Using Instantaneous MPG indicator to control gas usage

Maintenance/Repairs
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21

That’s the curious thing about the RDX and perhaps the reason why it’s not rated a BestBuy car. I believe the AWD is always engaged as opposed to only being used when needed, but I could be worng. I’m still learning about the car. For 2010, Acura is making this model available with front wheel drive only to improve the gas milaege usage.

But the RDX drives like a dream. And the handling is amazing. Once StrongDreamsWaitHere suggested to research hypermiling, I read more about it on the web. That matches closest to what I’ve been doing. I have noticed an increase in AVG and TOTAL MPG when filing up my next tank of gas.

I paid even more attention to my driving technique going home last night and this morning and I am confirming that even though I can sense the need to increase or decrease my throttling, it does not change my maintained velocity to a point it is a nuisance to other drivers around me. A driver just learns to understand this about his/her car… if they pay attention to it.

Look - I’m not here to fight with anyone. I’m very grateful for the constructive comments because I did learn some things. And if I hurt someone’s feelings about their perpetual machine comment (which was not even something I EVER proposed I was doing) then you should have enough emotional intelligence to just say you assumed wrong. But you commented further that the laws of physics need to be change? I feel that’s really where all this banter started from. Please take into consideration that if you tell someone’s assumption is wrong based on your own opinion… then you are also accountable for what you say. I won’t get into semantics, but just look some of the negative feedback. There’s no basis to assume I perform shenanigans on the highway… even after I’ve said over and over I have noticed to maintain velocity when using this technique. And yet you repeat I annoy other drivers. So, I get irritated when people (even geeks and driving enthusiasts) don’t read well enough to process the facts of the forum.

I do apologize for my typos. I type pretty fast and there’s no spell check on this thing. I do believe that some of my strongest negative responders are intelligent as well… But like me, they get their feelings hurt and they dumb down the forum by responding the way they did. So if you need a hug let me send you a virtual one. And lets get on with discussing this fascinating topic. I researched the archives and have not found one to match this.

Thanks -ldpasion

22

One more comment I’ll make about this topic: I’m not an extremist. Just because I said hypermiling was the closest description to the technique I’m using, I don’t want someone out there to ASSUME I’m trying to accomplish 50mpg or higher, driving a performance SUV. I said in my original post that I have been able to achieve up to 23-24mpg. And on something that is formally rated at 17mpg, that’s pretty darn impressive to achieve!

This is my first forum that I’ve participated in. I have since read many others relating to using this technique to save gas on mileage, and you know what? I’m deducing that many forum participants (the repeat ones) have the same ego issues… You seem to always assume that you are concluding correctly and make extreme judgements on the issue. And that’s what I take exception with. That’s what I mean by requiring emotional intelligence to have pragmatic conversation. Get clarification on something before you make assumptions. We have that extreme problem in this country… there is not enough critical thinking before one opens their mouth.

23

Look, just give up. We’re not going to tell you that your brilliant scheme is genius because it isn’t. Start critically thinking about your own technique. Read a physics book. It will tell you that it will ALWAYS take more energy to accelerate a given amount than you regain by decelerating that same amount, whether its 1mph or 20, and whether its a car, a boat, a plane, or walking. If you gain more on deceleration its because you’re adding energy from other sources, like on a down hill.

YOU said that you accelerate and slow down for this technique. You said that many times. Maybe you’re not perceptive enough to notice what you say you’re doing when you’re doing it, but other drivers are, and want you to hold a steady speed. Constantly changing your speed, as YOU said you do, is annoying and potentially dangerous.

I know you think its awesome that you’re getting 24mpg out of a 4 cylinder car. Sorry, not impressed. My 6-cylinder TL is rated at 18/26mpg and I routinely get 25/34 out of it, and I don’t even use your brilliant technique. And btw I had a loaner RDX for 2 weeks and was getting 22mpg around town, again without “pumping the gas throttle intermittently.”

The only ego issue I see here is yours. You came on here wanting us to all flock around you and tell you what a brilliant soul you are for coming up with this amazing technique that doesn’t work. Presumably we were all to stare, mouths agape, at your apparent ability to flaunt the laws of physics. And while we were at it, we were also supposed to tell you that you weren’t doing any long-term damage to your car at all. And anyone who said otherwise got argued with, and was told they have ego issues, and has limited emotional intelligence, and likes to turn the conversation negative.

