Coasting in Neutral or In Gear?

I found plenty of opinions and bad science on this topic but there is no conclusive evidence available to settle this debate.  Which one saves more gas when coasting?  Shifting into neutral or staying in gear?

My philosophy is:  If you can't find someone from which to copy the answer, FIGURE IT OUT YOURSELF! Then write a blog about it.

The Neutral Camp: Shifting into neutral allows the engine to run at its lowest RPM but the engine has to burn a small amount of fuel to keep itself running. Very little resistance is applied to the motion of the vehicle.

The Keep it in Gear Camp: Keeping it in gear, the vehicle's computer senses the reduction in power demand and shuts off fuel to the fuel injectors. When costing in gear, the engine is essentially off. This added resistance acts like an engine break, slowing the vehicle down but it does so with almost no fuel consumption.

Both sides have a valid argument. As I research ways to achieve higher fuel efficiency, I find myself changing sides back and forth. 

Using my newly acquired Scan Gauge II, I am now able to accurately measure instantaneous fuel economy. Since the late 1980's, every single fuel injected vehicle on the planet has had the ability to monitor its instantaneous fuel economy but almost every automobile manufacturer chooses not to include this "planet saving" feature in their vehicles. Why? I don't know.

While driving my wife's 2002 Chevy Venture, I found a less-busy section of interstate where I could setup and run the test.  With the aide of my mom who was traveling with me, I recruited her to assist me in recording the data. 47 years ago, she typed my dad's Masters Thesis.  Mom was more than capable of writing down a few readings while I focused on keeping the van traveling between the lines.

After I accelerated above the desired speed, I let off the gas until the van began coasting. This allowed the van to settle out and decelerate to the correct speed. Note:  All freeway speed measurements were taken on a flat, strait stretch of road during a high wind storm. This unusual weather provided a nearly constant 25mph tail-wind which allowed the vehicle to decelerate more slowly. This aided me in taking more accurate, high speed readings.

Initially, the data was inconclusive. The first 2 sets of data showed that coasting in neutral got better gas mileage. The second set of data points revealed that keeping the van in gear was the more fuel efficient choice.

I decided to try this experiment again later that night, this time running at slower speeds in an undeveloped residential neighborhood. By this time, the wind had died down to only a few mph.  With the aid of my 9 year old daughter, we ran 2 sets of “coast tests” at 30mph and 2 sets at 25mph. Each set was driven in an opposite direction to eliminate the wind as a factor. But once again, the first 2 tests revealed that Neutral is the superior choice and 2nd set of tests demonstrated that coasting in gear was better.  What is going on here?

Glancing down at the Scan Gauge II display, it hit me. Engine temperature!!!

When an engine first starts up, it is running at temperatures that are out of the operating range of some of its sensors. To combat this, the vehicle's control system runs in an "open loop" (does not receive feedback from its sensors) so it plugs in default values for the sensors.
As the engine warms up, the engine's control system switches over to “closed loop” where it makes decisions based on the actual readings from the sensors.

While running with a cold engine, coasting in gear gets lower fuel efficiency and coasting in neutral achieves higher efficiency.  After the engine warms up, the opposite is true. 
Update 5/1/2011:  The effect I was seeing is not related to the closed loop/open loop.  After more tests, my wife's Chevy Venture goes into closed loop within a few seconds of starting up the engine.  Whatever the phenomenon, the increased in-gear efficiency only happens after about 10 minutes of driving and after the engine coolant temperature reaches about 185 F.  I assume it is when the thermostat opens.  Whatever the effect, it is re-producible, predictable and measurable.

The following readings were taken on 3 separate occasions, each while the the engine was cold.

Note:  instantaneous fuel efficiency readings can be extremely high while coasting at high speed. 

Engine very cold in the early morning
75mph run   Gear       mpg
Run#0          Neutral    140mpg
Run#0          In Gear     97mpg

Engine cold in afternoon and very high tail-wind
65mph run   Gear         mpg         RPM
Run#1          Neutral      176mpg     900rpm
Run#1          In Gear      170mpg    1800rpm
Run#2          Neutral      188mpg     914rpm
Run#2          In Gear      186mpg    1630rpm

Engine cold at night and low/no wind
30mph run   Gear        mpg          RPM
Run#3          Neutral      82mpg       769rpm
Run#3          In Gear      69mpg       894rpm
Run#4          Neutral      89mpg       737rpm
Run#4          In Gear      76mpg       878rpm

The following readings were taken on 2 separate occasions, each after the engine had warmed up.

Engine warm ~195 degrees
25mph run   Gear        mpg           RPM
Run#1          Neutral      62mpg        858rpm
Run#1          In Gear      64mpg        875rpm
Run#2          Neutral      63mpg        858rpm
Run#2          In Gear      64mpg        855rpm
Run#3          Neutral      67mpg        814rpm
Run#3          In Gear      69mpg        828rpm

30mph run   Gear        mpg            RPM
Run#4          Neutral      80mpg        858rpm
Run#4          In Gear      83mpg        847rpm
Run#5          Neutral      82mpg        825rpm
Run#5          In Gear      85mpg        792rpm

55mph run  Gear          mpg           RPM
Run#6         Neutral       154mpg       890rpm
Run#6         In Gear       155mpg      1080rpm

70mph run  Gear         mpg           RPM
Run#7         Neutral       200mpg      900rpm
Run#7         In Gear       205mpg      2000rpm (WOW!!)

