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Old 11-03-2002, 10:30 AM
Posts: n/a
Battery Venting Cloud Of Hot Acid

1991 560sel; 126K
At the end of ~100 mile trip Friday, I pulled into my driveway and began to smell something like rotten eggs. My first thought was "catylic converter" but the smell was not at the rear of the car. It came from the front of the car. With the engine still running, I raised the hood and found the battery spewing out a cloud of hot acid steam from its vent. The battery was very hot to the touch. The acid cloud continued to spew for 5 to 7 minutes after I stopped he engine and disconnected the negative battery lead.

Saturday, I removed the battery and found that the heat had actually caused the battery case to bow or bulge out in several places. My first trouble shooting thoughts were:
Alternator could be overcharging (I had been driving at highway speed for approximately 2 hours but no fault light had appeared on the instrument panel).

Electrical short somewhere in the vehicle (All of my experiences with electrical shorts were that a fuse would blow but no fuses in the fuse box were blown).

Defective battery (Possible shorting of battery plates. The battery was 3 months old).

Not being very good at dealing with electrical problems, I did the simple thing (for me) first. I replaced the battery. I started the car and everything seemed normal. The first half of the test drive was approximately 15 miles at highway speed. I stopped and checked the battery by smelling and touching. No smell and no abnormal battery case heat, so I turned around and started back. This time, I turned on the automatic temperature control.

After about 5 miles, I finally recognized that no air was coming out of the vents. I began to push the buttons. No high speed fan, no low speed fan and no automatic control. The temperature control should have signaled for warm air. I changed the control to see if the AC would work, but again, no air in either the manual or automatic mode. I could, however, feel the compressor clutch engage and disengage. I left the control on automatic and continued driving the 10 miles home. I pulled into my driveway and raised he hood. There was no acid spewing from the battery vent but the battery was starting to get hot.

I evidently have something that is shorted. Very possibly something to do with the AC or heater blower. I obviously have many questions but they all boil down to what to do and where to begin. I would certainly appreciate knowledgeable input on this issue. THANKS
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Old 11-03-2002, 11:14 AM
jbaj007's Avatar
Registered User
Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
Start by checking alternator output. Sounds like it started out as a classic regulator/overvoltage.
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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Old 11-03-2002, 07:04 PM
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Battery Problem

I had a very similar problem that the forum and I worked out together. Mine was a Voltage regulator problem. A $14 dollar part and and battery and I'm good again. I provided a link below to the thread in this forum about the problem. Check there and It may help you. The posts near the end are where I found the problem and It's pretty easy to check with a small volt meter.


Spewing Battery !

Last edited by whunter; 03-15-2006 at 03:12 AM.
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