Does leaving your car on ACC drain the battery?

Question: I accidentally left my key in the "accessory" position over the weekend. On Monday morning, I had a dead battery. I was surprised, because the car is new. Nothing in the

Does leaving your car on ACC drain the battery?

Question: I accidentally left my key in the "accessory" position over the weekend. On Monday morning, I had a dead battery. I was surprised, because the car is new. Nothing in the car was turned on. Where did all my little electrons go?


Ray: Good question. Turning the key to the "accessory" position doesn't actually draw any electricity from the battery. It simply allows you to draw a limited amount of electricity to run certain accessories, like the radio, the power windows and the interior lights.

Tom: So something had to be on, despite your protestations. And because you've already admitted to being spacey enough to leave the keys in the ignition all weekend, we have to assume you're spacey enough to leave other stuff on -- like the dome light, for instance.Advertisement

Ray: If you're absolutely certain that nothing was switched on over the weekend, then the answer might lie in the ventilation system. In most newer cars, the blower fan cannot actually be turned off. Even when you move the switch to the "off" position, the fan continues to turn at a very low speed whenever the key is in the "accessory" or "run" position. And that would certainly be enough to kill the battery in 48 hours.

Tom: So that's probably where your electrons went, JR. They were keeping the air moving inside your car all weekend. What do they know? They figured you were spending a nice, relaxing weekend in there.


Q: I have a 1984 Chevy Caprice Classic. The engine is leaking all over the place. I need to buy a good rebuilt one. Please don't suggest that I buy a new car instead, because I can't afford one. I have found a site online that sells rebuilt engines and gives a 7-year, 70,000-mile warranty on them. My mechanic doesn't want to install this engine. He wants to get one from his usual source. He says it will cost me between $2,000 and $3,000 (that includes installation). The rebuilt one online (without installation) is $889.00. What should I do?


Ray: Well, I can tell you from the point of view of a garage owner that I wouldn't install that engine for you, either.

Tom: One reason is because I would have to forego my profit on the engine. And the other reason is that I wouldn't be comfortable guaranteeing the work for you.

Ray: Let's take your local pizzeria as an example. You go in, and he'll sell you a pie for $7. What if you came in with your own tomatoes, herbs, flour, water and cheese, and asked him if he'd use your ingredients and charge you only for the labor and the use of his cookware and oven? He'd tell you to flake off, wouldn't he?Advertisement

Tom: And the reason is twofold. One, he makes money by marking up the cost of his ingredients. Well, garages do the same thing. If a garage bought a rebuilt engine for $889, it'd sell it to you for $1,500. And that's legit. All businesses do that; they buy stuff at wholesale and sell it at retail.

Ray: The second reason he wouldn't use your ingredients is because he can't guarantee his pizza. Let's say you taste it and then spit it out and say, "This is awful! You've made a terrible, tasteless pizza." And he says, "It wasn't my cooking; it was those lousy ingredients you pulled out of the dumpster on the way in here." You guys yell at each other and disagree, he throws you out and you're stuck with a lousy pizza.

Tom: Well, the same is true with your engine by e-mail. If there's a problem, there might be no way for the mechanic to know if it was his fault or the fault of the rebuilder. So he might legitimately say, "Hey, not my problem." And then what do you do?

Ray: It's worth the extra money to have a mechanic you trust supply the engine and guarantee the work. But if you can't afford that, you can probably find a mechanic who is willing to install the online engine for you and just charge you for the labor (check the Mechan-X-Files at the Car Talk section of for recommended mechanics). So here's my advice: Ask your mechanic (and a Chevy dealer for comparison) for an actual price to install his own rebuilt motor. And ask him how long a guarantee he offers on parts and labor.

Tom: And then add up the real costs of the online engine. Find out how much the labor will be and what additional seals, gaskets and other parts you will need to pay for. Then you can see what you'd really be saving (my guess is $500 to $700), and you can decide if you want to take the risk.

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