What would pop the caps off the battery?

My '92 240 wagon has been running well and I've been driving it all day.
However, when I just went to move it into my parking spot from the street,
there was a bang.

Opening the hood, the caps were blown off the battery and while there is
some power - the locks and the dome light work - there is no response from
the starter to the ignition key. As well, only a few of the warning lamps
come on when the key is turned, instead of all of them. The fuses are
intact.

Guess I'm calling the garage first thing and then a towtruck, but would
anyone have an idea of what's happened?

thanks..
Patrick Keenan

 

Overcharging. If the voltage regulator fails and the charging system puts
too much power into the battery, it can boil the electrolyte and pop the
caps off. You need to fix the charging system and replace the battery.


Gary

 

Actually the electrolyte isn't boiling - you're breaking down the water
into Hydrogen and Water. One spark (sometimes can even come from inside
the failing battery) and you have anywhere from a minor mess to serious
damage, depending on how lucky you are. But I agree - check the
charging voltage and definitely get a new battery. If the battery fails
in a certain way, one cell can be shorted, the other 5 will be
overcharging even at the correct "normal" system voltage, so the
charging voltage may be OK.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Thanks to all for the hints. Towtruck's on its way, and I'm glad to know
that this electrical problem likely isn't terminal (so to speak).

Patrick Keenan

 

And it seems that the voltage regulator had failed and so over 16 volts was
present. New battery, rebuilt alternator, problem is solved.

Thanks again
Patrick Keenan

 

Maybe it's a Volvo thing ;-)

My old 145 did that twice, but each time the battery actually blew up. The
first time it was on a cold morning, the second time it was 122 degrees in
the shade and the car was parked in the sun. Both times I hit the starter
and heard a POP. The mist coming from under the hood told me what had
happened. The hydrogen that is produced in normal charging had built up and
something in the starting process set it off. A nice chemistry
demonstration, but not helpful in getting anywhere.

Mike