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Is Engine Idling Bad? Brian Dziuk | May 3, 2016 12:09:19 PM

In a lot of the posts on this site, we discuss how using a GPS vehicle tracking system can help you keep drivers on-task and prevent excessive idle time. We frequently state that excessive idle time is a waste of not only your labor time for drivers and work crews attached to a vehicle, but that it consumes fuel and puts extra wear and tear on your fleet vehicles.

But is a little idling really all that bad? What does engine idling really cost you, in the long run?

Let’s find out.

What is Engine Idling? 

Engine idling occurs when a vehicle's engine is left running even though the vehicle is not moving. 

What Wastes More, Engine Idling or Restarting?

Engine idling has got to be better than having to constantly turn your engine on and off whenever you have to stop and wait for a bit, right? Wrong!

Studies have shown that idling for more than 10 seconds actually uses more fuel and emits more CO2 than turning off and restarting an engine. So, when taking short stops, it makes much more sense to turn the vehicle completely off then back on when you are ready to continue your tip. This minimizes both fuel use and CO2 emissions!

Why is Idling Your Engine Bad?

Fleet managers are constantly worried about making the most of their limited budget, and managing maintenance and fuel costs are a huge part of this. Engine idling can negatively affect your maintenance scheduling and fuel consumption, directly impacting your budget as well as the environment. How?

For every two minutes of idling, your vehicle could have traveled one mile, and these "ghost miles" will still accumulate on an idling engine. According to a study, "Excessive idling can create engine wear and carbon soot buildup in the engine and components." This can lead to shortened life of motor oil, spark plugs, and exhaust systems, which means you'll have to replace those materials sooner than anticipated. Plus, putting unnecessary miles on your vehicle means you'll have to conduct routine maintenance such as oil changes and tire rotations sooner than anticipated as well. This can drastically impact your maintenance budget, leaving fewer resources for other aspects of your business.

Plus, preventing engine idling can help minimize the amount of fuel that is being wasted in your fleet, and therefore the amount that you are spending on gas. An idling car uses between 1/5 to 7/10 of a gallon of fuel an hour, and an idling diesel truck burns approximately one gallon of fuel an hour. With average U.S. prices for diesel fuel topping $3 per gallon, that's about $3 an hour wasted on unnecessary fuel expenses.  

When you waste gas through engine idling, you aren't just throwing money down the drain—you're also expanding your carbon footprint. In fact, for every 10 minutes your engine is off instead of sitting idle, you'll prevent one pound of carbon dioxide from being released. Since carbon dioxide is a primary contributor to global warming, minimizing engine idling, and therefore the amount of carbon dioxide your fleet is releasing into the environment, helps to create more sustainable and eco-friendly business practices.

What Engine Idling Really Costs You

Now that you know some of the negative effects of engine idling, what can they really cost you? There are numerous hidden costs of engine idling—here are two major ones.

1. Fuel Consumption During Idle Time

First, let’s start by taking a look at how much fuel a vehicle consumes per engine revolution.

Keeping an engine running, even in idle, requires some fuel/air mixture to be combusted to provide power to the vehicle and keep it ready to move on a moment’s notice. The exact amount of fuel consumed with every revolution, and the number of RPMs needed to keep an engine running in idle, will vary based on the make and model of vehicle in question.

To keep things simple, let’s use an example of an idling engine for a personal car found on Quora. Here, the writer assumes a car with an engine displacement of 2 liters and an engine speed of 700 rpm, (which is 350 cycles/min for a 4-stroke) running “at sea level on a standard 15° C day” where the “volumetric efficiency is 100%.”

According to the calculations given in the article, the resulting fuel consumption is “0.32 gal/hr” for a 2-liter engine. Note that this figure relies on a lot of assumptions, and your own fleet vehicles may have a much higher fuel consumption rate when idling, or even a lower one if you have extremely fuel-efficient vehicles.

For now, let’s assume that your idling vehicles burn about 0.16 gallons of fuel per hour for every liter in their engine displacement. So, using this figure, a 13-liter semi-truck engine would burn about 2.08 gallons of fuel per hour when idling.

2. Cost Per Hour of Engine Idling

According to the AAA Fuel Gauge Report, as of 9/3/19, the average cost of regular gas is “$2.573” while the average cost of diesel fuel is “$2.929.”

So, if you have a non-diesel vehicle with a 4-liter displacement, an hour’s worth of engine idle time would cost you 2.573 * 0.64 = $1.65/hr (penny rounded up). A 13-liter semi-truck using diesel fuel would cost you 2.929 * 2.08 = $6.09 (rounded up).

This might seem like it isn’t much, but how much time do each of your vehicles spend in idle each year, and how many vehicles do you operate?

If your vehicles spent an hour each day in idle, that could cost you a lot of money each year that could be better spent in other places.

Add to this the expense of the labor that is effectively being wasted when your fleet vehicles are idling, and the cost of idle time per vehicle can skyrocket.

Ways to be Idle-Free

While your drivers may not be able to avoid keeping a vehicle's engine running when stopped at a traffic signal or stuck in slow-moving traffic, there are numerous other times when idling is unnecessary and ways that it can be prevented. Here are a few tips for making your fleet idle-free. 

1. Turn Off Your Engine if Waiting More Than 10 Seconds.

Contrary to popular belief, restarting your vehicle does not burn more fuel than leaving it idling. In fact, idling for just 10 seconds wastes more gas than restarting the engine. For example, your drivers should not leave a vehicle running in the parking lot while they run an errand or pop into the store to get a snack.

2. Prevent Unnecessary Idling with GPS Tracking

While some idle time is inevitable because of things such as traffic lights, it is important to avoid unnecessary or excessive idling. This is something that GPS tracking for fleet vehicles can help with.

With GPS tracking software for your vehicles, you can track driver activities, keeping a log of how drivers are using their vehicles on the job. From here, it’s possible to spot bad habits such as excessive idling, giving you a chance to address the problem.

Of course, not all idling is the result of bad driving habits. Sometimes, traffic jams occur that can trap drivers in place without giving them the freedom to simply kill the engine to save fuel. It’s possible to reduce engine idle time by finding alternative routes when your driver’s original path is blocked by heavy traffic, giving you the ability to reroute drivers away from clogged highways and onto routes that will keep them moving forward.

You may find that, over time, the productivity improvements and reduction in idling can more than pay for the cost of a GPS tracking system. If you want an accurate measurement of how much fuel each of your vehicles consume when idling, some GPS units come with diagnostic systems that can monitor key engine performance statistics.

Ready to minimize engine idling in your fleet to experience cost savings and more environmentally friendly business practices? Reach out to a Rastrac expert today!

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