What is a solenoid?

Your vehicle’s starter motor has the important job of starting the engine. But something also has to start the starter. And that something is the solenoid. In most automotive applications today, the solenoid is attached to the starter, with the two of them getting removed as a unit when necessary.

How a solenoid works

When running properly, and as long as it has a supply of fuel, the internal combustion engine continues to run by itself in an ongoing process from the inertia of the engine’s moving parts. But starting the engine is a separate process to get that inertia moving in the first place. This is the job of the starting system, whose main components include the:

  • Battery
  • Starter motor
  • Solenoid
  • Starter switch

Starting an engine: The first action

The process involves not one, but two separate electric currents – a stronger one and a weaker one. When activated, usually by turning a key in the ignition switch, the weaker current passes through the switch and to the solenoid. At that point, the current forces two large contacts to come together in the solenoid, which allows the stronger electric current to pass through the solenoid’s contacts. These contacts carry a current that requires heavy wiring cables directly from the battery. This current is heavy enough that it would be unwise to send it through a hand-operated switching mechanism. Hence, the need for the weaker current through the ignition switch.

The stronger current passes to the starter motor where it initiates two separate actions. The starter motor is designed so that the electric current activates a lever, forcing a small gear outward on a spring shaft. When extended, this gear, called a pinion, comes in contact with a toothed gear on the outer rim of a large flywheel on the end of the engine’s drive shaft. This large gear is called the starter ring gear.

Starting an engine: The second action

The second action in a direct current electric motor is the rotation of its central shaft, caused by the larger current passing through the motor. A motor transforms electric energy into the mechanical energy of the central shaft’s rotation. It does this because the electric current interacts with the magnetic field in the starter motor and results in the rotor on the shaft beginning to turn. By the time this turning action reaches the motor’s designed top speed, the pinion at the end of this shaft has already engaged the ring gear on the flywheel. The engine then starts running on its own and the starter’s safety features automatically disengage the pinion from the ring gear. The spring brings the pinion safely back to its resting position and the job of the starting mechanism is done.

When starting, if you hold the ignition key in the “start” position a little too long, you will encounter a problem. Here, too, is a spring that brings the switch back to the “on” position from “start” as soon as you release the key. If you fail to do so, you will hear the evidence of your mistake pretty quickly. The good news is that your mistake is not as bad as it sounds. The safety mechanism in the starter has already released the pinion from the ring gear. The bad news is if you do this often or for any extended period, you may drastically shorten the life of the starter motor.

Rainy Day Refresher

It’s perhaps surprising, but true: Driving on a rainy day is more dangerous than driving pexels-photo-125510on a snowy one. When the rain starts to fall and pavement is wet, your likelihood of a crash is higher than during wintry conditions like snow, sleet and ice, according to data from the National Highway Traffic Safety Administration (NHTSA).

After averaging 10 years of statistics, NHTSA researchers found that 46 percent of weather-related crashes happened during rainfall, but just 17 percent while it was snowing or sleeting. Those statistics are partially explained, of course, by the fact that many drivers have the good sense to stay home during a bad snowstorm, says Debbie Hersman, president and CEO of the National Safety Council, which offers defensive driving courses. But the statistics also reflect a sobering truth, she says: Drivers often do not respect the rain, and fail to adjust their driving habits to hazardous conditions.

Here is how to reduce the chances of being a rainy day statistic, according to safety experts.

Get Your Car Rain-Ready: Tire tread is key, says Bill Van Tassel, Ph.D., manager of driver training programs for the AAA national office in Orlando, Florida. Dig out a quarter (forget the old advice about Lincoln’s head on a penny, as some researchers have found the quarter test more accurate). Insert it upside down into your tire tread. “If part of Washington’s head is always covered by the tread, your tires have more than 4/32 of an inch of tread remaining. If the top of Washington’s head is exposed at any point, you should replace the tires.”

According to NHTSA, tires with 2/32 of an inch of tread are unsafe. However, you may want to replace tires before they get this worn, depending on driving conditions.

  • Tire pressure is important, too, he says. You should check the pressure once a month, using a tire gauge. NHTSA offers many other tire safety facts.
  • Check your windshield wipers to be sure they’re up to the task. If they need replacing and you’re doing it yourself, you can check online guides to be sure you’re doing it correctly.
  • Check headlights, taillights, brake lights and turn signals to be sure all are working properly. When you’re driving, turn on your headlights to boost your visibility. Some states require the use of headlights when windshield wipers are in use.

Slow down: Driving too fast for conditions is especially dangerous on wet pavement because your tires lose traction with the precipitation, Van Tassel says. “When roadways are wet, the friction is reduced between the tire and the road,” Hersman adds. No friction is a bad thing. Tires are meant to grip the roads, not slide on them.

How much does traction decline in wet weather? “You might lose about one-third of your traction,” Van Tassel says. And that figure is why this recommendation makes sense: Reduce your speed by about a third when it’s wet or rainy. If the speed limit is 55 mph, aim for under 40 mph. “That is not a hard statistic but a rule of thumb,” he says.