DKWalser

I've another situation on which I could use the group's advice:

I've been using my '90 S4 as my daily driver since February. When I start out driving in the morning, the voltmeter indicates just over 13 volts. When I turn on the A/C and the fog lights (which I use as daytime driving lights), the voltmeter indicates just under 13 volts at idle. When I'm underway, the voltmeter returns to just over 13 volts. By the time the car warms up fully (the temperature gauge at the upper end of "normal"), the voltmeter indicates just over 12 volts at freeway speeds. At idle, it indicates less than 12 volts.

This has only been happening over the last few months as things have gotten warmer here in Phoenix. It didn't happen during the cooler months of February, March, and April. In May, every few days the radio started demanding that I enter it's code. Eventually, the car wouldn't start one morning because the battery was dead. (The battery was installed last August.) After charging, the car was back to "normal". The next day, when I returned home from my 20 mile to/from commute, my battery charger indicated the battery needed charging. (By the next morning, the battery was fully charged.)

I'm confident I could limp along like this just fine. Recharge the batter every other week and keep going until the weather cools down (ruining the battery in the process). However, I don't believe that this is normal and would like to fix it if I can. Ideas?

The only thing I've done so far is to replace the battery ground strap. It needed it. No noticeable change in the symptoms.

Kiln_Red

Sounds like normal operation of the voltmeter gauge to me. I wouldn't worry about the dash gauge. Apply a voltmeter to the battery if you want a more accurate measurement and peace of mind.

DKWalser

I understand that the dash's voltmeter isn't always accurate. I mentioned its various readings only as an indication of what's going on. In the cooler months of February - April, alternator output was sufficient to meet the needs of the car, run the radio and other accessories, and keep the battery fully charged. Since the weather has grown hot, the alternator output is no longer sufficient to meet the needs of the car, run accessories, and keep the battery fully charged. I know this because a) the voltmeter shows lower output, and b), the battery does not stay fully charged.

SMTCapeCod

I don't know that they are symptoms per se.

Sounds to me like the cooling fans are coming on and presenting a significant amp draw- significant but I don't think it is out of line with 'normal'.

There are stronger alternator options- bosch and otherwise (GM fit). Or, you could check the availability of the voltage regulator within the alternator and try just changing that- you'll probably need confirmation of the specific alternator to do that though. Marinelli, bosch, etc., unless that was standardized by '90.


Is the battery fairly new? Could be that its capacity for recharging is diminished a bit from the plates deteriorating over time, and that is the root-cause of the cold weather lassitude.

dragnayongj

Sounds like normal operation of the voltmeter gauge to me.

Dictys

I had the same symptoms on my car whilst in Dubai, worked fine in cooler months and struggled in the hotter months. The cure was two fold, having the alternator refurbished at a local shop and I also rebuilt the front engine harness as mine had perished due to the heat.

docmirror

This sounds fairly normal to me as well. A voltage test is a poor indicator of lowered alternator output. The alternator regulator will provide higher voltage to a system which has just undergone a heavy load like starting. The voltage will show high for a few minutes while the battery is topped up. Once that is done, the voltage will go down to a more nominal value and remain there.

If the car is running right, and there is no loss of starting torque from the battery, it's fine. The only way to properly test an alternator for load is with a load cell on a bench. You could warm up your car, remove the alternator, put it on a load cell and test it but my guess is it'll be pretty close to spec output.

A simpler but almost as effect test can be done on the alt while in the car. Follow instructions below. You will need a simple digital voltmeter.
1) Start and warm car to normal operating temp.
2) Turn off all accessories, have the minimum electrical load on the system as possible, only items needed to keep the car running.
3) Open the hood, turn off all the interior courtesy lights and close the doors.
4) Take a reference measurement while car is idling at the jump post on the right front inside fender. Make an accurate reading and write it down, it should remain pretty steady. Leave your voltmeter leads connected to the ground and jump post. example - ref measurement: 13.27V.
5) Get in the car, turn on all the courtesy light again, turn on the AC to high, lights, rear defogger, wipers, flashers, radio, and load the elec system as high as possible.
6) Check your voltage on the meter. It will be lower than the ref voltage above.
7) Rev the engine slowly and watch the meter. At some point around 2500 or so, the new meter reading will come close to your reference above. It may not reach 13.27 because of losses in the circuits due to heat and age, but the voltage will rise. If the voltage doesn't rise much when you rev the car, investigate the alternator and battery. If it rises very slowly as you rev the car investigate your alternator. If it rises quickly and reaches the ref voltage, investigate your battery.