Conclusion: With a cold engine, coasting in neutral uses 12% less fuel than coasting in gear. (at least for the default values in the computer of my wife's 2002 Chevy Venture). When the engine is warmed up, it flips the other way and coasting in gear saves on average 2.7% more fuel than coasting in neutral.

If you drive a manual transmission and have a short commute (less than 15 minutes), you will be better off coasting in neutral as most of your commute will take place with a cold engine. If you drive an automatic and/or have a commute that lasts longer than 15 minutes, coast in gear. It's probably better to leave it in gear anyway just for the safety and convenience aspects.

I may only be getting only 20mpg while driving 75mph but during that 5 seconds span when I am coasting at freeway speeds before pushing on the gas again, my van is getting over 200mpg.
Using a tool like the Scan Gauge II allows for super accurate measurements of high fuel economy during these very specific types of driving.
Although these short periods of excellent fuel economy make up only a small portion of a normal commute, they contribute to the overall fuel and cost savings.
Now that each one has been quantified, you can now decide which method best suites your personal driving preferences. For a warm engine, there is only 2.5% of variation between the two methods and for most people, that's small enough to say “who cares?” That's fine but at least now we know.

Pimp My Doorbell Button

A newer version of this article is located at my new website at John Saves Energy


Most appliances draw a tiny bit of power all the time in exchange for a convenient or useful purpose. For example, a cordless phone with base station, a TV with remote control or the microwave oven with its glowing clock and fancy Lieutenant Commander Data console touch buttons.

Now don’t get me wrong. Doorbell lights are helpful, convenient and luxurious.  Not only do they pinpoint where the doorbell is located, but pushing the button turns the light off, indicating to the visitor that the doorbell rang inside.  Oooo fancy! 
"But why would I want to aid the Kirby salesman at being able to reach me better"? This is a discussion for a later blog topic, "How to electrify door-to door Solicitors with 24,000 Volts while still keeping little Jimmy and Mrs. Snow (from down the street) out of harm’s way".

When I find that an appliance in my house draws power all the time for no good reason, its gets shut off. For example, the sprinkler timer and A/C compressor during the winter time.
As I near the end of my list of phantom power consuming appliances, I’m starting to look at the efficiency of these devices. Why should a TV draw 20 watts in standby when it could provide the same function drawing less than 1 watt?
One night while turning off the porch light, I noticed that the doorbell light was providing quite a bit of light all by itself. It seemed like overkill that this doorbell indicator was acting more like a beacon of hope for tempest tossed sailors than a doorbell light.

A doorbell is a simple circuit. It has a low voltage transformer that steps 120 volts AC down to about 21 volts AC which then runs through low voltage wiring to the doorbell switch. The doorbell switch has a small incandescent bulb wired across it. The tiny light bulb provides light but has too high of resistance to actuate the solenoid. When the suspecting visitor pushes the button, the circuit is closed, shorting out the light and energizing the solenoid.
The solenoid has a small hammer that compresses a spring and smacks into a "ding" bar, (I just made that up). When the switch is released, the solenoid de-energies and the hammer flies back the other way into a "dong" bar, (ha ha, I’m such a dork). 

During the "ding-dong" sequence the entire circuit draws over 2 amps from the 21 volts AC provided by the transformer. The total power consumption is about 50 watts but only lasts the length of "ding dong", so who cares. 

Even with all my fanaticism, I don’t lose any sleep over a dinky 50 watt ding dong. If someone were to ring my doorbell for ½ a second, 20 times a day, every day for a year, aside from me trying to kill them, the total time spent ringing the doorbell would only add up to 0.5*20*365 = 3650 seconds or ~1 hour per year. At 50 watts, that would only cost ½ cent per year.  

What concerns me is the power draw of the incandescent doorbell light itself. The continual power draw of my doorbell (with light) is about 4 watts. That might not seem like much but if you consider that it runs 24-7 all year long, that adds up to 35KWH annually and costs $3.50/year.
"That’s still not a big deal" you say? Well, saving a little energy everywhere really adds up. After all, "Find a penny, pick it up, all the day you’ll be a scrounge. A scrounge who just made a penny that is".
The heady days of the incandescent indicator peaked around the time of the original Star Trek series. Today the indicator light of choice is the LED. 

My original LED doorbell design started out as a simple white LED with a current limiting resistor. That works okay but since the LED is being powered off of alternating current, it flickers at 60 Hertz. I don’t know about you but that annoys the crap out of me. It might even send poor aunt Edna into an epileptic seizure each time she steps foot on my porch. I must rectify the situation.
I modified the circuit to include 4 diodes and a 3.3uF capacitor. 3.3uF was chosen for exactly 3 point 3 reasons: 

1. I already had one
2. It's large enough that the LED won’t flicker and
3. It's small enough that the LED will go out when the button is pushed.

