Essential Tips to Avoid Starter Motor Overheating

When overheating is mentioned, many people think of boiling-over engines. Yet, what about the electrics? Specifically, one of the hardest working electrical components: the starter motor.

WHAT IS A STARTER MOTOR?

Virtually every petrol and diesel engine (mild-hybrids included) possesses a pre-engaged starter motor. Unlike steam engines, even the latest modern internal combustion engines cannot start themselves without assistance. A heavy-duty electrical motor is employed to rotate the engine's crankshaft, until combusting fuel takes over. The starter motor, therefore, is designed to get the engine moving from a standstill.

HOW DO START MOTORS WORK?

On activating the ignition switch to start the engine, the starter motor's main pinion teeth engage with those of the flywheel. The main electrical contact bridge closes and power is sent to the main motor. When the motor's armature starts to rotate, so does the flywheel and, therefore, the engine's crankshaft. Once the engine starts and flywheel speeds rise, power is cut to the motor and the teeth disengage.

HOW DO STARTER MOTORS WEAR?

Being an electrical component, starter motors do not last forever. Eventually, it will need replacing but, in normal use, and provided that it is not damaged by external factors, a starter motor should last for over a decade and 100,000 miles. Eventually,

the internal brushes and bushes wear out, necessitating either repair, or replacement.

Inside the motor unit are several sets of coiled wire, which carry the current. As with any electrical coil, they heat up. This can result in the starter motor becoming hot internally. Yet, as the starter motor is designed to be used for short periods, excessive heat-build tends not to be a problem.

WHAT ARE THE WARNING SIGNS OF A BAD STARTER MOTOR?

The main warning sign is an engine that is either difficult to start, or will not 'turn over'.

WHAT HAPPENS WHEN A STARTER MOTOR OVERHEATS?

When it gets too hot, some internal parts of the motor will start deteriorating.

In extreme cases, the motor will become hot to touch on the outside.

In severe overheating cases, the external wiring insulation might start burning.

SYMPTOMS OF A BAD STARTER MOTOR

Sluggish starter motor operation

Past overheating might have damaged the motor so it cannot operate at its normal speed. Slow engine cranking is a typical symptom. Have your motor checked by an auto-electrician.

The starter motor does not operate

A motor that does not work at all might have a solenoid (pictured), that has failed, due to overheating. You may be able to replace the solenoid without renewing the entire motor.

The starter motor smells bad

A motor that has overheated severely might emit smoke, creating an acrid smell. This situation is likely if the engine starts but the motor continues to run. Switch the engine off and contact your garage, or breakdown provider.

HOW TO STOP YOUR STARTER MOTOR FROM OVERHEATING

However, the solenoid is also vulnerable to overheating and the cause is down to abuse. This small component is mounted on top of the main motor and ensures that power reaches the main motor, as well as enabling the motor pinion to engage with the flywheel.

This can be the result of owner abuse. If the starter motor is operated repeatedly in quick succession over an extended period without sufficient breaks, the windings of the solenoid heat up.

Repeated instances of use in this way can cause the solenoid to heat up so much that the electrical coils burn out and fail.

To avoid a faulty starter motor, it should not be activated more than thirty seconds, before being given at least two minutes to cool. If the starter is activated more than three times in quick succession, wait for longer periods between repeat attempts, so that the pent-up heat can dissipate.

Naturally, an engine that either fails, or has become difficult to start, is a typical cause of starter motor overheating but not the only one. DIYers and garages can use the starter motor excessively during certain maintenance operations, such as bleeding diesel fuel systems after replacing the filter.

Should you find instances of the starter motor overheating while driving, check that a major electrical fault is not causing the starter motor to run continually.

WHAT TO DO IF YOUR STARTER MOTOR OVERHEATS?

If your starter motor stops working, you can check if the solenoid's coils have failed, by checking for an open circuit situation with a multimeter.

Replacing the solenoid in a faulty starter motor should be within the remit of most competent DIYers, so a garage should have no problem. With the old coil removed, note the colour of the paper that is wrapped around the coil. Should you witness charing, as pictured, suspect that the main starter motor may also bear internal overheating damage.

If you're unsure whether your starter motor is overheating, or if the problem persists, contact a certified mechanic to avoid further damage.

FAQs

How long can I run my starter motor before it overheats?

Most starter motors can tolerate being run for up to thirty seconds and given two minutes to cool, before being used again.

Can overheating damage other parts of my vehicle?

An overused starter motor may cause the surrounding electrical cabling to overheat. This could increase the fire risk.

Is an overheating starter motor covered by a warranty?

Much depends on the situation, including warranty small print and any statutory rights you may have. Generally, motor faults that have been caused by abuse, excessive continual use, or wear-and-tear will not be covered by warranties

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