I’ll be nice and blunt here: You’re wrong. You’re wrong about the technique working, and you’re wrong about not causing premature wear. That’s not my ego talking. That’s the laws of physics (I know, I know, you want to pretend they don’t apply to you) and common sense talking.

You’ve been wrong from the beginning and no amount of whining about the negative energy around here is going to make you right. But hey. Keep doing what you’re doing. And when you pop your turbo long before it should wear out, or the guy behind you runs into you because you keep changing your speed without changing your speed, maybe you’ll finally learn that what you’re doing is stupid. Probably not, though.

Next time you decide to wander on to a forum populated by people who actually know about cars, it might behoove you to learn something yourself before telling us all how wrong and immature we are.

24

OMG… you are nuts, mister. There’s no need to argue with a person like you who needs to be right, because you’ve even made assumptions about drivers around me… which you have no data on. Thanks for your contribution and hope you have a nice day.

25

“You have no priviledge in knowing how safely I drive to make such an idiotic advice.”

I don’t need to know how safe a driver you are to be able to say that you, like any other human being, can drive even more safely with less distraction.

You can even save gas by watching several cars ahead and anticipating slowdowns and red lights.

My Matrix is rated 33mpg highway, but I get as high as 38mpg just by taking it easy.

26

Thank you circuitsmith, for your 2nd response. It made a lot more sense than your first response below, which wasn’t necessarily measurable.

“I think you should drive gently, watch the displays less and the road more.” -circumsmith

Again, my issue with assumptions with responses. I think one could balance watching displays and the road properly to be a safe driver, as I believe I am. But I do commend you for taking the high road inspite of my initial idiotic response to you. For that I owe you an apology & give you credit for moving on with some real mpg figures.

I’ve driven a Matrix S and though I think it a good car as well. I’m not as impressed with it’s ride and handling as the Acura RDX. They’re not even in the same class of refinement. Although we are discussing gas mileage, I just don’t feel the two cars are equal when it comes to drive experience. I’m glad you get really good gas mileage with your Matrix. Is yours a 2wheel drive or real time AWD? There’s a difference in gas consumption, objectively before taking the way you drive into account… gently or not.

I’ve accepted that higher end cars will normally consume more gas per mile relative to the middle range models. The BMW3 and Infinity EX35, which I have also driven, are comparable to the RDX with similar (or just a little bit better) mpg ratings. I still think I got a better value for my RDX. I just wanted to discuss the thoughts of using the instantaneous mpg inicator. I’m not sure all of us are experts here… otherwise we can formally be paid for our responses. I’m just trying to be careful about information some in here have manipulated. Thanks!

27

In my opinion, the “hyper-miling” or “pulse and glide” techniques are just myths. I’ve driven a Prius for 5 years now and I’m also a long-distance cyclist. Any cyclist will tell you the best way to conserve energy is to avoid unnecessary changes in speed. You don’t need to drive slow, but you do need to drive with your head up and get your foot off the gas as soon as you see the light turn red. You will never be able to maintain your momentum if your eyes are glued to the dash and you don’t see red lights or tail lights until the last second. If you get good at it, you can hit the light just as it turns green without even stopping. The computer mpg of my car is optimistic by about 3%, my other car is off by 10%. The only way to figure this out is to save your gas reciepts and keep accurate records of your mileage at fill-ups.

28

Most drivers save considerable gas on long level roads by just turning on the cruise control. It “pumps” very gently to keep the car running at an even speed.

On up and down hill roads, however, the cruise will tend to “overshoot” and use more gas than a trained foot.

Agree with VDC, unnecessary pumping will make you use more gas rather than less on a straight, level road. Also agree that this pumping will cause unnecessary wear on the turbo.

29

Pulse and glide does work, at least in some cars under some circumstances. If there was no such thing as friction or wind resistance and engines were 100% efficient, it would take the same amount of energy to travel the same distance no matter what speed you drive. But driving in the real world, engines are only 25-30% efficient, and they may be more efficient at one speed over another. If you drive distance D at a constant speed, you will use X amount of fuel. If you drive 1/2D under acceleration you will use 1/2X + Y fuel, where Y is the acceleration premium, and if you coast for 1/2D and your engine has DFCO, then your fuel use will be zero. So whether pulse and glide works depends on how efficient your car is. (If Y<1/2X)

To say it another way, if you get 30 MPG on a straight flat road at constant speed, pulse and glide will work as long as you get more than 15 MPG on the acceleration phase, assuming your acceleration and coasting phases are the same length (in distance, not time) and assuming that your computer cuts off the injectors during the coasting phase.

