Here’s the sitch: I have a very old car that I’m not interested in putting a lot of money into. It also has an old battery (either 7 or 9 years old) which I would replace if that’s all it was. But I don’t know. The battery has been dying, and while it invariably starts up immediately on being boosted, it dies overnight (or over the course of a day). Which is all consistent with an old battery. But here’s the odd part.
Yesterday morning I jumpstarted it, and after I turned on the car with the good battery, before the key had been inserted in the car being jumped, the engine cranked a couple of times (not enough to actually start it). And when the car was turned on, it made a couple of times that screeching noise that happens if you absentmindedly turn the ignition key while the car is already running.
So it looks like the car is trying to turn itself on without the key (the car does not have auto-start). In fact, I’m even wondering if perhaps the battery is still good, and what’s draining it is that this has been happening while no one is around but each time it drains the battery a bit. In any event, regardless of whether the battery is still good or not, it does suggest that there’s something else going on, and I don’t know what that might be or if it’s worth fixing. From looking around a bit, I’m seeing the suggestion that the starter solenoid is either mis-wired (which doesn’t seem possible here, since the starter system hasn’t been touched in years (possibly ever) or that it’s malfunctioning.
FWIW, the car is a 2000 Chevy Prizm (Corolla) with about 277K miles. Still drives fine, but the engine burns oil, the suspension is shot, and the body is rusty. So I’m not looking to put a lot into it, but for a couple of hundred I would repair it.
I’m thinking to swap out the battery with one from another car I have (same battery) but if it’s completely obvious that the self-starting can’t be caused by a bad battery then it sounds like a waste of time.
I know the respective sounds of a belt and a starter. Let’s not quibble about lingo. For purposes of this discussion, let’s assume it’s the starter and not a belt.
The chance that the car is engaging the starter by itself is extremely low. Not impossible, just very, very unlikely. There are multiple interlocks to prevent that. If it was occurring, you would probably notice that the car had moved by itself. So, move on to another theory.
All sources I’ve seen point to something involving the solenoid, either miswired (which seems unlikely in this case, since the wiring hasn’t been touched in forever) or faulty.
But what’s a bit different about this is that it seems like it might be connected to being jumpstarted. Because while the two cars are hooked up it does the intermittent starter screeching (or grinding, if preferred) thing, but it does not do it once the jumper cables are detached, even with the engine running.
A bad battery won’t cause the starter to engage. I personally had a car with a starter that had a bad connection in the starter (technically in the solenoid, which was part of the starter) that caused it to periodically engage on its own. I found that out the hard way when I was under the car trying to see what was going on with it and it started on its own. Wheeee! Fun. I don’t think I have ever scooted out from under a car so quickly.
You might need to replace the starter. Look for a loose wire or a frayed connection before yanking the starter out. It doesn’t take much current to engage the solenoid on most starters, so a frayed aging wire that accidentally makes a connection between the battery hot and the solenoid start connector could cause an uncommanded start.
If the car has a tilt steering wheel, try tilting it to a different angle. If the wires inside are frayed and touching that might move them apart enough that they no longer touch. Or it might make it worse.
I suspect that your battery has lost quite a bit of its capacity from being drained so much. You will probably need a new battery as well.
If you have a volt meter, test the battery voltage after the car has sat for several hours. If it reads around 12.5 volts, then it might be OK and it’s not likely getting a negative draw while the car is just parked. When running, the volt meter should read 14 or more volts so that will show your charging system may be fine too.
Still, a battery that old may have a short inside that only acts up from time to time.
I just went outside and tested that. In its dead state, it reads about 10.4 (vs about 12.4 for the good battery in the other car). I jumped it again, and as it runs now it’s about 14.6 (same as the other car when running).
Based on your post it looks like the battery was dead but charges up fine when it runs. So the question is if it’s failing to hold the charge or if it’s charging up fine but then drawing down again. I suppose I should let it charge up for about 15 minutes and then turn it off and test again. If it’s right back to 10.4, then the battery is gone (though there would presumably also be a starter problem), but if it goes to 12.4 or so then it would be just the starter. Is this correct?
Well after about 15 minutes of charging, I turned off the engine and measured about 13.0. After about a half hour with the engine off I tried again and it’s about 12.55. Does that say anything at all?
[In any event, if in fact there’s undoubtedly something wrong with the starter anyway, then I don’t know if it’s worth switching batteries, as above. But I’m trying to get as clear of a picture as possible.]
Anytime I’ve had questions about a car or marine battery’s health, I take it to the local independent auto-parts place and they test it under load. They don’t charge for doing this, and 75% of the time the battery is shot and I need to buy a replacement.
This raises an important point: measuring the voltage without load is practically useless. If the battery is totally dead or nearly so, it will of course tell you that, but it’s also possible for a lead-acid battery to register a normal no-load voltage yet fail catastrophically under load. I had a UPS that was once in that condition. It uses two 12V batteries in series and each of them tested at around the expected 12V. But it couldn’t do its job – it failed instantly when the power went out. When I took it in to a UPS shop they tested the batteries under load and one of them was totally shot. I replaced both and it works perfectly fine again.
ETA: This is an APC SmartUPS rated at 1500 VA. It’s a fine piece of equipment, but I thought it rather odd that the “replace battery” monitor failed to detect this condition. The self-test function undoubtedly would have caught it, but the battery failure was quite sudden and the self-test only happens (I’m just guessing) roughly every couple of weeks.
When you jump it do you connect the negative to the negative terminal or to a grounded portion of the engine block or frame?
The negative terminal on the battery is normally grounded to the starter or very near the starter. I wonder if you have a bleed that is sending a small amount of power through the solenoid wire.
I do it to negative. (I’m aware that the official best way to do it is to find an unpainted metal surface, but my recollection is that you’re also not supposed to use something that might be connected to something-or-other and between this and that I just go with the old tried-and-true negative-to-negative.)
OK, so yesterday I swapped out the batteries. The replacement battery did not lose charge overnight, so I assumed that while it may have a starter issue, that’s not draining the battery. So I left it in that car this morning (bought a new battery at Costco for the newer car), and my daughter made it to and from work with no problems, so hopefully all is well.
