Do Stop-Start Systems Really Save Fuel?

To answer the last question in our 4-part series “Does the Idle Stop & Go System Really Work?”, Gateway Kia Quakertown PA service department describes the technology behind a stop-start system. To save fuel the ISG (Idle Stop & Go) system automatically shuts down the engine when the vehicle is idle for a period of time. Then, it restarts the engine automatically when the driver performs certain actions. The concept is hard to dispute because an engine doesn’t burn gas when it’s shut down.

This technology began with hybrids. At lower driving speeds, the hybrid electric motor engages and the gas engine disengages. Since the early days, systems that developed into the Idle Stop & Go have been installed in nearly every type of vehicle. This includes heavy trucks and vans. But the theory has yet to sink-in with motorists. They still question whether there’s a fuel saving.


The reason for their questions is a popular belief that starting the engine uses more fuel than an idling engine. Logically, repeated starts will burn more fuel. Kia Quakertown PA service department says this is true, but only under one condition. That condition is starting the engine from a cold start. When cold, the engine will consume more fuel because the onboard computer is programmed to richen the fuel mix. A richer mix burns hotter and warms the engine faster when the outside temperature is cold.

Now, if the “Idle Stop & Go” system does save on fuel costs, the big questions are how much does it save and is the option worth it?


First, as we explained in the previous section of this article, the Idle Stop & Go system deactivates under certain conditions. One of those conditions is when the engine is cold, so the ISG system does not repeatedly start a cold engine, it only engages after the engine is warm. Accordingly, Kia’s Idle Stop & Go system only stops and starts warm engines.

The majority of drivers believe the amount of savings from the ISG system is small, but when you repeatedly save something small, it adds up quickly -like putting loose change in a jar. The engineers who developed these ISG systems report potential fuel savings in the range of 3-12 percent. The extended span from 3 to 12 percent accounts for the diverse driving styles and conditions. For example, motorists who briefly stop at stop signs see fewer savings than those who sit idle at long stop signals. Remember, the longer the vehicle sits, the more fuel saved when the ISG engages.


Using the above points, if your vehicle performs at 20 mpg in the city, there is a very good possibility the vehicle will perform at 22 or 23 mpg with an ISG system installed. However, the impatience that builds from waiting in traffic can undermine savings. While in stopped traffic, drivers tend to move forward at any opportunity, even if only by an inch. So, to keep the system engaged, the driver should resist the temptation to inch forward when they see the car ahead inch forward. Inching along disengages the ISG system and it won’t re-engage until the vehicle passes a minimum speed threshold. Whenever possible, keep the car still until there’s enough distance between you and the car ahead so when you move, you can meet the minimum speed threshold.


Overall, the Kia ISG (Idle Stop & Go) system has become more popular with Kia owners. Mainly because the feature offers the vehicle owner a level of accountability for contributing to reducing the use of fossil fuels and emissions that pollute the environment. If you find these reasons beneficial and wish to see the ISG system in action, then stop by at Gateway Kia Quakertown PA and a Kia customer service representative will assist you.

More from Gateway Kia Quakertown

Does The Auto Stop-Start Drain The Battery?

Is The Auto-Stop Bad For The Engine or Starter Motor?


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