replaced the rivets with machine screws and Nyloc nuts. The bearings should be stuck in the flanges with a suitable threadlocking adhesive otherwise they can fret and wear their way through the flanges. Unhelpfully the bearings used in the tensioner and idler are different.

It's probably worth a good look at the state of the harmonic damper which forms the crankshaft pulley too.

On the plus side, the cambelt is very well protected on these engines so an aux belt failure is far less likely to be the catastrophic event it can be on the later D5 engine.

Assuming there's enough tension on the belt to allow sufficient power to be transmitted to the alternator, power steering pump and the A/C pump for them to operate normally, I'd have thought it unlikely that a problem with the tensioner would cause the problems you describe.

Is the problem intermittent or does it happen every time you hit the 65-70 mph speed range?

It would be interesting to monitor the battery voltage to see what happens to it when the red light comes on since this would provide some clue as to whether the alternator was still delivering current.

Martin,

1998 V70 Tdi auto.

Thanks for your help Martin - great to hear about your experience with the engine.

What I am trying to avoid is just replacing parts willy nilly. The car always starts first turn and everything electrical appear to be working fine - AC, headlights, stereo etc.

The battery light is fairly consistently on over around 65, but not always.

Is there an easy way to monitor the voltage as you suggest at the end of your post? if there was some gizmo I could plug into the cigarette lighter that would be a boon.

Perhaps I should just carry a brand new spare battery in the boot;-)

Enjoy the rest of your weekend, and many thanks again.

Since your car is the 2.5D it will be one of the last Ph1 V70s so it's likely to be OBD compliant which the earlier ones, like mine, were not. So theres a good chance that one of the phone app based monitors may work. It's not something I've any experience with since they won't work with my car.

Failing that, a digital voltmeter connected across the accessory socket and monitored by a willing passenger should do the job.

Martin