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Old 12-26-2007, 10:16 PM   #1 (permalink)
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Pulse & Glide / EOC: Anyone rated their gallons per hour @ 0mph?

So I just started trying out pulse and glide on my 93 Civic DX hatchback and haven't done the final fill to see what my MPG has changed to, but it got me thinking on exactly how much gas my car burns when sitting idle. I travel 35 miles to work in just about 35 minutes and get about 39mpg, so by those numbers I'm going about a mile a minute and use .89 gallons per trip. That makes it roughly .0255 gallons I burn per minute. So it takes my car just barely over 39 minutes to burn a gallon of gas while doing 95% freeway driving and the rest city driving.

So if I leave the car idling for 15 minutes, I could find out roughly how much gas I could save per minute by having the engine not running at its minimum strain. Even going as far as wiring a stop watch to a starter kill to give me minutes I'm in motion and not running to get a good idea of how much gas I'm saving.

Are people already doing this sort of thing?

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Old 12-26-2007, 10:50 PM   #2 (permalink)
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On my 1.6 L I burn .3 GPH at idle in "N" and on the 2.0 L it was the same. In "D" it increased to .4 GPH. I should of put the SG on LPH to get a better resolution.

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Old 12-26-2007, 10:51 PM   #3 (permalink)
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P&G or EOC?

Quote:
Originally Posted by dissimilation View Post
it got me thinking on exactly how much gas my car burns when sitting idle.
My car's engine burns 0.5 litres per hour, fully warmed up @ idle, according to the ScanGauge. That's for a 1.0 L, 3-cyl.

You could extrapolate an estimate for your engine from those figures - though it doesn't scale exactly with displacement & number of cylinders. But it'll get you in the ballpark until a Honda person speaks up.

That said - a question about your technique (to clarify what we're talking about)...

If you're talking about turning the engine OFF where you were previously left it ON while not under load (such as idling while coasting with the clutch in, or the tranny in neutral down an off ramp, for example), that's probably not quite the same thing as pulse & glide.

I'd call that engine-off coasting (EOC).

EOC will save you fuel for sure, but not to the same extent as P&G.
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Old 12-26-2007, 11:55 PM   #4 (permalink)
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I'm guessing that I probably burn a gallon an hour probably more. JK, but if it were true it wouldn't surprise me.

I have a question. My Jeep either shifts into neutral when I let off the gas, or shifts into the highest gear possible without lugging the engine (so that I could be doing Idle engine speed at 40 mph). But Whenever I shift manually into neutral, the rpm's go up from 750 to about 1300 (at around 30) and slowly go down as speed decends. So would letting the tranny do what it's supposed to do be better than neutral to a stop? I think that once I stop at a red light I should shift into neutral to save fuel, but when coasting to a stop, I should leave it in Drive? I also coast farther in drive because my Jeep can Idle after coming from at around 20mph. (it's that 4 Liter I tell ya)
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Old 12-27-2007, 02:56 AM   #5 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
That said - a question about your technique (to clarify what we're talking about)...

If you're talking about turning the engine OFF where you were previously left it ON while not under load (such as idling while coasting with the clutch in, or the tranny in neutral down an off ramp, for example), that's probably not quite the same thing as pulse & glide.

I'd call that engine-off coasting (EOC).

EOC will save you fuel for sure, but not to the same extent as P&G.
I'm new to this, so I'm not quite sure what I'm doing. Here in the coastal regions of California, it's all valleys. So you can find yourself pulsing up a hill and gliding down it, where they lineup pretty well for pulsing and gliding. To be pulse and gliding here with only regard for your target speed will find you downshifting and wasting gas to make it up a hill. There's few stretches on my commute that remain level for any sizable distance. As far as gliding down an off ramp, it's a crap shoot here - city planners in San Diego decided to go for variety. There's many places where ramps alternate as overpasses and underpasses like clockwork, some of those are a straight shot and some have you do a 180, and many have a signal just to get on at heavy traffic times (halting you where you would have gained from the overpass on ramp slope). That was a bit of information, my point was that an offramp underpass is the least significant place to coast on my commute.

Anyway, my current trial into this P&G/EOC world has me targeting 70mph. I'm hitting about 80 and letting it go down to about 60. I know going slower would be more beneficial, but I'll check out that trade off as I go.* I'm not religiously maintaining the target speed due to all the constant changes in elevation and traffic speeds, so I guess I'm just opportunistically EOC and trying to P&G where I find it safe and logical to do so.


*Another argument for the higher speed is that it's hard to retain any constant motion in the slower lanes at peak traffic times, where you can easily pulse to the fast lane and just merge to the right once or twice as you glide (we're five lanes wide nearly the whole stretch). If you were doing this in the slower lanes, you'd come to nearly a stop (if not a complete stop) very often. Luckily I go the opposite direction of heavy traffic, so coming to a stop on the fast lane only happens when there's an accident.

Last edited by dissimilation; 12-27-2007 at 10:33 AM..
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Old 12-28-2007, 10:12 AM   #6 (permalink)
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Well, I did a fill up last night just a few tenths short of traveling 150mi according to the trip odometer. I had hardly used a third of the tank and the suspense was killing me to find out what my recent driving habits had gained me. So here's what I got...

149.6 mi
/
2.677 gallons
----------
55.88mpg

That's a bit shocking over the 39mpg I steadily have gotten in the past. Also, I didn't start experimenting with the engine off coasting until I had rolled past 65 miles on the trip, so only 56% of that fillup benefitted from my changed driving habits. This still seems abnormally high, so I'm reserving my enthusiasm and am doubting that I actually topped off the tank completely (it's just too good to be true). Still, there had to be some gain - and I'm excited to verify that my habits are really paying off.