Alan

Guys - the battery fully depleting every few weeks with extended daily driving is NOT normal - or didn't you read that part...?

BTW in Phoenix in the summer the cooling fans & blower are always on - 100% from start to shutdown - so there is always a high current draw

I'd check the alternator belt tension, but I think it will be OK (needs to be really really tight). I think you need a full alternator checkout - at least a new regulator and possibly new diodes. Take it to a real alternator shop that can truly test its operation under load, (there are still a few in Phoenix). Investigate if you can fit a slightly smaller alternator pulley while its there. I'd not be surprised to hear that 1 phase is not generating due to a diode failure.

My stock alternator did not perform well at hot idle in the high Phoenix summer heat (this is unfortunately normal) - however at speed it generated quite OK... So this is not in any way right.

Now you should have the battery tested also - you likely need a new one by now - deep discharge cycles kill lead acid starting batteries rather quickly. While the battery could be the whole culprit in some cooler places - I think this is rather unlikely in Phoenix, it would have self destructed by now to the point of no recharge/start.

Alan

DKWalser

Thanks, Alan. I appreciate the input. I'm afraid that I may have killed the battery and will get it tested.

I also appreciate everyone else who responded -- even though most didn't understand the issue. When so many people misunderstand what was written, it's only fair to blame the writer and not the readers.

Kiln_Red

I'll admit that I overlooked that portion of the original post. Or at least I don't remember reading it. Anyway, what is the current draw after the vehicle is stopped? A parasitic draw could be your issue. It may just be more obvious to you in the warmer weather because, as Alan noted, your car is using more juice.

Alan

I think you do need a new battery - but also I think it's unlikely that was the original causal probem.

Always good to check for a parasitic leakage issue - but here even just after driving 20 miles the battery was depleted - this suggests a weak battery and/or minimal charging from the alternator - likely both.

David to me your question was rather better stated than most...

Alan

DKWalser

It might be a parasitic leak, but I doubt it. I did a lot of traveling for business at the end of April and the beginning of May. After sitting for a little over two weeks, the car started right up. So, if there was a leak at that time, it was a small one.

When I picked the car up in California last October, I drove it straight home. During that drive, I noted that the headlights dimmed slightly when I turned the A/C on (which would cause the electric radiator fans to come on). So, I've long suspected that the alternator was not putting out enough juice. Things were fine if just the A/C or lights were on, but not both. Knowing that the summer heat can make these problems worse (and easier to diagnose), I've waited to see how the car responded to the heat. Now I know.

I'm having the alternator and battery tested. Armed with the results from that test, I'll have a better idea which direction to go. I'll be very surprised if the alternator does not need to be repaired or replaced. If the battery needs to be replaced, we'll see if Interstate Batteries will honor the prior owner's warranty. I've the receipt. If not, a new battery's not too expensive. Once this issue is fixed, I'll move on to upgrading my headlights to H4s with higher wattage bulbs and other things that demand more power. I've been holding off on any changes that might require more juice until addressing the alternator question.

Thanks, again. It helps to have this group to bounce ideas off of. It's a good reality check.

Hold On

Mine operates the same in the Arizona summer. If that 20 miles commute is stop and go in valley traffic, I can totally see the alternator not keeping up with the ac/ blower/ cooling fans/stereo/ and any other electrics that may be running at the time. The draw is tremendous at idle speed. Its a time/speed/output/draw equation. Dont you just love the valley in the summer !!. Do your checking of all components but do not be surprised if everything checks out OK. You may have to upgrade the alt. to meet the elec. needs of that environment.

DKWalser

I just received an email from the shop testing the alternator and battery. The battery is okay. The alternator, not so much. At idle, the draw exceeds the alternator's output by 20 amps (with A/C and the lights on). Things don't improve much at 3,000 rpm. With everything "off", there is a draw of 50 mA. Not much of a leak.

Note: I've not learned what's wrong with the alternator. The shop is recommending replacing it with a Bosch unit for $320, installed. (I don't know if that's for a new or rebuilt unit.)

Alan

For that money I'd expect it's a new one, take the battery back to the source and have them test it on a carbon pile load tester - I'd expect while 'good enough' - it is probably far from actually good... so collateral damage...

David if they aren't returning the used alt as a core - I'd be very interested in it for some experimentation...

Make sure they do put the shroud & hose back on! Did you take this to Dan at Exotic? if so he will take care of it all.

Alan