Driving for better mpg

[shizzler]

Nice logic there wksg. I follow and concur! I've always wanted to use calculations of expected vehicle acceleration and deceleration, and lay them atop the plot above, then integrate the chart for an expected mpg. Too lazy though, haha.

 

[gdr703-2]

It seems likely that the pulse time would be shorter than the glide time. Let's say the time is split 40/60 pulse/glide, instead of the 50/50 above. Working through the same gyrations, I'd calculate now 65.6 mpg.

Yes, I agree that's better.
Also you are right it wont be a 50:50 split, basically because in the constant cruise the assumption is 17Kw generated, and yet in the pulse the engine is making 40kW, actually I'd figure more like 46kW, so therefore making 2.7 times energy in the pulse. So the split would be more like 40% pulse and 60% glide, er mebbe, as you suggest.
Anyway Its clear that pulse and glide does work.

cheers, Richard

 

[Wksg]

The split might be even more favorable. Today I P&G'd for most of my 120 mile commute:

Pulse: 65 mph to 80 mph about 8 seconds (not quite full power. about 2200 to 2800 RPM)
Glide: 80 mph to 65 mph about 16 seconds

So the split is about 30/70 pulse/glide. That was a rough timing. Probably 40/60 is a realistic estimate.

It seems like I ran about two pulse/glide cycles per mile. A little more, the third pulse started just before the next mile. Thinking about it now, that has to be about right, since two cycles takes 48 seconds per my estimate above, which is an average of over 70 mph.

I don't find it very difficult to do this. Kind of fun, actually. I just push in the clutch while gliding. Is there any difference between this and putting it in neutral? I wouldn't think so.

shizzler's aero mods would be great for this, they would extend the glide time.

In the end, I would think that this pulsing at high torque, and extra pushing on the clutch pedal, will increase wear and one would have to balance the costs of that vs increased fuel economy. On the highway, anyway. In town, I can see where it wouldn't matter much, it would be easy to do P & G.

 

[Wksg]

I took a video of my version of pulsing and gliding today:
http://www.youtube.com/watch?v=a3vGliIbnMU

Four cycles, and averaging the times, I get 8.2 seconds pulse, 15.9 seconds glide, for about a 35/65 split. This was a flat section of US23, not sure which way the wind was blowing though. Not full power during the pulse, but close. Doing this probably keep the turbo and intake manifold clean!

So this should give an improvement in fuel economy, we'll see. It's cold and lousy weather, I still find it amazing that anyone can get over 50 mpg on winter fuel and with this crappy weather.

Oh, and please let me know if my P&G technique could be better!

 

[gdr703-2]

Kind of fun,
there any difference between this and putting it in neutral?

shizzler's aero mods would be great for this, they would extend the glide time.

I would think that this pulsing at high torque, and extra pushing on the clutch pedal,

Yes adds a new dimension to your daily commute, as to figure how best to pulse, and where will the glide take you to.

Push in the clutch or engage nuetral, i do the latter. also means you arent spinning gears which probably uses a tad of energy.

I'll have to look up the aero mods.
Mine have been to block off the hole not occupied by the fan behind the radiator, and move the weight forward to encourage nose down tail up attitude.

The clutch - is there an issue? well mine is the original and going strong after 9 years and 270,000 km. as is the battery etc etc.

cheers, Richard

 

[Dave_D]

Have you considered the impact of going into neutral in this? If you are gliding with the foot off the pedal in gear then no fuel in injected, but obviously there will be some engine braking. If you glide in neutral you glide longer, but then you need to inject fuel to maintain the idle. Of course the glide time will also be a function of the speed, as aerodynamic resistance goes up with the square of the speed.

Dave

 

[Wksg]

Have you considered the impact of going into neutral in this? If you are gliding with the foot off the pedal in gear then no fuel in injected, but obviously there will be some engine braking. If you glide in neutral you glide longer, but then you need to inject fuel to maintain the idle. Of course the glide time will also be a function of the speed, as aerodynamic resistance goes up with the square of the speed.

Yes, qualitatively anyway. I don't have any proof, but I think that gliding in gear would give poorer results. Yes, you save a few liters over a tank, but you spend more time pulsing, since your glide time is reduced. So you use more fuel pulsing, and I think you'd end up using more than you save from not idling.

I could be wrong!

 

[Wksg]

I used the pulse and glide during cruise on my mostly flat daily commute for most of the last tank. In the end, it did not make a big difference: 741 miles on 15.3 gallons, 48.5 mpg. That's within 1 mpg or so of what I've recently been getting.

Having said that, it has been quite cold here in Michigan recently. My very best tank has been only about 1 mpg higher, and that was when it was warmer, and on average I was probably going slower.

No breakthrough yet!

