Is Start-Stop Bad for Your Engine or Starter?

Wondering if Start-Stop is Bad For Your Engine and Starter? The Answers

I’ve seen plenty of debates about auto start-stop systems—some drivers love the fuel savings, while others think it’s a disaster waiting to happen. So, let’s cut through the noise: is start-stop bad for your engine or your starter? The answer isn’t as simple as a yes or no, but after digging into the mechanics behind these systems, I can tell you exactly what you need to know.

Does Start-Stop Wear Out Your Starter Faster?

No. The first mistake people make is thinking that carmakers use a traditional starter motor. They don’t. A start-stop starter is vastly different from conventional starters. They’re designed to handle frequent engine restarts without excessive wear.

Here’s what sets a start-stop starter apart from a traditional starter motor:

• Engineered for more cycles— Standard starters are built for about 40,000 starts over their lifetime, while a start-stop starter is engineered for 300,000-500,000 starting cycles.
• Stronger bearings & bushings— Standard starters wear out due to repeated engagements, but start-stop starters use reinforced bearings and self-lubricating bushings to handle the extra strain.
• Enhanced Solenoids & Armatures— The solenoids and armature windings are built for higher heat resistance and quicker response times.
• Improved Gear Engagement— Many start-stop starters use precision-cut gear teeth to prevent premature wear on the flywheel.
• Rapid Engagement Systems— Some manufacturers use pre-engaged starters, where the pinion gear is meshed with the flywheel before the starter motor spins, reducing wear and making the restart process nearly seamless.
• Gear-Reduction Designs— Instead of a direct-drive mechanism, most start-stop starters use a gear-reduction system, providing higher torque and less power draw.

Start-stop starter motors

Start-stop starters encounter less stress than a traditional starter motor

Once the engine is up and running, restarts are monumentally less stressful on the starter because:
1) After the initial cold start, all subsequent starts are hot restarts. In other words, they’re not cranking a cold engine with cold oil so they draw less power and run cooler during starting than a traditional starter
2) A hot engine restarts much faster than a cold engine because there’s no fire quench due to cold metal.
3) There’s less friction because the bearings retain oil.

Is Start-Stop is Bad For Your Engine

No. Engines used in start-stop applications have been modified to retain or recirculate oil in critical locations to ensure wear-free starts. Here are a few of the modifications

1) Scuff-resistant and oil-retaining bearings— As you know, start-up is very hard on a cold engine because there’s no oil pressure to separate engine components, so you get some metal-to-metal contact. Imagine restarting an engine hundreds of times every day without oil pressure! To combat the extra wear, car makers install scuff-resistant friction-reducing coatings on critical engine parts like bearings. The oil-retaining coatings provide a bit more protection until oil pressure can build. Some car makers are now considering an electrically driven oil pump to keep oil flowing during shutdown periods.

2) Electric cooling pumps and oil pumps— In addition, some car makers incorporate electric cooling pumps to circulate engine coolant, maintaining cabin heat in cold weather and preventing hot spots in the engine during shutdown periods. Many hybrids use an electrical AC compressor to keep cabin temperatures comfortable while the engine is stopped. Some car makers are now considering an electrically driven oil pump to keep oil flowing during shutdown periods.

3) Voltage sensing modules— Car makers also include voltage sensing modules to prevent voltage drops in the car’s electronics systems during the engine crank period. As you know, a voltage drop can be significant during cranking. That voltage drop can cause “brownout” conditions for the vehicle’s many control modules, resulting in erratic operation when voltage drops below 9.6 volts. Voltage monitoring devices may shut down non-critical electrical accessories instantly during start-up to conserve power for the starter motor.

• Oil-retaining bearings— Carmakers use oil-retaining bearings for crank and rod locations.
• Oil recirculating pumps— Some carmakers use electrically operated oil recirculating pumps that operate during long stop periods
• There’s minimal fuel/oil wash from cylinder walls during a restart on a hot engine because a hot engine doesn’t need as much fuel to restart

What Wear Are We Seeing In The Real World?

