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Conflicting information Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 16 Jul 2002 15:42:45
In Reply to: Is my battery or my alternator??, jules, Tue, 16 Jul 2002 12:40:09 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Mid-13 volt range is OK while driving around, assuming it's a warm day - alternator voltage output is temperature compensated, and is lower with high temps.
You say you see 10.5 volts - was this when you first start the car and before you've driven off, or is this after you've moved the car a few hundred feet? When the car is FIRST started, the EDU shows a 'startup' voltage, which is approximately how low the battery goes when cranking. This voltage will kick over to 'normal' volts if (1) you hit the INFO button a few times, or (2) you move the car a few feet.
A low startup voltage is a sign of a weak battery. "Low" varies from car to car, but low tens/high 9's is usually a poor sign.
BUT, if you're seeing anything less than 12.5 volts after the car has started moving, even if it's just idling at a light, then that's a sign of a weak alternator. Anything less than about 12.3 and you'll see the battery light on, or at least flickering. You didn't mention battery light issues.
If you always see 13.0 or more after the car has started, even just sitting at a light, then the alternator is probably fine. The problem is that starting a car takes a lot of juice out of the battery. Once the engine is started, the alternator has two jobs - first to supply ALL of the electrical needs of the car, and second, recharge what was lost from the battery. That takes some time. If you are really taking lots of very, very short trips, the battery won't get fully recharged. Car batteries are designed to run at full charge all the time; if they get partially discharged, chemical reactions inside the battery cause buildup on the plates, reducing the battery's capacity. And that buildup is pretty much irreversable.
If you really are only driving a mile, then letting the car sit all day, the battery will take a beating. Not only that, the engine is taking a beating - the oil NEVER gets hot enough to burn off the water it absorbs, so there is lots of moisture doing evil in your sump. A tank of gas will go forever, but that gas will absorb water and do evil in the tank and fuel system.
At least once a week, more is better, take the car for at least a 20-30 minute drive. Make sure it gets up to temp and stays there for 15 minutes or so. This will keep the battery charged and the engine otherwise happy.
My guess is that the battery is overstressed and on its way out. Get a fresh one, and keep it healthy by driving the car.
Good luck!
posted by 140.157.4...
, Tue, 16 Jul 2002 15:42:45 <-- Viewing This Message
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