How to properly jump-start a car

Before asking someone to "jump-start" your car, it's worth remembering a few important points.

Only a working car can be "jump-started." This is only permissible when the engine, battery, and wiring are all in order, and the battery is simply dead—for example, after a long period of parking, due to forgotten interior lights, or headlights left on.

If there's a smell of gasoline from under the hood, the battery has drained after long and futile attempts to start the engine, the wires are covered in dirt or damaged—"jump-starting" is strictly forbidden. This not only won't help but can also "kill" the donor car's battery.

If the headlights, stereo, and interior lighting work, but the engine is silent—the problem isn't the battery, and "jump-starting" is useless here.

Only a working car can be jump-started

Only cars with engines of similar displacement can be "jump-started." Different engine sizes require different starting currents, for which the battery is selected. Therefore, a battery from a small car is unlikely to revive a multi-liter engine—it will more likely just drain itself.

A diesel car cannot be "jump-started" from a gasoline one for the same reason: a diesel requires a much higher starting current than a gasoline car's battery can provide.

In severe frost (below -20°), "jump-starting" may simply not work.

How to properly "jump-start" a car

So, the car with a dead battery is working, and the donor car has a similar engine displacement and runs on the same fuel (or a gasoline car can be "jump-started" from a diesel one).

You'll need: jumper cables and protective gloves.

The connection points of the "crocodile clips" to the cable should not be crimped but reliably soldered. The wires and clamps are color-coded: red for "plus," black or colorless for "minus."

Step 1

Position the cars close together so that the cables reach. The cars should not touch each other.

Step 2

Turn off the donor car's engine and switch off all electrical equipment in both cars.

Step 3

Connect the "plus" of the charged battery to the "plus" of the discharged one with the red cable.

Step 4

Connect the "minus" of the charged battery with the black cable to any massive unpainted part of the body or engine of the second car.

This is done for several reasons. If the discharged battery is actually faulty (for example, short-circuited), the small resistance through which the current will flow will give the owners time to notice the problem and disconnect the cables.

The second reason is to keep the spark source away from the battery: with the high currents that occur in the first minutes of charging, the battery can emit detonating gas (a mixture of hydrogen and oxygen), and even the slightest spark can cause a fire.

First, the "plus" is connected, then the "minus"—also for safety, to minimize the risk of accidental short-circuiting.

The cables must not touch moving parts of the engine.

Step 5

Try to start the car with the dead battery.

If it doesn't work, it means the battery's discharge current is too high, and continuing attempts may drain both batteries. In that case, proceed to the next step.

Step 6

Start the donor car. Keep an eye on the battery and wait 10–15 minutes while it charges.

Step 7

Turn off the donor car's engine and only then engage the starter of the second car.

You cannot start the starter while the donor engine is running: this can damage the alternator (at best, blow fuses). The reason is that when the starter of the "jump-started" car is engaged, the voltage in the circuits drops sharply, and the donor's alternator tries to compensate for this drop.

Step 8

If the car starts—disconnect the cables in reverse order: first "minus," then "plus."

If it doesn't start, you can repeat Step 6 once more, but there's no point in doing more.

There are other ways to "jump-start"

There are many ways to "jump-start" a car, and they all differ both in the sequence of actions and in the actions themselves.

There are methods using a light bulb to determine the battery's discharge level (it serves as additional resistance), options for swapping batteries or switching contacts while the engine is running, and others.

But it's worth remembering: a modern fuel-injected car is packed with electronics, and the "jump-starting" methods used 30 years ago can now seriously harm the car.