To my dismay, my circuit caused the doorbell circuit to ring continually with an annoying solenoid buzz.
In Chinese Accent:  "Confucius say: A ding with no dong is dung". 
Adding a 1.8K resistor in series with the rectifier stopped the solenoid from triggering.

For comparison, I measured the current draw of both lights. 
Incandescent Light:  21.8VAC   75mA    1635mW
LED Light:                21.8VAC     3mA        65mW
Less power draw on the inefficient low voltage transformer and less current leaking through the solenoid resulted in even more power saved. The 1.5 watt savings from swapping out the incandescent light nearly tripled into 4 watts when the power consumption was measured on TED.

You may say that 4 watts is a trivial power reduction. That may be true, but the sailors sure are furious. 

Even Coal Is A Renewable Energy Source If You Wait Long Enough!

If you think about it, everything on Earth is solar powered.  All the coal and oil in the Earth came from plants and animals millions of years ago that grew by the light of our sun.  The mechanisms that bring us wind, rain, and rivers are all powered by the sun.  Without the sun, we would not have any energy.  Solar power is the past, present and future of our energy production.  But this is a topic for another day so let's get back on track shall we? 

According to Wikipedia, the total global electric power consumption is 15 TW, (15,000,000,000,000 watts). The potential available solar power is 86,000 TW.  That's almost 6000 times more than we, the people of Earth currently need.  The available wind power is 870 TW and the available hydroelectric power is 7.2 TW.

According to Technology Futurist Ray Kurzweil, the total amount of solar energy being produced every year is doubling every 2 years.  In 8 more doublings, he says that solar power could generate enough energy to supply all our energy needs.

Not to say that he's right or that this will happen, but the stage is being set for a great paradigm shift in the way we power our homes, our cars and for that matter, world economies.  

Solar power alone cannot provide all the world's energy needs. We still need something that works at night and when it's cloudy.

The Eventual world wide renewable energy solution will be solar and wind power with hydroelectric acting as the regulator and battery back up for it all.

There are currently 60 planned or operational pumped-storage hydroelectric stations larger than 1 GW world wide.  These work by pumping water to an upper reservoir during times of excess energy production and releasing it to the lower reservoir during peak demand.  While most of these utilize conventional power plants to pump the water, solar and wind power is the next logical step. 

The Real Cost of Rechargeable Batteries and Electronics

I seems like we hear a lot these days about how much our consumer devices are wasting electricity. “Don't leave your phone charger plugged in! Turn off the TV when not in use! TV's, stereos and cell phones are contributing to air pollution and global warming”. Doom! Scare!! Warning!!

Is this really true?

Some of this stuff makes sense and some just seems kind of off-the-wall to me. In the last few years, the electronics industry has made great advancements in reducing stand-by power consumption of battery chargers and power supplies. A cell phone charger 10 years ago might draw 6-10 watts while one today draws less than 1 watt.

I took it upon myself to calculate and/or measure the energy consumption of some of these devices.

If I may error on the side of overkill, let's assume you re-charge your device's batteries every day and that the battery was completely dead each time you charged it.  Also assume 10 cents/KWH electricity rate. 

Surprisingly, battery operated electronic devises don't cost that much to recharge.

Although insignificant, the cost of just having a AA battery charger plugged not doing anything is $4.30/year. The cost of charging four NiMH AA batteries 365 times is 81 cents.

You will always save energy and money by unplugging an unused charger. Whether that is too large of an inconvenience or not is up to you.

While charging batteries, my X8 AA/AAA battery charger sits on the counter top in the kitchen. It looks too cluttered to leave plugged in and sitting there all the time so it gets unplugged and put away after each charge. My cell phone charger is plugged in by my night-stand.  It is too inconvenient to unplug it every morning.  At the electricity cost of 44 cents/ year, who cares.

To charge an itouch every day for a year will set you back 13 cents. 

An ipad comes in at a whopping 91 cents/year. In other words, don't worry about it.

However, leaving your PC on just so it can charge an itouch off of one of its USB ports will cost you nearly $88/year. Set your PC to sleep when not in use and charge your itouch use a wall charger. You can buy Chinese knockoff chargers for about $3 at http://www.dealextreme.com/. They work just as well as the $29 ones at the mac store.

For hi-drain devices, using re-chargeable batteries vs buying alkaline batteries is a no brain-er.

Charging four AA batteries 365 times will set you back $0.81. The same number of alkaline batteries bought in a Harbor Freight 24 pack would cost you $364.

You Can't Afford to NOT Have Solar Panels

My 6.2KW (950KWH/month average) grid-tie solar system cost me $13,200 after government rebates. You say, "But I can't afford solar panels! That's too much money". What if that cost was rolled into your home loan? A 30 year 5% interest mortgage with $13,200 rolled into it will go up $70.86/month. That's $15/month less than paying for the same amount of electricity at 9 cents per KWH, and you are reducing pollution in the process.
Congratulations! Not only can YOU afford solar panels, but in the process, you will make your electricity bill tax deductible, and keep the price of your electricity fixed for the next 30 years. How's that for saving money?