Idling or turning off the engine? 3

[pietro82]

Hi all,

I am aware that idling is fuel inefficient and a waste of fuel, but I guess that it is not always convenient to turn the engine off, since the turning on requires more energy than idling. So, I think that for long periods, turning the engine off is more fuel efficient than idling, but not for very short periods. Is there any study or paper that reports when it is more efficient to idle than turning off the engine?
Thank you so much.

Best regards,

Pietro

 

[SuperSalad]

Running an engine is detrimental to the engine's life with regard to time.

Idling an engine is detrimental to an engine's life with regards to miles because you are producing wear without any added miles.

There are more intricacies to each point, but I'd venture a guess that's the talking points what you read were referring to.

Andrew H.

http://www.mototribology.com

 

[CWB1]

Many states here in the US have taxed heating oil to be nearly the equivalent of onroad diesel in cost. Many hobby farmers in my family's locale ran "offroad" fuel in their personal vehicles for years, in recent years most have given up as maintaining tanks and pumps is more of a pain than they see beneficial.

 

[LionelHutz]

In this part of the world, the premium cost of a diesel equipped vehicle is next to impossible for a typical commuter to recoup via fuel savings. The only way to actually save money would be by finding a source of the fuel without taxes as Greg alluded to, but that is not easy to accomplish for the typical commuter.

 

[BrianPetersen]

At idle, oil pressure and flow are at a minimum, valve spring pressure "is what it is" (the springs don't magically apply less force just because the engine is only turning slowly) so the hydrodynamic conditions at sliding-type valve lifters/tappets/buckets are at their worst. If the idling is following a cold start, idling doesn't generate as much heat so the engine takes much longer to warm up. If the engine in question is a modern emission-controlled diesel engine, it will have trouble keeping catalysts up to temperature, so it will probably be attempting to do screwy things with the fuel injection to try to raise exhaust temperature.

Re the valve spring and valve lifter hydrodynamic lubrication situation ... one would hope that the engine manufacturer has sorted this out, but it doesn't always happen. A couple of vehicles ago, I had a 2006 VW diesel (last of the type before the emission controls went crazy), which was an engine type that had electronically-controlled but mechanically-operated individual unit injectors. 4 cylinder 8 valve, thus 2 valves in line with each other per cylinder. They needed an extra cam lobe to operate that unit injector, which forced the lobes for the intake and exhaust valves to be narrowed relative to historic VW 8-valve engines. VW's method of compensating for this was to specify the use of a very specific engine oil. They still had frequent issues with camshafts and lifters - and yet, I put 430,000 km on that car without having that trouble. Part of this is me living in a relatively cooler climate (which keeps oil temp down and viscosity up - better for hydrodynamic lubrication - the issue appears to be more prevalent in hot climates). Part of it is my usage pattern which frequently saw that engine spinning 2000 rpm in top gear on cruise control and hardly any city driving. And I used the right oil. Of course, if you ask VW, they never had any issues with worn-out camshafts and lifters, but I digress.

 

[enginesrus]

Diesel cost? Back in the old days in the US, diesel was always half the cost of gasoline, I remember as a kid diesel at .14 a gallon and gas was around .25 or so(that is cents). It has magically gone up in price, in some areas it can be a few cents or more less cost than gasoline. Depending on the state there are special petroleum taxes so price varies.

 

[dgallup]

The sign outside my window prices diesel at 21.5% more than gasoline almost wiping out any efficiency benefit from the diesel cycle.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[gruntguru]

" diesel at .14 a gallon and gas was around .25 or so(that is cents)"
Holy crap .25 cents per gallon!

je suis charlie

 

[RodRico]

The difference in price between gasoline and diesel is very different in Europe. I have read that the US difference is largely due to the fact that we're awash in light crude (preferred for gasoline) and comparatively low on heavy crude (preferred for Diesel).

Per

https://www.globalpetrolprices.com/...

 

[monkeydog]

Unofficial test on my 2018 Ford F150
V-6, turbo, 10 speed
Location Denver Colorado area
On May 1, I had about 5000 miles on the truck.
I kept the auto-stop turned on, drove in "eco" mode most of the time, with "sport" mode turned on less than 5 times for traffic light starts, then back to "eco" mode.
Total miles for the month of May approximately 1000 miles.
For the month of May 20.7 mpg.

I turned off auto-stop June 1. I will report my mpg after June 30.

 

[gruntguru]

Variations in driving pattern, traffic patterns etc will cause more variation in mpg than the auto stop function.

je suis charlie

 

[RodRico]

You asked for a study, here it is:

http://www.iwilltry.org/b/projects/how-many-seconds-of-idling-is-equivalent-to-starting-your-engine/

. The conclusion is that fuel is saved for idle periods longer than 7 seconds. Since most traffic lights are far longer than that, it would yield an improvement over the long term. The low cost P0 hybrid configuration is sufficient to recapture the energy used in starting. While the focus here has been on efficiency impact, stopping rather than idling also results in reduced emissions (which is why idle emissions are tested in most emissions tests).

 

[VEBill]

Video on the same subject is here:

https://www.youtube.com/watch?v=dFImHhNwbJo

Video mentions the same "7 seconds" as mentioned just above.

 

[michaelwoodcoc]

Honda even does this with their scooters in Japan. The good old nps50 and perhaps some more

 

[monkeydog]

After about 1100 miles on my Ford F150 for the month of June and 1st week of July, I had 21.4 mpg. A slight increase from 20.7 mpg in May.
Same routes, no change to driving patterns, only difference is an increase in AC usage.

 

[Lou Scannon]

Have you quantified your measurement accuracy and repeatability?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[monkeydog]

LOL
"Have you quantified your measurement accuracy and repeatability?"
As I said in my earlier post - an unofficial test.
For my driving habits and routes, the auto-stop/start does not do anything for me.

 

[RVAmeche]

What's your typical route? City, suburban, or rural?

I know in general driving, your mood affects mpg much more than silly things like drafting or turning the AC off. I imagine if you drove primarily in areas with stoplights auto-stop would be more beneficial.

 

[VEBill]

Here's an obvious variable: your local jurisdiction's assumptions about optimum traffic signal light timing.

I've been to quite a few cities in the USA where a red light stays red for minutes on end. Monumentally boring.

At the other extreme, I was just visiting Toronto and I noticed that the traffic signal light cycles there tended to be fairly quick. The rental vehicle had Auto Stop-Start, and it wasn't even getting 7 seconds. Each red light was merely a short pause. Often not even enough time to check the navigation.

YMMV.

 

[monkeydog]

My drive is suburban, freeway and a little city.
My drive to work is a 4 miles one-way, one stop for a right hand turn and one stop to show my badge at the plant entrance. Most driving on the weekends, with every Wednesday evening about 20 miles one way mostly freeway.

 

[RVAmeche]

That route almost entirely removes the use of auto-stop so I'm not surprised the mpg was the same.