I would never do this personally, and I think that constantly accelerating to 75 mph and then coasting back down to 55 mph on a highway is a good way to get in an accident, but it’s not ruled out by the laws of physics.

30

“I’m not as impressed with it’s ride and handling as the Acura RDX.”

Well you shouldn’t be considering how much more the Acura cost.
Mine is a 2006 2wd with a 5-speed manual.
I never intended to directly compare the MPGs of the two vehicles.
They are in different classes with greatly different weight and engine size.
My point was that I can exceed the EPA rating without heroic measures.

Besides, you would never try this with your luxury vehicle:

http://mysite.verizon.net/tbrown59/jpg/IMG_3493s.jpg

http://mysite.verizon.net/tbrown59/jpg/IMG_3496s.jpg

31

Pulse and glide may put OP into an early grave. Mileage freaks are becoming a menace to smooth traffic flow. We had a post on this before, and several “diehards” or soon to be, said it was their “inalienable right” to drive any speed they wanted below the posted minimum.

My advice to Idpasion is to drive normally, and enjoy a long and happy life. Your loved ones won’t appreciate all those gas savings when they put you to rest.

32

I fully agree. There is a well known black Prius around these parts whose driver seemingly is hell bent on extracting the most of distance out of a gallon of fuel.

The last time I encountered this person he was traveling at 35 MPH on a two lane road that has a 45 MPH limit, and which traffic usually runs about 45-50 MPH. There are no passing zones. The 35 MPH wouldn’t be terrible, but this assclown will let his speed drop to around 15 MPH on the uphill parts, he is unwilling to even try to maintain his speed whilst going uphill, yet will he will not let his speed go over 40 MPH on the downhill bits either. Myself, along with about 12-15 cars stacked up behind him were forced to follow this fool for 8 miles. Granted in the grand scheme of things it’s not a big deal, but it is very annoying.

The funny thing is that I’ve met 3 people who knew the exact car I was talking about when I mentioned the encounters to friends. If you want to practice fuel efficent driving techniques, that’s fine, but do it when there’s little to no traffic on the road. If you’re hypermiling and you notice a 12 deep line of cars behind you, park the hypermiling and drive according to the prevailing speeds.

33

Used to be when a person was driving a slow vehicle on a 2 lane road they would periodically pull off to the side and let others pass.
People are so self-centered these days.

Ironic that that Prius driver probably save about as much gas as a big SUV would by driving at 69mph instead of 70mph.

34

There are a lot of factors other than engine size that determine a vehicle’s mileage.

35

Manually calculate your mileage and compare it to the computer MPG; i doubt they will be the same. More pumping/heavy foot acceleration/hard braking will cause parts to wear out sooner compared to applying gentle pressure on the throttle/brake. But who wants to drive lame all the time? Drive it the way you want it and fix it when it breaks.

36

One can’t compare the physics of the human body to that of an internal combustion engine. An IC engine is most efficient at nearly full load, and it doesn’t get tired!

Pulse and glide works because it replaces some time period of running the engine under light load at a road-speed rpm with periods of heavier load (more efficient) followed by periods of no load (if fuel cut-off occurs), or extremely light load AND low rpm - coasting. [Pay attention, Shadowfax! : >) ]

Most vehicles need ~ 12 to 16 HP to maintain constant 50 mph with no headwind. (Not sure about the efficient hybrids.) Of that, roughly 9 - 12 HP is needed to overcome wind resistance, ~ 2 HP to overcome drivetrain losses, and ~ 1-2 HP to spin the engine as a vacuum pump. (A closed-throttle engine is essentially a big vacuum pump.) It’s this last factor that pulse and glide reduces, and you can do the math to estimate the potential improvement in mpg that may be possible.

Coasting is more efficient than light throttle in-gear because while coasting, engine RPM is essentially at idle, which minimizes engine pumping loss. Coasting is more efficient than fuel cut-off because it doesn’t use vehicle inertia to spin the closed-throttle engine at road-speed RPMs.

However, if one wants or needs to reduce speed (for example, approaching a traffic light that’s just turning red), then it’s more efficient to keep the car in gear and in fuel-cutoff mode while reducing speed approaching the light.

