Good evening

Sitting in traffic this morning, lights on, heater on (its cold!) for probably 30 mins or so crawling along. Got part way to where I was going and stopped off to collect something. Got back in the car, battery almost dead, just about turned engine over but not enough to start the car. By an amazing stroke of luck I had another battery in the boot that I was returning under warranty as it would not charge fully and only a month old. Swapped them over and it had enough juice to start the car but straight away (and for the first time) I noticed the batteryometer or whatever the proper name is read very low. Usually was quite a bit over the 13v mark.

I was within a km of my final destination so I quickly headed back there but now with eyes on this gauge - noticed that with revs the needle was at around 13v - still a bit lower than normal - but as soon as I braked into traffic it dropped right down again to what I think is battery voltage about 12v. When I got to where I needed to a took a battery off another car - same thing - with revs it goes to 13v and at idle right down and eventually drains the battery whilst at idle.

I am assuming this needs an alternator but before I hit "buy" on my suppliers website I thought I would hit this forum for any other alternative (pardon the pun) views on it being anything else obvious that the more experienced folk may gravitate to instead.

Car is a 1995 X300 3.2 XJ6 with 135,000 miles on it, used almost daily.

TIA
Sam.

 

In your quest for electrical natonization and the battery's tummy full..................

 

Erm, okay! So you think its the alternator then - being serious, original battery was in the car when I bought it about 3-4 years ago and never let me down. Now flat. Used a slightly dodgy new one to get it going - same symptoms. Then a "known good one" and same. So definitely not battery ....

 

They fixed the house internet so we may begin

The only true way to measure the alternator is at the large B + battery cable post on top of the alternator as you dig down

You should see 13.5 to14.5 with the engine running and steady through throttle changes.

You can read it on it's path rearward to the battery on the right front wheel well arch near the rear firewall

But in between the fender terminal post and the alternator is a tie point at the starter solenoid that someone got a good picture of as his was loose causing charging issues

 

Thank you so much for the detailed advice and sorry I haven't replied until now. I parked the car up and have been driving around a Ford Mondeo for the last few weeks (sometimes I pretend its an X Type ....). I did do the tests you detailed at the time I parked it up and it was pretty conclusively the alternator. I bought a cheapy new one and today swapped it. Fairly easy job - for those who need to do this, here is what I did:

Firstly I should note that the car was left at my work car park and not in my garage so I used just tools I had in the boot. Basically a socket-set (1/2 & 1/25 drive JBM thing - I think they are pretty good cheapo sets). And a set of open ended cheapo spanners. I had no jack or stands with me and so I had to do the whole job from above (well almost).

Loosened off the adjustment nut on the threaded bar adjuster. 15mm deep socket. Loosened the bolt holding the adjuster to the engine - 13mm. Removed bar from top of alternator - 10mm. Move adjuster out of the way. Loosened lower bolt - 17mm. This frees it up so you can slide belt off. This is in-board of the other belt so just hangs off crank pulley. Then the first tricky bit - the long bolt at the bottom isn't threaded into anything - it has a nut on the end. To get this off with the car sitting on the ground have a helpful assistant hold it with a 17mm spanner - required a bit of fiddling around to blindly get the spanner onto the nut. Then undo the bolt fully - be prepared if you are working like this to scratch your hands up trying to reach down and undo it. Then the second tricky bit was prying the alternator off the mount with no pry-bar - just brute force and some leverage with a big spanner. Once off, turn sideways, remove plug, main cable - 13mm and control wire - 8mm. You can then turn it so its facing up and pull it out from above. New one in same way but make sure you knock in the retractable sleeve or it will be hard to get in. First reconnect all the cables. Then slot into position. Long bolt back in. Adjuster bar back on. I adjusted it at this point and did the lower nut afterwards. Fire it up and watch in awe as you have just under 14v on the gauge.

If you can lift the car the lower nut and bolt would be a one-man job. Also completely removing the adjustment bar from the engine would make things a bit easier space-wise.

 

Caution on removing the adjustment rod at the engine block if the belt is stil on it could pull and deform the threads on the engine block

this would be the point of deciding to cut off the belt and not have a harder time on reassembly.

 

Of no relevance now the alternator has been replaced, but did you notice whether the drive belt could have been slipping on the old alternator?

 

Hi there - yes I checked this. I had problems before with slipping belt especially on wet mornings. It would squeal and the volts would drop and after a few minutes grip fine with volts at circa 14v. When the alternator failed the first thing I did was check the pulley on it was spinning which it was but about 7v on gauge so this wasn't the problem. However this is a good point and a basic first check others should do if they face a similar situation

By the way I have kept the original Jaguar OEM alternator - I wonder if it is worth having it refurbished? The one I replaced it with was a STARK-AUTOMOTIVE which was around 120 euro delivered - Jaguar original one was closer to 500 euro without delivery.

 

The alternator you pulled off can be spin tested at the local auto parts store and the test results will let you target the items of concern.

The voltage regulator inside is a IN435 and the brushes and, diode pack can be obtained from the same vendor

I had bad luck with E - bay vendors giving a wrong VR that failed worst then the one I fried

But was able to catch this as a spin up test at the auto parts store before installation.

I had once on M"Lady Penelope the front alternator bearing fail and took to a alternator shop and had them replace the bearing

there was a terminal screw fusing on mine the VR lug to the brush lug so check before ordering fresh parts if you need both regardless of brush condition

I had half brush wear life left at 110 K miles

# IN435 Voltage Regulator for Denso Alternators, 12 Volt,On: Asuna (1993-1993) , Geo (1990-1993) , Isuzu (1990-1993) , Jaguar (1993-1997) , Jaguar - Europe (1994-1997) (alternatorparts.com)

The off brand rebuilt and new built alternators do not have a good track record lately from experience and reading