 

[shizzler]

Gliding in gear, at zero throttle would probably be worst. There is significant engine friction at highway cruising speed engine rpm (especially with stock 5th gear). To simply let that friction rob your vehicle of kinetic energy seems wasteful. Yes, the engine is using zero fuel, but you are quickly transferring vehicle energy purely into heat (and wear!).

So then I see two modes of P & G. Coast down in neutral (un-throttled idling on a small diesel engine uses a very tiny amount of fuel). Probably the most efficient, but a lot more wear and tear on the clutch. Also, it can be inefficient to spool the engine back up and re-engage the gear (akin to the common puff of smoke on throttle tip in). An experienced hyper-miler would probably get very good (read= smooth) at this though.

Or, coast down in gear but with light (~5-10% ??) throttle. This can extend the coasting phase dramatically. Basically you use enough fuel to overcome internal engine friction and coast down just from aerodynamic drag and rolling resistance losses (or even fight them a little with some fuel input). Benefits to this technique include less wear on the clutch and smoother transitions from P to G and vice versa. And longer coasting periods that you can tailor to fit the road conditions (traffic, hills, stop lights, etc).

Not sure what is best though.

 

[gdr703-2]

Or, coast down in gear but with light (~5-10% ??) throttle. This can extend the coasting phase dramatically. Basically you use enough fuel to overcome internal engine friction and coast down just from aerodynamic drag and rolling resistance losses (or even fight them a little with some fuel input). Benefits to this technique include less wear on the clutch and smoother transitions from P to G and vice versa. And longer coasting periods that you can tailor to fit the road conditions (traffic, hills, stop lights, etc).

Not sure what is best though.

Sorry but I cannot agree with that for the following reasons:
With a light throttle you are buring fuel very inefficiently, like at 500, instead of in the pulse at 210.
Forget about wear and ttear on the clutch. Mine is the original, and fully operational after 270,00 km.
Also by coasting in gear you are still turing the engine over at 2500 rpm, which requires either fuel or consumes energy out of the vehicle at the rate equivalent to (say) 1.1. What you need to do is to get the engine rpm down to 900, and the equivalent fuel requirement to keep that engine turning over is 0.4

Its clear what is best.
Try it for your self, and I suugest iver three tank fulls, and appreciaqte that this is a technique that is most likely alien to your fundamental thoughts about the way you were introduced to drive, and it will take you some time to acquire the skill.
But its worth it. Fun and good MPG's

 

[shizzler]

What do you not agree with exactly? I stated that neutral coasting was probably more efficient and then only listed attributes of both techniques... You didn't really refute my post.

Of course that the fuel conversion efficiency (BSFC) is bad at light throttle, but that effect is negated by how little power you are requesting. So its high specific consumption, but multiplied by a tiny amount of power. So the net fuel consumption is still very low. Combine this with a much longer coasting period and its not so bad.

If your numbers are correct that maintaining neutral rpm uses fuel at 0.4 / 1.1 the rate of cruising rpm, then you'd only need to coast for 3x the distance/time in gear to achieve similar overall efficiency, right? Seems plausible.

I still don't disagree with what you say about neutral coasting being more efficient overall though.

I have tried both methods, closely watching my scan gauge. But I will never have the patience (or clear traffic) to sustain this for a full tank. That's why I aero-modded my car... high speed cruising without the penalty in mpg.

 

[Wksg]

Try it for your self, and I suugest iver three tank fulls, and appreciaqte that this is a technique that is most likely alien to your fundamental thoughts about the way you were introduced to drive, and it will take you some time to acquire the skill.
But its worth it. Fun and good MPG's

It would be great if you, or someone with your skills at doing this, could post a video .... P&G for Dummies. Then I might be able to get it. Mostly, I'm interested in flat terrain.

I should get a scangauge. It is hard to go by "feel" and who knows what my engine is like compared to yours or others. Do I use 500 g/kWh at light throttle? Am I in the 210 g/kWh range when I'm pulsing? Dunno.

Remember too, average speed counts, even (especially?) when using pulse and glide. I'm sure I could do a lot better doing P&G between say, 55 and 70 mph, but I can't average 62 mph on my commute and maintain sanity.

Speaking of sanity, the mood grabbed me today and I did a couple of 80 to 100 mph P & G cycles. What a blast !!

 

[rotarykid]

In my experience most of the time coasting in "N" uses the least amount of fuel in a gasser or diesel compared to just staying in gear on lower speed city loops & on rolling terrain . That is when no acceleration is required on a slight or more grade down and when you're up to the fastest speed required before a stop may be required coming up .

A perfect example of this is on streets that I drive on daily . When I leave the house there are 3 lengths of road that are ~1 mile long slight down grades after a stop light on a 30 mph posted section to connect to the highway . A slight pulse up to say 23-25 mph allows you to glide up to 30 mph before you reach the bottom of each hill . Then a slight pulse up the hill then back to "N" to coast to the bottom of the next hill . Repeat as conditions allow ...........Coming back home there are also stretches that fit the above descriptions .