I doubt any of these methods are practical except with a manual transmission, and they’re most practical when traffic density is very low. But under those conditions, it can be done safely because it doesn’t require taking eyes off the road to watch a gauge, or confuse or inconvenience other drivers.

In general, paying any attention to fuel use is likely to reduce consumption somewhat, with the net effect of developing safe habits that to reduce fuel consumption… …without tailgating, Mr. Prius.

Cars with Bosch DME have had fuel cut-off since at least 1982; I suspect almost all do today. No US BMW has had a vacuum gauge since at least 1968; but since the advent of DME they’ve had a computed MPG display. And since the late 90’s, there is provision to adjust a computational factor so the displayed average MPG can be made to equal measured MPG. My car needed a 5% correction (reduction).

37

"But to really make this work you need a scan tool or something to tell you when your injectors are turning on and off so you will know the best speeds to start and stop"
Well, with the instant MPG display, you can tell pretty well when the injectors are off – on the Caddy the max MPG was 70, if you’re coasting it goes up to 70… if the max is 99 it’ll show 999… if that Acura only shows a max of 40, when the injectors are off it’ll show 40.

 Pulse and glide sounds like the technique you're using.   It does work on a track, does it work usefully on a real road?  I don't know, it would drive any other traffic on the road mad so I have not tried it.  In a vehicle like my Buick, it runs the engine at very low RPM (1000-1400 in town is typical) when cruising, but if I so much as twitch the throttle, it unlocks the lockup torque converter to avoid feeling a bump from the drivetrain, and my RPMs go up to closer to 2000 RPM.  So I think in my case pulse and glide would not save fuel.

 Regarding decel fuel cutoff -- this isn't that new, depending on what vehicle you have -- GM's been doing it since the mid 1980s at least.  Some car cos didn't implement it until recently I guess.   The main vehicles you won't find it are stick shifts -- with the fuel off the engine would stall when the driver put in the clutch.  

 Regarding the low MPGs -- this is true on a lot of US-spec vehicles.  The tendency has been to work over the V6 and V8s for very good fuel economy, with a nice tall cruising gear or two.  The 4?   They'll tune it for higher power per liter at the expense of mileage, and give it low gears to help acceleration.  Result?  I've seen loads of cars where the 6 or even the V8 is tuned up so a 4-cylinder in the same car only gains like 1-2MPG.  (Turbos and superchargers change this but I bet it still applies, the turbo 4 will be making far more power per liter than the supercharged V8, at the expense of MPGs.)   This has been changing with the last year, finally some vehicles have a 4 that might trade like 5HP to get far better MPG than it did a year or two ago.
38

Sorry to disappoint, but pumping your accelerator is not saving you any gas. It is the careful acceleration that is saving the gas. “Instantaneous” mileage is a relative term. With an engine turning at 2000 RPM, your crankshaft is rotating 33 times every second. In a six cylinder engine, that’s about 48 injector events per second. The flowmeter that is reporting to your instantaneous gauge isn’t trying to report in microseconds, but to show you the effects of rapid versus steady acceleration.

Pumping on your pedal has your mind on the wrong thing, and could interfere with your reaction time if you need to stop suddenly. I suggest that you quit doing that, it’s dangerous. Besides, it interferes with your texting, eating your hamburger, talking to the kids, and rubbernecking. Just drive normally and don’t accelerate too fast. If you want to experiment with gas mileage, do it on the highway by bumping up your cruise control a little at a time and taking note of the result. If you REALLY want to experiment, get a ScanGauge II and plug it into your OBD II port. This will not only give you instantaneous mileage, but will show you torque loads, ignition advance, fluid temperatures and so on. Then you’ll learn something about inertia, momentum, and other interesting physical principles.

