Charging Question
 

Hi Guys, I'm going to post this for your opionion. I've got a long road trip planned and I want it all to be perfect.

Here's the situation from yesterday:

95 degree heat out here. Parked, idling watching sunset with a/c on, headlights on. I noticed the dash lights flicker, looked over at the volt meter - it had dropped a volt or two. When I step on gas and increase RPM, all back to normal.

15 minutes later, drove 3 miles (all OK and bright) to Starbucks, waited in car for my lady, same thing: Voltmeter showed drop, step on gas, all back to normal.

Now I've seen this a thousand times with other cars, but never with our XK8.

Is it normal to have a voltage drop while idling in these cars? I would have bet the car would increase RPM to keep it even, it seems to monitor about everthing else, but maybe not.

One more thing I should note: I am sensitive to how these cars need 100% battery charge, so once in a while I put her on the charger. Especially if I see a symptom like door locks cycling, or recently no starter when you turn the key (happened 1 in 5 times. It is always OK the second time you turn the key).

Lately I'm surprised to find that when I hook it up, the charger displays 8 amps (sometimes higher) and within 20-30 minutes shows full charge.

I welcome your thoughts. I'm probably just getting nervous about he upcomming road trip. I'll never forget the ordeal a year ago when my crankshaft pulley went bad at 7pm on Memorial day, in the bowels of NYcity.

Thanks for looking.

John

First insure your battery charging
 

Put a voltmeter across the battery terminals. At idle your battery should be charging at 14.8 volts.

It's easy to stop at a parts store like Autozone and ask them to test the alternator output and load test the battery. I suspect your battery is failing but testing both is the way to go.

A car in good condition that's driven even once in a while should not do this, and should not need supplemental charging.

You might have toasted the battery some time ago by letting it go flat.

Your dash VM isn't telling you much. Put a DVM on it and see what the voltage is cold, hadn't run over night, idling with all lights/AC on, 2k rpm. That will give us a clue if it is a weak battery, slipping belt or a failing alternator.

How old is the battery? Or you might be seeing the A/C compressor cycling when at idle which might account for the needle movement. If it were mine, I'd have the alternator load tested as well as the battery to put your mind at ease. By load testing the alternator, you can read what the alternator can put out under load vs. what its rated at.

Thanks to all. I brough it to Autozone this morning. All was OK, battery, alternator. . . until they noticed - the voltage regulator is bad.

Looks like I'll be replacing my regulator, next stop = Graham's instructions.

Autozone quoted me $219 for a new alternator. Anyone have experience with their brands or overall pricing? Frankly I expected a higher price.

Edit: Guys, I posted this before even a rudimentary search on Google. Parts Geek and many others sell alternators for our cars at around $113. Wow, I shouldn't be surprised with AutoZone.


Thanks,

John

Autozone (or any auto parts store) sources their aftermarket stuff from multiple vendors. There's no guaranty that the one you get will be from a good one.

You're far better off getting your present unit rebuilt.

Wow! I have the same issue and will be replacing the alternator again. Yes I have the same symptoms and had it and the battery tested at AutoZone.

Gus, it comes down to how fast do you want it. The lower priced ones are nearly a week from shipping ground. It came down to pep boys and Autozone for me. Pep boys use "manny30" for 30% discount. I went with Autozone.

Can't wait to see how complicated this job becomes. Keep us posted on your progress. John

Well this is how I did it the last time but if I see a change in the process I will make that known. This was done over 7yrs ago.

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