Start/Stop Starter: The Truth About Long-Term Durability
Why Start/Stop Starter Motors Don’t Burn Out Quickly
If you’ve ever driven a vehicle equipped with an engine start-stop system, you’ve probably wondered: “How does the starter motor not burn out with all this constant starting?” That’s a fair question. After all, we were taught that excessive cranking wears out starter motors quickly. But here’s the truth—start/stop starter motor design and construction is nothing like that of a traditional starter. These systems are designed from the ground up to handle at least ten times the number of start cycles without failure.
I know you’re thinking that 10X the number of starts isn’t enough, but there’s more to it than just the number of starting cycles. There’s also the starting conditions to think about. For example, as you’ll see below, the amount of force needed to restart a warm engine is a fraction of the force needed to start a cold engine. So right off the bat, start/stop starters last longer because restarts are easier than cold starts. And, there’s more. Read on.
Built for Abuse: The Unique Design of Start/Stop Starter Motors
Let’s start with the fundamentals. A conventional starter motor in a gasoline-powered car might only be used 1–3 times per day, averaging about 30,000 to 40,000 starts over its expected life. In contrast, a car with an engine start-stop system might restart the engine 30–60 times a day, racking up 400,000 to 500,000 cycles during the vehicle’s lifetime.
Start-Stop Starter Motors Spin at a Slower Speed
In a traditional starter, about 90% of the carbon brush wear happens not during cranking, but during the spin-down phase—when the motor coasts to a stop after the power is cut. That high-speed coast down creates arcing and heat that wear down the brushes quickly.
Denso planetary gear start/stop starter
Start-stop starter motors utilize a planetary gear design to significantly reduce both starter cranking and coast-down speeds. As a result, the spin-down time is shorter, and the brushes experience much less friction and electrical wear. This is one of the key reasons why start/stop starter motors don’t burn out quickly, even though they engage far more often than traditional starters.
In addition, the electrical systems that run start/stop starter motors are designed to bring the motor to a controlled stop, rather than an abrupt power cut-off, reducing shock to the geartrain and improving durability.
Start/stop starters use different brush material and a redesigned commutator
Traditional starters use a carbon brush mounted on stiff springs. Over time, the carbon brush wears a groove into the motor’s commutator. Brush and commutator wear are common causes of starter failure. Start/stop starters, on the other hand, utilize reinforced brushes made of more durable materials, such as carbon composites or copper/metal-infused carbon. The brushes require less pressure to contact the commutator, resulting in less wear.
These brushes can endure hundreds of thousands of engagements without excessive wear. The commutator and armature windings are also built to resist heat and electrical arcing that would destroy a traditional motor.
Beefed up bearings extend starter life
Traditional starter motors typically use sintered bronze, oil-impregnated sleeve bearings to support and center the armature and starter drive. These bearings are made using powdered metal that is compacted under high pressure and then heated to just below its melting point. This creates a porous metal structure that’s vacuum-loaded with oil, resulting in a self-lubricating bearing ideal for small electric motors.
You’ll find sintered bearings in a wide range of automotive
Sintered Bronze Bearing
applications, including your HVAC blower motor, many radiator fans, and almost all power window, power seat mechanisms, and power door lock motors. They’re commonly used because they’re cost-effective and require no maintenance.
However, sintered bearings have limitations. They’re not designed to handle high radial or axial loads, and they perform poorly in cold weather conditions, where the lubricant becomes less effective. These limitations make them unsuitable for demanding applications, such as start-stop starter motors, which require high durability, precise alignment, and reliable performance under frequent cycling and variable temperatures.
That’s why start/stop starter motors use heavy-duty, sealed ball bearings or roller bearings. These bearings are designed to handle the high radial and axial loads, frequent cycling, and elevated temperatures associated with
Sealed roller bearing
constant engine restarts. Sealed ball and roller bearings provide a more precise alignment, lower friction, and significantly longer service life, making them ideal for the demanding duty cycle of start-stop systems.
Heavier-Duty Solenoids
In a traditional starter, the solenoid serves a dual purpose: it mechanically pushes the pinion gear forward to mesh with the flywheel ring gear, while simultaneously functioning as a high-current relay switch to send battery power to the starter motor. This setup subjects the solenoid’s internal contacts to frequent arcing and pitting, which can lead to wear and failure over time.
Notice the beefed-up solenoid on this DENSO TS Starter Motor For Start/stop applications
In contrast, a start-stop starter motor uses the solenoid solely to engage the pinion gear with the flywheel. Power switching is handled by a separate, dedicated control module or relay, not the solenoid itself. This separation of duties eliminates electrical wear on the solenoid contacts.
Because the solenoid no longer has to carry high current during cranking, it requires much less power to operate. This not only improves reliability but also reduces the overall current demand during engine restarts, which is critical for the high-frequency cycling of start-stop systems.
Start/stop Systems Employ Better Current Management
A low cranking voltage can quickly burn out a starter motor. When battery voltage drops below 9.6 volts during cranking, the starter motor draws more current (amperage) to produce the same amount of torque. The increased amperage causes increased resistance in the windings, resulting in excessive heat that damages the armature winding insulation. The high current also causes slower and inconsistent rotation, resulting in arcing between the brushes and the commutator. Arcing pits the commutator surface and shortens brush life.
That can’t happen in a vehicle equipped with start/stop technology because the power management system won’t allow shutdown if there’s any potentential for low cranking voltage during a restart.
Hot Restarts Are Easier on the Starter Motor
Another factor that explains why start/stop starter motors don’t burn out quickly is that most of their activity happens during hot starts, not cold ones. Starting an engine that’s already warm is drastically easier:
• Oil is already hot and circulated, and most late model engines are built with oil retaining bearings, so there’s less internal resistance on rotating parts during cranking.
• The engine is hot, so the fuel evaporates instantly, reducing cranking times.
• The battery voltage is stable because the engine has been running and charging the battery.
All of this reduces the load on the starter motor during each cycle. It’s the cold winter morning starts that kill traditional starters—not the hot, frequent restarts you get in a start/stop-equipped vehicle.
Advanced Battery Support Is Also Critical
You can’t talk about start/stop starter motor life without mentioning the battery. Start-stop systems don’t work well with traditional flooded lead-acid batteries. Instead, they use AGM (Absorbent Glass Mat) or EFB (Enhanced Flooded Battery) types that can handle rapid voltage drops and recharge quickly.
Without that electrical support, even the most durable starter motor would struggle. If your start-stop system stops working suddenly, a weak battery is often the first suspect, not the starter.
Now, the caveats
1) The information in this article pertains to starter motors that engage the flywheel ring gear. Some start/stop systems, especially in hybrids, use an alternator/generator belt configuration. The jury is still out on the longevity of those designs.
2) Engine designers are currently using oil-retaining crankshaft bearings to reduce wear on restarts. While sounding good in theory, there’s some lingering doubt about long-term wear on crank bearings due to lower oil film strength, especially with the low viscosity oils.
3) I don’t use the start/stop feature in my vehicle. It’s not because I’m worried about starter life or bearing wear. It’s because I hate the annoying start/stop cycle.
4) There’s some evidence to show that the expensive AGM and EFB batteries aren’t lasting as long as initially predicted. In that case, a portion of the fuel savings will be lost due to more frequent and more expensive battery replacements.
©, 2025 Rick Muscoplat
Posted on by Rick Muscoplat