Over ~17 years in 9 different cars/vehicles , 6 diesels & 3 gassers I've clocked a consistent 3-5 mpg increase over a tank when the above described is used on this stretch .

I also always shift into "N" when ever I've reached my desired speed on a stretch of road when I know a stop may be required at some point coming up . If it turns out that I don't need to stop it's back into gear to continue down the road . And on the open road @ speed when ever there is a down grade steep enough to hold speed I shift into "N" then back into gear when the hill starts to flatten out . And I always shift into "N" when coming to a stop and when stopped in anything automatic to reduce load & trans wear saving fuel .

Over the last 33 years I've used this technique whenever possible over a tank to clock as much as a 10 -~13 mpg increase over that tank in various vehicles . Those vehicles include VW , Audi , Mazda , Nissan , Volvo , Buick , Chevy , Ford & Toyota gassers & diesels , Daewoo , Kia , Honda , Porsche & Mitsubishi gasser vehicles . I also have clocked close to a 15 mpg increase in automatic gassers while doing this in Audi , Daewoo , Kia , Honda , Mitsubishi & Toyota vehicles over just staying in "D" in varied driving conditions .

Over that 33 years of driving I've calculated consumption on almost every tank over 3,000,000+ miles traveled if I had the data to do so . I never just fill and go anything if I have the data . And I always fill to the brim if I have filled the car to get accurate fill data , the only way I know to really get an accurate idea of consumption .

To me calculating consumption is a big part of the fun of driving , that is seeing what a given vehicle can actually produce consumption wise when effort is used . And I always do this over many tanks to get a real picture of a given vehicle's consumption rate .

 

[rotarykid]

It would be great if you, or someone with your skills at doing this, could post a video .... P&G for Dummies. Then I might be able to get it. Mostly, I'm interested in flat terrain.

I should get a scangauge. It is hard to go by "feel" and who knows what my engine is like compared to yours or others. Do I use 500 g/kWh at light throttle? Am I in the 210 g/kWh range when I'm pulsing? Dunno.

Remember too, average speed counts, even (especially?) when using pulse and glide. I'm sure I could do a lot better doing P&G between say, 55 and 70 mph, but I can't average 62 mph on my commute and maintain sanity.

Speaking of sanity, the mood grabbed me today and I did a couple of 80 to 100 mph P & G cycles. What a blast !!

In my experience on flat terrain not much other than a light foot when accelerating , paying very close attention to traffic conditions to use the brakes as little as possible , using "N" on city lower speed city loops whenever conditions allow and killing the engine on long glides when the engine is cold will improve mpgs . And killing the engine while rolling is the last thing I would ever suggest on anything automatic . On truly flat terrain anything you try is going to have little effect on consumption especially on the highway .

Hills , grades or something , anything where gravity can help you travel without power on a length of road are required to use most of things/techniques that actually work to reduce consumption .

In fact to save fuel all the techniques I know that work use gravity , a grade to make them work on highway runs . To save fuel when you coast any length you're using gravity to produce power to keep you rolling to save fuel from needing to be burned . In my experience pulse & glide only works if you have a down grade to help hold speed or if you don't have to speed back up after the energy was spent to get up to speed . This technique only works on flat terrain to save fuel if you know a stop light/sign is coming up and you can produce enough speed to keep rolling until you reach that stop after you disengage the trans .

 

[Wksg]

Thanks for the feedback. I can see where city driving can respond best to technique. My commute, though, is 60 miles one way, pretty darn flat, highway miles with no reason to slow down.

I think the P&G technique actually does help on the highway, but you probably have to get it just right.

 

[Turbospool]

In my experience on flat terrain not much other than a light foot when accelerating , paying very close attention to traffic conditions to use the brakes as little as possible , using "N" on city lower speed city loops whenever conditions allow and killing the engine on long glides when the engine is cold will improve mpgs . And killing the engine while rolling is the last thing I would ever suggest on anything automatic . On truly flat terrain anything you try is going to have little effect on consumption especially on the highway .

Hills , grades or something , anything where gravity can help you travel without power on a length of road are required to use most of things/techniques that actually work to reduce consumption .

In fact to save fuel all the techniques I know that work use gravity , a grade to make them work on highway runs . To save fuel when you coast any length you're using gravity to produce power to keep you rolling to save fuel from needing to be burned . In my experience pulse & glide only works if you have a down grade to help hold speed or if you don't have to speed back up after the energy was spent to get up to speed . This technique only works on flat terrain to save fuel if you know a stop light/sign is coming up and you can produce enough speed to keep rolling until you reach that stop after you disengage the trans .