We’re not seeing the doom-predictions of failed starters and ruined engines. What we are witnessing is a shorter battery life than predicted. EFB and AGM batteries are supposed to last longer than traditional SLI-flooded batteries. But we’re not seeing that because of the extra cycles in start-stop systems.

EFB and AGM batteries in start-stop systems, where the driver is actually using the system, are dying around the 3-year mark. That’s comparable to an SLI-flooded battery but at least one year less than carmaker predictions.

Since AGM batteries cost almost twice as much as SLI batteries, you’ll have to recalculate the savings from operating your start-stop system to factor in the shorter battery life.

Why do carmakers use start-stop systems?

Car makers have switched to start-stop systems because they save gas and are desperate to improve their overall fleet MPG. However, it’s important to note that the EPA doesn’t include start-stop systems when calculating mileage ratings. Those EPA MPG ratings are calculated with the start-stop system disabled. However, starting with the 2017 model year, the EPA began issuing credits to car makers that incorporate start-stop systems in their offerings. Car makers will also receive credits for using more efficient glass and aerodynamics.

How does a car auto start-stop system work?

Start-stop systems (also called idle stop and idle stop and go) have been around since the 1990s, mostly in hybrid vehicles. However, that’s changed. Start-stop is now standard on all late-model cars and trucks.

A start-stop system shuts down the engine during extended idling periods to save gas. How much gas does it save? That depends on the vehicle, but typically 8%-12%. In an urban setting where the driver is engaged in stop-and-go driving, the savings can be as much as 10-12%. But there’s only minimal savings when the car is driven at highway speeds, for obvious reasons. Car makers are advertising start-stop systems as saving around 6%. That’s a significant selling advantage, especially for truck and SUV buyers.

How the system determines when to stop the engine

The PCM continually monitors how you’re driving, considering engine speed, engine temperature and load, vehicle speed, brake and accelerator pedal positions, steering wheel position, and transmission gear selection. It also monitors electrical loads to determine whether you’re using headlights, wipers, AC, etc. By monitoring the current battery state of charge, the PCM can determine whether stopping the engine is right given the electrical load being used.

The instant you take your foot off the accelerator, the PCM makes immediate decisions about whether to stop the engine and when to do so. It may wait until the vehicle is motionless or shut it down the instant your foot touches the brake pedal.

Suppose the battery state of charge is less than 75%. In that case, the PCM will override the start-stop system and prevent engine shutdown because it’s not convinced there’s enough power to run the electrical system while stopped and still have enough remaining power to restart the engine. This is especially true if the driver is using AC with high ambient outdoor temperatures or defrosters and heat during winter conditions.

Most start-stop systems use the starter motor to crank the engine during a re-start, although some car makers also use a two-way generator/starter to assist the starter. Mazda’s “i-stop” system, for example, injects fuel into cylinders that are past top dead center on their power stroke and fires the spark plugs in those cylinders to give the engine an extra “kick” to speed up the start process and reduce starter motor load. Mazda reports that engine restart takes only 0.35 seconds in those engines.

It constantly monitors battery condition to prevent a no-start situation

Car makers never want to be in the position where they’ve shut off the engine with a battery that’s unable to restart the engine quickly. That’s why they’ve moved to more efficient AGM batteries. But these aren’t ordinary AGM starting batteries. They’re built with a much bigger reserve capacity.

Do drivers like start stop systems?

Not really. In a recent New York Times article, reporter Eric Taub interviewed one driver who hates the start stop system in his Mercedes.

“The problem, Dr. Tao says, is that the stopping and restarting is rather intrusive. “You actually feel it restarting,” he said. “In terrible stop-and-go traffic this thing comes on and off constantly. In 20 minutes, you can have 50 stop-and-start cycles. It can drive you totally insane.” New York Times 4/7/16

©, 2016 Rick Muscoplat