[rxter]

My wonderful lead acid battery overflowed (I presume when charging) and dribbled all over the battery box. it ate a little hole into the pass side footwell where we found dried battery acid on the ECU and relays. No permanent damage but jeez if its not one thing...



Anyway, in cleaning up the mess I did not find an obvious spot for the missing battery drain tube.



You can see the tube, #14, which is speced as 250 mm long. There is a place where water drains to the rear of the front fender well, but a 10" tube won't reach that far down and I'd hate to vent that stuff onto other metal.



thanks



   

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[SILVY968]

Buy a longer tube and run it out of the fender opening, far away from metal parts.

My non OE battery came with an overflow port as well, I just got the right size plastic tubing and ran it out of the engine bay.

Brian

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[rxter]

After I dissolve and scrape off the rust, prime the pan and cover the hole into the pass compartment - arghhhh.. Thanks Brian that makes perfect sense. Time for a new battery anyway - this time I am going gel with an Optima. I hate battery acid...



By the way where did you route the tube?

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[Bob Kovacs]

FWIW, I bought my 1993 968 in 1999, when the car was just six years old, and had to replace the battery almost immediately. I found that the battery well was rusted through (after just 6 years!), so I scraped out the rust and came up with the idea of patching it with POR-15 paint and glass fiber cloth. I didn't any resin for the glass cloth, just the POR-15 paint. I'm here to say that this patch has held up perfectly and still looks pristine 14 years later. I just replaced the battery again and there is no hint of rust or any indication that the POR-15-soaked glass fiber will delaminate from the underlying surface. If anyone has to make that repair, that's what worked for me.



Bob Kovacs

www.bobkovacs.com

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[MB968]

Fortunately my battery area looks great so far. My Mazda came with a glass filled polymer battery tray that worked great. Does anyone know of any aftermarket battery trays that would work in our cars. Might be worth adding one just as a preventative measure.



Edit: And, never heard of a battery drain tube. Haven't seen one on my battery, but guess I need to look to see if there is a port there.

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[Carl968]

Hey guys - where is this drain tube routed?? I have a rubber grommet on my firewall under and behind the passenger side hood hinge. Is that where this routes or is there another spot. Can't seem to find any other holes but haven't removed the battery yet. Carl

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[rxter]

The drain tube is not meant to take overflow and route it away from the car. If you think about it a bit that would make no sense. If you have a battery that is "draining" then you have a problem. This tube is simply a vent. Lead acid batteries are typically vented so that the H2 gas does not build up and crack the case. Most are vented at the cap rather than on the side like the Bosche.



After thinking about this for a while I remembered that I have been putting lead-acid batteries in my cars for 40 years and have only occasionally had a problem with acid overflow - and I never had a "drain tube" before. So, upon further inspection I found that the source of the acid that ate a bit of my tray was a tiny crack on the bottom of the battery. After cleaning it up, glassing and painting the hole I took the cracked battery to Pep Boys and the manager gave me a new one. I put it in and forgot about it.

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[MB968]

Carl, I'm not sure of this, but ran into a guy locally with a 944 who had his battery area fill up with water, due to leaves plugging the cavity drain. I'm pretty sure there is a water drain in the battery area on our car. I don't recall if it is under the battery or not. If there is a gromet going through the firewall, that would not be for the battery drain, or it would drain into the cabin. If there is a hole for the battery hose, it would go out the bottom, or the side, down through the fender area. Whatever you do, don't plug the drain hole that is in the battery area with a drain tube from the battery, or you could have other issues.

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[Carl968]

MB - Exactly as you stated there is a sort of channel or groove under the battery on the fender side that drains the liquids from the battery box area. It does go behind the fender liner and out the bottom. After further investigation I did find it but thanks for your response. It is great the way solutions are resolved on this site.

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[MB968]

I've never seen a battery with a hose; what rxter said makes sense. The hose is just a vent. Since the gases generated can be explosive, maybe this is just this bat. mfg. way of getting the gasses away from the potential of a spark at the terminals.

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[flash]

i've seen it a few times. not often though. bosch does it on theirs. i had that vent on the one in the M3.



a lot of motorcycle batteries have it though.

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[tamathumper]

Regarding motorcycle and ATV batteries, I think the tube also helps prevent major leaking in the event the vehicle ends up shiny-side-down.

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[flash]

that doesn't make sense. it wouldn't drain up.



i think it's in the event of high rev overcharging. motorcycle charging systems used to be very different than cars.

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[bombfactory]

Yes, the 'battery drain tube' we're talking about has nothing to do with the battery, it drains water running off the windshield out of the battery compartment area. It's a VERY good idea to keep it clear and free of debris.



How do I know? Here's my sad sad story:



Sometime in the distant past, my car, under a previous owner, had that drain tube clog up and somehow rain water overflowed into the passenger area of the car. The water was cleaned up, the drain tube cleared out and everything was fine after it dried out.



Fast forward ten years later to about six months ago.



I take the 968 to pick up some Chinese take-out. On the way out, when I try to start the car it cranks but won't start. I try a second time - cranks but won't start. I try a third time - no crank, and then a huge cloud of white smoke starts pouring out from under the passenger side of the dash, and continues for about a minute. I seriously thought the car was going to catch fire and burn to the ground.



After much investigation and pulling of wires, my mechanic determined the water that made its way into the passenger area soaked the wiring of the passenger side airbag control module and the alarm module on its way through, and after a decade the creeping corrosion finally got bad enough to cause a meltdown.



Thinking back on it, I did have a warning sign: A few months before the meltdown the alarm started going off for no reason a few minutes after I'd lock the car. I just pulled the fuse and the relay and didn't think much of it.



Keep those battery area drain tubes clear boys and girls - or your car could look like this:



   

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[flash]

we are talking about 2 different tubes. there is actually a battery drain tube on some batteries.

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