Bottom Line
Modern Trucking Techniques
Idling your truck’s engine
This issue, we’ll talk about the evils of idling and point out some very good reasons to turn off your engine. In part two, we’ll examine devices that provide alternatives to idling and how they work, and we’ll weigh the benefits and disadvantages of using inverters.

by Paul Abelson, technical editor

When I entered the trucking industry back in 1979, everyone idled all the time. Drivers told me you turned your engine on Oct. 1 and didn’t shut it off again until Sept. 30. Diesel was cheap, still less than gasoline. Drivers idled for some very good reasons, and for a few poor ones. Engines were hard to start under the best of conditions. We had been into 12-volt electrics for only a few years, and there were still a number of 6-volt systems on the roads. Rather than risk not starting when it was 10 above or colder, or sometimes when it only dropped below freezing, drivers just let their engines run. In the summer, you idled then, as you do today, to keep the air conditioner going … assuming you had one.

But when daytime highs were between 60 and 80 degrees F, and nights were pleasant, drivers still idled. Why? Because “that’s what truckers do.” Everyone did it, without really knowing why. Modern electronic engines start easily at temperatures as low as 10 to 20 F. For most of us, that covers 95 to 100 percent of our climate extremes. Do we really have to idle as much as we do now?

Today, we know a bit more about the evils of idling. It wastes fuel, adds wear and tear to the engine, and pollutes the drivers’ environment. Let’s start with fuel. As I write this, diesel has fallen to just over $1.40 per gallon. We’ll use that price, but if it goes back up, the impact will be greater. Let’s assume you get 6.5 miles per gallon and drive 100,000 miles a year. In one year you’ll use 15,385 gallons of diesel, costing you about $21,540. Now let’s say you idle 10 hours a day (including waiting time, meals and sleeping) for 200 days a year. At high idle, today’s engines burn about 1.0 to 1.25 gallons per hour. Let’s just use one gallon to be conservative. That’s 2,000 gallons at $1.40, or $2,800. By not idling, most of that could stay in your pocket.

That 2,000 gallons has an effect on fuel mileage, too. If you idled just two hours a day, instead of using 15,385 gallons at 6.5 mpg, you’d burn only 13,785 gallons, for nearly 7.25 mpg. There are drivers getting that kind of fuel mileage today. They do it through a combination of well spec’d trucks, careful driving and strict control of idling. You can easily find out how much you idle by downloading idle time (or having your dealer download it) from your engine control module.

At TMC meetings, the subject of idling often comes up. TMC members have accurate records. The best drivers idle only 10 to 15 percent of engine-on time; the worst, upwards of 60 percent. In our example, at a 50 mph average, we have 2,000 driving hours. The additional 2,000 idling hours equates to 50 percent of engine-on time.

We also know idling subjects the engine to added wear. Engines are designed so all dimensions and tolerances are proper at 195 F operating temperature. At idle speed in winter, temperature probably won’t rise above 165 F. When running cool, more soot loading of the oil occurs, wearing parts. According to TMC Recommended Practice RP-1108, “Analysis of Costs from Idling and Parasitic Devices for Heavy Duty Trucks,” engine wear and added maintenance due to idling will add about $0.85 per hour. Over a 2,000-hour period, that’s another $1,710 of operating cost.

Staying warm in winter, cool in summer

Drivers idle to stay warm in winter. A $30,000 engine is an expensive cab heater, but it has several advantages. Running the engine keeps the coolant flowing through the cab and sleeper heaters, keeping it relatively warm. The engine idling at 1,100 rpm will spin the alternator fast enough to provide enough electricity to run the HVAC blower motors (15 amps or more each) and keep the batteries topped off at the same time. Besides, the engine is there. One comes with every truck. Other devices, like generator sets and fuel-fired heaters, have to be added and cost extra.

Another reason to idle, especially in summer, is to stay cool. Air conditioner compressors are belt-driven by the engine, so if the engine isn’t running, neither is the A/C. Both Espar and Webasto, makers of fuel-fired heaters, have worked with cold storage devices that divert air conditioner output and store it to be released later. The technology, akin to making ice cubes and then blowing air over them, is still in its infancy. True air conditioning requires mechanical or electrical power for the compressor. Fans are electrically driven.

All these reasons to idle can be satisfied by devices already available: fuel-fired heaters, electric heaters, generator sets and secondary air conditioning systems.

Critical reasons to stop idling – your health

Perhaps the greatest reason to stop idling is the effect it has on our collective health. We sleep in our trucks with engines at high idle, 1,000 to 1,100 rpm. That translates to between 16 and 18 Hz (Hertz, or cycles per second). That’s close to the frequency range that upsets our body rhythms and excites our nervous system.

The environment we create in and around truckstops is among the worst anywhere. While there are strict emissions standards for trucks on the road, none exist for idling engines. Truckstop air is loaded with soot, unburned hydrocarbons, carbon dioxide and carbon monoxide. While carbon monoxide levels are not high enough to be toxic, they are enough to slightly reduce the amount of oxygen carried by our blood. And the hydrocarbons and soot may explain why truckers have a higher incidence of illness, ranging from respiratory diseases to cancer, than the general population.

With engines idling all around us, we may sleep, but the quality of our sleep is adversely affected. To my way of thinking, the reasons not to idle far outweigh any benefits from keeping the motor running any longer than absolutely necessary.

Next issue, we’ll examine alternatives to idling. We’ll look at devices that offer the benefits of idling while the engine remains off. We’ll see how heaters and coolers work, what generators and their accessories provide and how they work, and we’ll weigh the benefits and disadvantages of using inverters.

Until then, I hope I’ve convinced at least some of you to shut off your engines when you’re not actually driving, especially now when engines start easily and, at least in some parts of the country, evenings start to cool down.

Paul Abelson is Land Line's technical editor.

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