The acid smell... today.
On the way home from a friend mechanic shop to take care of the yellow ignition wire, I smell the acid smell. I thought to myself, can't be battery. My battery has been so good to me all the time. Maybe the oil leak and burn at the exhaust? Can't be oil burn since I am driving and the oil/exhaust is behind me. The more I drive, the stronger the smell was. When I got home, I smell the engine bay and below it, can't smell the oil at all. Everything is normal. When I look at the battery, it look normal. I even get the flash light out to look around it carefully (it's not dark yet). The whole area is dry and very normal. When I got my nose very closed to the batery, 2" closed, I can feel slight acid smell but the battery look very normal and dry. Probably when I am driving, reving the car, the smell come out stronger?

I then got the voltage meter out and measure across the battery poles. At engine shut off, I got around 13+V. At idle, I the V is jumping between 15.50v to 16.30v.
I came out at night, started the engine, rev it to 2.5kRPM and measure the voltage. Now it is at 14.3v steady when idle.

Summary:
Strong acid smell when driving. Battery look dry and perfectly normal.
Engine shut off, V between battery poles is 13+V, less than 14V.
Engine idle, V is jumping between 15.5V to 16.3V.
3 hours later, idling at 14.3v
Is it just the battery is about to go bad or is it the alternator? Or just the voltage regulator?

In the past, I used to guess it's the battery anyway. If still problem, I go to the alternator. Now I don't want to just guess anymore since if I replace the battery and if it's the alternator problem, then the alternator will kill the new battery again. Then I have to replace both (alternator and battery again). Also because I got you guys, the expert here.

Anyone know what is the exact problem? Or know how to troubleshoot this?

Now I know 1 good reason to install an indash voltage meter.

Thanks in advance.

 

Bad voltage regulator. The 15-16 volts from the alternator is boiling the battery thus the acid smell. Voltage should be low-mid 14 volts. The battery voltage with the car off should be mid 12's for a good battery, low 12's high 11's for a bad battery. This is for a car that has been shut off for a few hours, if you turn the car off and immediately check the voltage you will get readings like 13 volts which is what they call surface charge.

 

rnln: I don't know the year of your car, but if it's an '82 or later the typical cure for your problem is to have the alternator rebuilt, and the job MUST include a new voltage regulator.
Pete

 

If your problem is the voltage regulator over-charging the battery then you can partially overcome the problem by driving with high beams on. Your symptoms certainly indicate battery over-charging but that could also be due to a dead bbattery cell. Now your alternator is trying to charge 5 two volt cells to 12 volts.

 

rnln,

My original 1985 alternator lasted 63K, then a "factory" rebuilt lasted 78K. Last time I pull this myself and had it rebuilt by my local electrical shop for just over $100. The brushes and slip rings were almost totally gone.

I was getting some flicker on my headlights when starting at night; Drive down road for 5 minutes and lights dim. Also I was getting corrosion on the positive battery terminal. I don't remember the voltage readings.

Pulling the alternator is an interesting exercise. I've done it twice on the 911 so let me know if you need help with directions. It's kinda tricky but remember 'patience'.

Final note. I bought the regulator and was going to replace it myself but decided the slip rings were shot. The shop said with worn slip rings they have had the brushes break if just new regulator is installed (brushes part of regulator).

 

I replaced the original alt (~60k, 22 years) and the battery concurrently last summer (about this time, actually). New factory alt was ~$330 from memory, battery was ~$100 or so). I was told one for a Golf (?) was the same, online for ~$240. I paid the core on mine, kept the oem, figured it'd be cheaper to have that redone professionally & keep it on the shelf for a spare for the next time around that way.

 

Thank you all for so much info. I will spend a little daily in the eve to take it apart and let see.

Peter Zim,
Rebuild alternator involve with VR, burshes, and bearing. Am I right?

Glennof,
If slip rings is worn, it will eventually break the bushes of the new VR. Do I get that right?

Again, thanks all.

Last time I bought the bushes (VR) for my BMW 325. It cost $13. This 911 VR cost $53 bucks. What the diff.

 

<b>Update...</b>

As what I first decribed, high voltage on battery poles, no doubt everyone will point right at the Voltage Regulator. Because I said the battery looks perfectly clean.

I plan to slowly taking off nuts and bolts one by one every day I get home after work but I get so lazy. Every time I got to the car, I hold my coffee cup and a garette, or start the engine and walk around the car touching it here and there until it's dark. Several times I let the engine run for proximately 1/2 hour or so, idling, reving slowly, etc... and the voltage got to max around 14.5v without any instrument turned on.

Today, I actually open up the hood and take the negative cable off the battery. Because I was too lazy to "work", I opened up the battery caps to see how it's in there. oups... I found something which it should be the first thing to check... there is no more water/acid in there.

This doesn't mean I solve the problem right? Because there still is a possibility that the battery ran out of water the same time the VR got damage. But there is a 50% chance that the battery is dried, and everything else is still good. Am I correct?

Now a new question I have. Long time ago in the old time, we use to go out there and get the distill water or acid to pour in the battery. Later on, I found that no place is selling distill water any more. There only place I know is still selling acid is the motobike shop but their price is not that nice.
Anyone know any solution on distill water/acid?

Thanks.

 

You should be able to find distilled water at the grocery store. Distilled is better as the minerals in undistilled contaminate the batt. You may have fried the battery by boiling it dry but put some more water in and try it. Do not put more acid in. I would not waste money on more batteries until you get the alternator fixed. Take it to a reputable alternator shop to get it checked out.

 

The smell you had, have, is the result of the battery fluid BOILING off. So yes, you can add water but it will simply boil away again. And keep in mind that the GAS you are smelling is not only detrimental for breathing but is also highly...

..........EXPLOSIVE!

Be very carefull lighting those cigarettes.

 

So definitely the VR drank the battery fluid. Not the battery dry the fluid itself? So checking the VR is a must huh.
Thank you much guys.

 

No, an internally shorted battery cell, a fairly OFTEN occurrance, will result in the fully operational and correctly performing VR trying to (over-)charge what has now become a 10 volt battery to 12+ volts.

Sometimes you can detect a battery failure due to the fact that only one cell dries out, or one cell remains filled while the others dry out.

SOMETIMES.

So your problem could be either, the battery or the VR.

 

Not so sure about that ... I don't think the VR should be putting out 16v regardless. I once disconnected the battery while running and still got about 14.5 at the wires. Mine is a 78 so is afe to do this short term. Perhaps RNLN could try that while he is reading the 16.0v ? if he disconnects the batery and it drops to 14 you may have something. if it stays at 16v it ain't the battery !

Besides if he had a shorted cell and was running two lesser cells, I doubt it would even start,.


any thoughts ?

 

Disconnecting the battery while the engine is running can, WILL, quickly destroy any onboard electronics, radio, etc. I know of instances wherein it blew every light bulb that was turned on at the time.

 

rnln, not sure where you are located, but you might want to check a nearby Firestone or Interstate battery dealer to see if they have the ED-18 battery analyzer made by Interstate. It will give you a quick check on your battery's health giving you CCA, volts, good/marginal/bad or bad cell reading, etc.

It takes about 5 minutes and I do this at my shop for free. It will also check the charging system and starter to some extent. Just another quick way to double check your findings.

David