While I have you all here, I want to suggest another experiment: After you’ve driven a ways on the highway, set the cruise control on a level stretch and note the MPG, or GPH of your instantaneous mileage. Then get off at an exit and buy some fuel with ethanol in it. Drive for thirty miles or so and watch in horror as your mileage drops by as much as 20% (assuming, of course, that you had regular grade gasoline in it before; if you had ethanol in it, reverse the process). Ethanol is being marketed to the environmentally conscious as a clean fuel that’s good for the environment. Nothing could be further from the truth. Ethanol contains 60% by volume of the energy in regular gasoline (look it up, 20,000 BTU vs 12,000). By the time you go the same distance with ethanol you will have burned 175% as much fuel. Which is why they only mix it with gasoline in small quantities, so that you are less likely to notice. Besides actually sending MORE CO2 into the atmosphere, you’re actually paying more for gasoline. If someone sold you a bottle of beer with 10% water in it, you’d probably complain—well maybe not, if they told you it had fewer calories, so it was better for you then and you could drink even more. But if you had any SENSE, you would complain. And no, it’s not a mistake that 10% ethanol will diminish your mileage by more than 10%. In the mid-range of torque where you drive your engine, it will take substantially more fuel to make it deliver the load. You will likely see it in your tachometer as well. Ethanol does burn slightly cleaner—in terms of pollutants— but as I said, the pollution has already been eliminated. When they’re talking about “cleaner”, that’s what they mean. Yes, I know Hot-rodders use alcohol fuels in dragsters, but that’s because they can radically increase compression without detonation. Fuel consumption doesn’t enter into their thinking at all since they’re only going a quarter of a mile.

The same people who fill your food with corn sugar and making you fat are now proposing to be your fuel supplier, driving up the price of food. Using food as a fuel is as environmentally irresponsible as you can be. If you REALLY care about the environment, REDUCE the amount of fuel you’re using. Saving energy through technology means reducing the waste side of the cycle—the exhaust, the traction, or the mechanical momentum. Gasoline engines are less than 30% efficient as it is, why make that worse by using watered down fuel? Work on the waste part of the cycle by re-using energy, such as using the engine as a brake in a manual transmission car (downshifting instead of braking), or by purchasing a hybrid, which uses the energy you accelerated with to slow you back down. Definitely buy turbocharged engines. Yes, they do use more fuel per cubic inch of displacement, but that’s because they produce more power, allowing you to buy a smaller engine in the first place. Don’t pump your accelerator, and your turbocharger will eventually bring your mileage back down.

In 2007, Transport Canada did a study on ethanol use and concluded that it actually causes higher emissions due to the higher consumption. We are NOT talking about pollution, by the way. CO2 is not a pollutant, but it IS a greenhouse gas. When we eliminated pollution from your emissions during the 1980’s—CO, SO2, NOX, something else had to replace those pollutants in the exhaust. An auto engine is an air pump that is literally sucking in tons of air to mix with a very small volume of gasoline (15 to 1 by volume, 350 to one by weight). Most of the air is nitrogen, so it doesn’t produce anything in the reaction. The oxygen combines with the carbon released when the hydrogen oxidizes and produces the power. You used to be able to commit suicide by locking yourself in the garage with the engine running, but that’s no longer true, because you’re engine is so clean burning (if it’s a newer that 1990 car and is not badly out of adjustment). So don’t bother. It will only add a headache to your other problems.

39

This pulse technique may increase gas milege a little. But just think, every time you do this you make the transmission shift up and down, lock and unlock the torque convertertor. Will all this extra abuse make the transmision clutches ware out faster? And in the end cost you big $$$ for major transmision repair.

You may be foolishly wasting your transmission minutes.

40

wolfeairwolfe, understand exactly the experiments you describe, but gotta tell ya… I don’t think the instantaneous mpg readout is helpful in this regard, it’s just too too sensitive to exact velocity and elevation change. Maybe if a car’s mpg readout gives a short-term average it would work better, but even then it’s hard to draw an accurate conclusion. And yes, I’ve done it on cruise, reaching the same conclusion.

My car has an ‘instantaneous’ gauge, plus other forms of mpg [L/100km, actually] functions built into the on-board computer that are used to calculate range which involve averaging the instantaneous data. Those functions can be accessed through the instrument cluster. I routinely monitor the fuel rate (L/100km) used to calculate range, which averages something like the last 20 miles… or 20 minutes, no way to tell precisely.

The measured rate is a very strong function of the stretch of road used, and even a slight grade can cause consumption to vary from ~ 10 L/100km to ~ 7.5 L/100km, over 30 miles stretches of the same road going opposite directions. I don’t have enough instrumentation regarding elevation change to be able to remove such a strong effect to make substantial conclusions.

Apparently the fuel around here must always have ethanol - or not, because I’ve never seen a 20% variation in average mpg over a tankful, on long trips where several tanks were used in quick succession. 20% covers the total mpg range I’ve measured in the last ~100k miles, including summer and winter: lowest ~ 23 mpg, highest ~ 28.

Aside from weight (just a driver vs. entire family), driving style and tire inflation seem to be the biggest contributors to average fuel economy. Just my $0.02 (USD). ; >)