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Who Taught You to Drive?

Four reasons why the car won’t start

If your car is exposed to deep water, it might make your gasoline useless and cause a stall. With watered-down fuel, your car will crank, but it won’t start, as if you had no gas.

George Rizer for The Boston Globe/File 2012

If your car is exposed to deep water, it might make your gasoline useless and cause a stall. With watered-down fuel, your car will crank, but it won’t start, as if you had no gas.

Ask a mechanic why a car might not start, and you’re apt to get a scolding.

“When you say ‘won’t start,’ what do you mean?” asked Larry Rubenstein, owner of Route 1 Auto Service in Peabody. “There’s a crank [the engine revolves, making a whirling sound] with no start, and there’s no crank at all. Two different things.”

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Sitting behind the wheel of a car that won’t start (or crank) is never a good thing, particularly during winter. But how to know whether the problem is an easy fix, or whether to call a tow truck? Today we ask some master mechanics what the problem might be — as well as what it might cost to get your vehicle rolling again.

Here’s Part 1 of our stuck-car checklist, leading off with the most likely reason you’ll be late for work.

Dead battery

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According to David Protano, who chairs the automotive department at Boston’s Benjamin Franklin Institute of Technology, a dead battery is what strands drivers “probably 30 or 40 percent of the time.”

How do you know your battery is dead? Darkness, that’s how. With a dead battery your headlights won’t go on, your dashboard lights won’t go on, even your interior cabin light might not work.

With a dead battery, your engine will not crank, either.

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If you know you left your lights on overnight and your battery is fairly new, a jump start should get you going. It’s tempting, at that point, to forget and move on. What you really should do is head to a service station to have your battery properly recharged.

“A lot of people don’t realize that every time a battery goes dead and you don’t recharge it, you lose a small percentage of its life,” said Rubenstein, who contributes automotive advice to “The Jordan Rich Show” on WBZ radio 1030.

If your battery is dead for no apparent reason, the culprit might just be the weather. A typical battery is designed to operate optimally at 60 degrees, Rubenstein said. For every 10-degree fluctuation from that mark, expect a 10 percent decrease in the battery’s cranking power.

“Let’s say it’s 30 degrees. You’re only going to have 70 percent of your battery for cranking,” he said.

If your battery is older and has endured a few nights with the lights left on, it will provide even less cranking power when the temperature falls.

“At 30 degrees you might have just enough power to crank the engine over. At 20 degrees or 10 degrees, you don’t have enough,” Rubenstein said.

An older battery will suffer in very hot weather, too, Protano said.

‘If you know you left your lights on overnight, and your battery is fairly new, a jump start should get you going. It’s tempting, atthat point, to forget and move on. What you really shoulddo is head toa service stationto have your battery properly recharged.’

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“Believe it or not, extreme hot and humid temperatures will terminate a battery if it’s weak,” he said. “The temperature, plus heat from the engine compartment . . . it just overheats the battery.”

How do you know when your battery is on its last breath? Unfortunately, there are few clues. It used to be that a dying battery would crank an engine noticeably slower than a fresh battery, Rubenstein said. “But now they just up and die.”

If your vehicle has a dashboard voltage meter, a drop below 13 volts should trigger a warning light. But such meters are increasingly rare in new cars.

“You should just know the age of the battery, and know, ‘I’m on borrowed time at this point, so I’d better replace it,’” Protano said, adding that factory-installed batteries often die out by year three. “Your service station will be able to estimate battery life left to within 10 percent. Just go in and say winter’s coming, I’d like my battery tested.

The cost of replacing a battery: anywhere from $75 to $300.

Frozen battery

Old batteries are also candidates to freeze in the winter, especially when you’ve accidentally left car lights on.

“When a battery discharges, the lead plates in the battery absorb the acids, so what’s left in the cells is just water,” Protano said. “Under 32 [degrees], and that water will freeze.”

Because water expands when it turns to ice, the sides of a frozen battery may swell outward, in which case you know what the problem is. But frozen batteries don’t always show such outward signs.

“With batteries that are serviceable, you can pop the caps off and look inside. But most of the batteries these days are non-serviceable batteries,” Protano said. That is to say, they’re sealed tight.

If you suspect your battery is frozen, either have your vehicle towed to a repair shop, replace the battery on the spot, or bring the frozen battery inside a garage to let it thaw out. “It might be OK, depending on the circumstances,” Protano said.

Never try to jump start or charge a frozen battery, he said. Why? “It could blow up.”

Shot fuel pump

“For an engine to run, you need a spark and fuel,” Protano said. “If you’re missing either one of those, you’re not going anywhere.”

Your vehicle’s fuel pump is what pushes gas from your tank to your engine. When your fuel pump dies, you’ll be able to crank your engine, but it won’t start. At that point, your lone option is to call for a tow truck.

Protano said that dead fuel pumps are to blame up to 20 percent of the time when a car won’t run. They typically last between 80,000 and 100,000 miles, though you have to be careful.

Most fuel pumps are located in the center of the gas tank, with the gasoline acting as a natural coolant for the pump’s motor. If you consistently run your vehicle on very little gas, the fuel pump will run hotter than it should, which will decrease its lifespan.

A fuel pump will also be pushed to its limit when there’s a blockage in the fuel line, said Carl Andrews, who also instructs at the Benjamin Franklin Institute of Technology.

“A lot of people forget that their fuel filter is supposed to be changed every 30,000 to 50,000 miles. Some people don’t change it until it’s at 100,000 miles,” Andrews said. “What happens is, the filter fills up, and the fuel pump will work overtime trying to push that fuel through the filter.”

It’s tough to know when a fuel pump is near the end, but Andrews said that poor running performance could be an indicator.“You’re not going to have that get up and go,” he said. “You put in a new fuel pump, and it’s like getting a tune-up.”

The cost of replacing a fuel pump: $200 to $800, depending on your vehicle’s make and model.

Water in your tank

Oil and water don’t mix. Well, the same can be said about fuel and water.

An ounce or so of water will render a gallon of gasoline completely useless, Protano and Andrews said. With watered-down fuel, your car will crank, but it won’t start, as if you had no gas in the vehicle at all.

Fortunately, water contamination is fairly rare. But it can happen, once again, when drivers fail to keep their gas tanks full.

“If people don’t fill the tank up, you have more of a chance of condensation, like the condensation inside a window on a rainy day,” Andrews says.

Protano said the only way to be sure you have watered-down fuel is to test a sample. If the results are positive, you’ll have to have your car towed to a service station, where they will either pump out the fuel with a neat tool called a “gas caddie,” or simply empty your gas tank if it’s equipped with a drain plug.

Next time, we’ll cover more reasons why your car might not start.

Peter DeMarco can be reached at peter.demarco@globe.com. His Facebook page is
“Who Taught You to Drive?” and on Twitter @whotaught
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