Jaguar Repair: Jaguar XJ6 S3 4.2 auto Charging Problems, belt tension, jaguar xj6

Question
QUESTION: Hi Howard,

I have a 1982 XJ6 S3 4.2 auto which has a charging problem that nobody seems to be able to solve for me.

I have replaced battery with new twice in last 3 months but problem remains. The alternator does not seem to be charging battery at all and I have to jump start it each time from other car.
When engine is running the voltage at the battery terminals is 14.1v at all engine speeds and with lights etc on or off. After a long run and switching off engine the voltage at battery is around 12.5v but then when I try to start it again (even immediately after a long run)there is barely enough charge to turn engine let alone start it.
I have checked that nothing is draining battery by removing earth lead and placing ammeter between earth terminal and earth. No current whatsoever leaking. Have checked belt tension and that's ok. Red ignition light goes off and remains off after starting, under all load conditions.
I am at my wits end, hope you can help!

ANSWER: Hi Paul,

You have a puzzle. The 14.1 v at the battery after starting is a 100% clear indicator that the charging system is operating correctly and due to the "No change" up or down the RPM range indicates the regulator is correct. 12.5 v with the engine still is an indication the battery is ok. The "IGN" red light out after starting is an indicator that the alternator has started to charge.

Your no start condition needs some testing. First do this, have some one hold the starter engaged for several seconds when it will not start and note any noise. (or is it spinning the engine but not starting?) Let me know what noise you hear under the hood and where it is coming from. (firewall or starter area?) As soon as the starter has been held engaged for several seconds feel the battery posts (both) to see if either is warm to the touch.

Next, put a voltmeter (on a low volt scale) on the battery post bolt (not the cable end) (negative test lead to negative post bolt) put the positive test lead on the head of the engine and have some one try to start the engine and no matter what happens (start or no start) read the volt meter and give me the voltage reading.

Rather then your ammeter test, use a standard 12v test light between the battery cable and the battery post (Everything turned off in the car and the doors closed) to see if it will light the test light and let me know.

Question! Is this battery a "Deep Charge" battery (Diesel or Marine battery)? Are you replacing these batteries with used batteries or new? Why didn't the parts store load test the first battery when it was a problem?

Howard

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QUESTION: Hi Howard,

Thanks for your rapid response last week, I've carried out the tests you suggested and reply as follows:

Starter turned engine half a turn then stopped, with key left in start position for several seconds battery posts remained cold. Voltage between -ve battery post and engine head went from +0.53v to zero when trying to start.

Test light placed between -ve terminal and earth lead did not light.

The first new battery I fitted was one I bought off the internet: 60AH, 605CCA, 100RC. The car became harder to start gradually over a couple of  weeks even though I had taken it for a few long (half hour or so) runs. I assumed that I had bought a dud battery but as I hadn't kept the receipt I could not return it to supplier. I bought the second new battery locally from a battery dealer This had same capacity as the first one but same thing has happened. Don't know if they are deep charge batteries (never heard of these!). Incidentally, how long should it take to fully charge a battery with the alternator from flat after jump start?

As soon as I connect jump leads from my other car the engine starts immediately. This weekend I will have access to a charger so I will give both batteries a full charge and then can start from a clean sheet as it were. I will then keep log of battery voltage before and after runs, length of runs etc and let you know.

Thanks again,

Paul

ANSWER: Hi Paul,

First the alternator can not bring up a dead battery except on a very long driving time because a good portion of the charging is going into the operation of the car and very little is recharging the battery.

A "Deep Charge battery" is a diesel or marine battery and is designed differently then a conventional battery. You have already made the preliminary test for a battery problem when you say it starts with a jumper battery. YOU NEED A DIESEL (DEEP CHARGE)BATTERY!!!

The voltage drop test of the ground cable (+0.53v) is ok. To be safe you should do a voltage drop test of the + side too by connecting the + test lead to the battery + post (not the cable end) and put the negative test lead on the positive post of the starter solenoid. (not easy to access) and hit the starter and you should see low voltage also. You can skip this test if you can't access the solenoid post.

To test the alternator out-put just, put your volt meter leads on the battery posts (not the cable ends) and read battery voltage (12.5+) Then have someone start the car and set the RPM at a fast idle (about 1500 RPM) and read the voltmeter. (13.8v to 14.5) is normal.

The series III Jag requires a Deep charge battery and unfortunately as soon as the battery starts showing it's age you will need to purchase a new one. The old one can be used in another brand of car for several more years.

Howard

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QUESTION: Hi Howard,

Thanks again for another rapid response!
Looks like I will have to bite the bullet and buy a third new battery then! I've found one on the internet and would value your advice on its suitability before I order. It's spec is as follows:

NUMAX CXV24MF Calcium Leisure Battery
12v 86AH
Marine Cranking Amps: 1000Amps
Deep Cycle & Starting
Sealed Lead Acid

It has lots of good feedback on their website and is apparently used quite often in V8 diesel-engined Land Rovers.
I will of course have to check that it will dimensionally fit (it is slightly (45mm) taller than existing, and not foul the underside of the bonnet.

Please could you advise if you think this would be suitable.

Best regards,

Paul

Answer
Paul, I don't know anything about that battery and I wouldn't buy a battery over the Net. The battery you need is at most any auto parts store and the one that is applied to the jag happens to be the same battery as used by one of the GM diesels. (and will fit your battery box and hold down. "Cold cranking amps" and "deep charge" are not the same thing, even though most deep charge batteries have a high cold cranking amp rating.

Find a local parts store that caters mainly to mechanics rather then the "grocery store" type auto parts stores. Tell them your make and model car and that you MUST have a "Deep Charge" battery and if they ask for the dimensions, call another store. That means they are just trying to fit a battery. If they say "Hmmm! that is a side post, deep charge battery and also fits some GM diesel applications" then get that battery.

Howard