Last edited by dissimilation; 12-28-2007 at 10:15 AM..
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Old 12-28-2007, 10:32 AM   #7 (permalink)
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From your description, you're doing genuine P&G. And based on that, I'm not at all surprised to see 55.9 mpg vs. 39.

When I compared engine-off coasting vs. "normal" conservative driving in my car on an urban loop, I saw a 12.9% gain. My fuel economy went from 50 mpg to 63 mpg.

Knowing what I do now, had I repeated that test loop a third time using dedicated P&G rather than just "opportunity coasting" EOC, I would have seen numbers in the 75-90 mpg range.

Normally I would question the effectiveness of P&G at the very high freeway speeds you cite (80-60 mph), and I'd want to see the results on instrumentation at the time rather than just at the pump. That said, if there are hills involved, and if you're benefitting from the "corridor effect" of air movement within a stream of traffic, those speeds may just be working for you.
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Old 01-05-2008, 05:31 PM   #8 (permalink)
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MetroMPG:
Thanks for the info! I really appreciate all the help and knowledge you lend. It's good to get clarification on the vocabulary of what I'm actually doing. As a newbie I'll throw the word "drafting" out to loosely describe following an SUV about 200-300 feet off, and not realize the true meaning/practice. As for investing in the instantaneous instrumentation, I'll move on to after I've seen what I can do with what the factory gave me and see what eccentric cravings I have afterwards
(there's also the consideration of whether I can get better milage in the geo 'vert or the civic hatchback, which will decide which should be my daily driver and warrant the extra investments and labor)



Well, the New Years vacation break hit since my last post. My wife and I got out of town for the weekend and I didn't get to practice my new driving habits much on the trip. We were pressed on time to make it from San Diego to Modesto to visit family, traveling over 430 miles in about 6 hours (while taking the hit of LA traffic in between). Tssk me as you like, but when a 91 year old widowed Great Aunt is waiting up late for you on the other side with a meal prepared - you put your foot in it. I did get in some engine off coasting over the Grapevine (AKA the Tejon Pass, a 4000 foot mountain range that separates LA from the San Joaquin Valley). On the way down I got a surprise when my brakes lost power. Since then I have learned what a vacuum booster is and how it temporarily provides power to the brakes when the engine is shut off. Between the Grapevine and the 7,000 foot climb/descent to the Sequoia National Forest, I had some extreme examples of coasting that gave me time for experimentation to figure out just how much power the brake booster will provide.

Now that I've been back in town and back to normal driving, I've refilled and I'm out to see just how high a milage I can do on one tank. The needle has hardly gone below the F (full) point on my gas dial and I've already put just over 100 miles on the tank. I have been noticing that I can do far more coasting heading home from work than I do heading to work. I'm going to borrow my Dad's old altimeter (from his old piloting days) to see exactly what the elevation change is and see if that instant knowledge can help me in planning my coasting. What goes up, must come down... and if I can guesstimate my potential energy when traveling through less familiar valleys - it may help me in planning my EOCs by knowing just how much I gained. Fun stuff! I definitely have been noticing when I take repetitive and familiar routes in my car I can be very accurate in my EOC and P&G timing, where I have a whole lot of practice to do to get such accuracy on unfamiliar roads.
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Old 01-05-2008, 05:56 PM   #9 (permalink)
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Quote:
Originally Posted by dissimilation View Post
On the way down I got a surprise when my brakes lost power. Since then I have learned what a vacuum booster is and how it temporarily provides power to the brakes when the engine is shut off.
Did the vacuum go away because you were tapping the brakes here and there, or did it lose it over time with no braking?

I hope you also learned that you can still stop without assis - you just need to put your leg into it much harder. I'd recommend trying that sometime too - purposefully depleting the vac reserve on an empty road/lot and doing a couple of rapid stops. Just FYI.

Quote:
Now that I've been back in town and back to normal driving, I've refilled and I'm out to see just how high a milage I can do on one tank.
Woo! That's the spirit.

Quote:
Fun stuff! I definitely have been noticing when I take repetitive and familiar routes in my car I can be very accurate in my EOC and P&G timing, where I have a whole lot of practice to do to get such accuracy on unfamiliar roads.
Just like a race car driver will have lower lap times on a familiar track. Knowing the road helps immensely.

It is satisfying, with some practice in this style of driving, how you can develop the ability to look down a grade or a stretch of road towards a stop and are able to judge just when to get off the power to coast to a stop at the right spot.
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Old 01-05-2008, 07:29 PM   #10 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Did the vacuum go away because you were tapping the brakes here and there, or did it lose it over time with no braking?

I hope you also learned that you can still stop without assis - you just need to put your leg into it much harder. I'd recommend trying that sometime too - purposefully depleting the vac reserve on an empty road/lot and doing a couple of rapid stops. Just FYI.
It was tapping here and there, the grapevine is quite a massive slope with many turn offs for overheating uphill and many truck runaway ramps going down. I get about two hard brakings in before the vacuum needs to be recharged by the engine. I'm no stranger to braking without the assist of power through different vehicles I've driven over the years, so I didn't panic - but it did certainly get me nervous on something as treacherous as the descent of the Grapevine. Once the initial shock wore off, I turned back on the engine and realized the correlation to something that gave me braking power being charged when the engine was running (and read up to find the name of that something when I got home). I'm interested in seeing if there's a cheap way of putting a pressure meter in place to give me a good idea of what braking power I have.

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