Yup ...... Rotary has it right , you need moderate hills to make this work best. I second the experience above. I have a 25 mile commute to work every day (50k daily)and average 53 in cold weather 63 in warm with P&G fun.

 

[robbieyukon]

I checked my tires tonight to see what the factory psi was. There were all between 35-39psi each. I filled them all up to 45psi which is 90% of the tire max psi. Still rode well driving home.

 

[gdr703-2]

I have a couple of questions for you guys and dolls.
Given that my Golf TDI, after 9 years and 4 months, covered 276,728 km, at 4.02 L/100 [59mpUSg] what might my new car attain? (The commute remains the same)
And what is my new car? (it’s a hatchback)
The differences are:
It has more ground clearance, and is less high, a tad wider, a chunk longer.
Its heavier, by 12%
The tires are wider, 205 vs 195, so more fuel required. They are Bridgestone Potenza, vs Michelin Energy, or Nokian WRG2
The engine revs higher, 60mph is more like 2,600 rpm, which will use more fuel to keep it turning, but will show good improvement in a glide.
It has All wheel drive, which will use more fuel.
It cost a whack less than a replacement Golf TDI, enough to pay for many years of fuel.
It’s a gasser.
Gas has maybe 8% less energy than Diesel.
It doesn’t have a fuel return pipe, so the Pulse part of pulse and glide will need to be handled carefully.

Its published highway consumption is 7.4 L/100 [32mpUSg] - the golf was 4.9 L/100 [48mpUSg]
GDR703 rides on, it has assumed a new moniker, and a fresh pilot.
cheers to one and all. . . . . .

 

[740GLE]

you get a subie?

 

[UFO]

I have a couple of questions for you guys and dolls.
Given that my Golf TDI, after 9 years and 4 months, covered 276,728 km, at 4.02 L/100 [59mpUSg] what might my new car attain? (The commute remains the same)
And what is my new car? (it’s a hatchback)
The differences are:
It has more ground clearance, and is less high, a tad wider, a chunk longer.
Its heavier, by 12%
The tires are wider, 205 vs 195, so more fuel required. They are Bridgestone Potenza, vs Michelin Energy, or Nokian WRG2
The engine revs higher, 60mph is more like 2,600 rpm, which will use more fuel to keep it turning, but will show good improvement in a glide.
It has All wheel drive, which will use more fuel.
It cost a whack less than a replacement Golf TDI, enough to pay for many years of fuel.
It’s a gasser.
Gas has maybe 8% less energy than Diesel.
It doesn’t have a fuel return pipe, so the Pulse part of pulse and glide will need to be handled carefully.

Its published highway consumption is 7.4 L/100 [32mpUSg] - the golf was 4.9 L/100 [48mpUSg]
GDR703 rides on, it has assumed a new moniker, and a fresh pilot.
cheers to one and all. . . . . .

It might attain 25mpg. 30mpg with aero mods and skillful driving.

 

[nicklockard]

You got a WRX. I agree with UFO. It's going to be thirsty. You'll be lucky to average 24 mpg in the real world.

 

[gdr703-2]

you get a subie?

Well done, you are certainly smarter than I.
In 2002 When I bought the Golf TDI the also ran was the Subaru, but it was 16% more expensive. Today the situation is reversed, the Golf is 28% more expensive than the Subaru.
That’s quite a switch around in the Value Equation !
Not sure whats underlying it, foreign exchange rates maybe, or market perceptions? Anyways I don’t figure in the VW target market these days.
Anyhoo, the Subaru is really tight, doesn’t want to glide, although it is showing signs of loosening up. And the pilot has to figure out the best Pulse mechanism, as its not as clear cut as it is with the TDI. Looks like the mileage will end up some place in the low 40’s mpUSg, as Its tinkering around 36 at the moment.
Cheers, Richard

 

[gdr703-2]

I agree that this car would make 25mpUSg if my commute were 10 miles. However my commute is 30 miles, and therefore I am currently running at 38mpUSg, and expect to do better as I get a few things worked out.
What this points to is the cold start penalty, which requires particular attention, as it has a very significant influence on the overall mpg. That is to say the first 5 minutes (3 miles) in the morning can be driven in a number of ways, and as this engine is overfuelling when cold, its quite easy to get it wrong, and not just a little wrong either. Its becoming apparent that I need to develop a particular technique for the first 5 minutes. The engine needs to be allowed to get to operating temperature before being given any significant rpm/load, else the overfuelling situation becomes extreme.
cheers, Richard

 

[Fordcougar]

Best tip for me is let my wife drive... last tank was primarily her driving
38mpg(our best tank)
Of course if I stay on our rural roads(45-50mph) I can manage 44mpg
forget it on the highway 70mph yields 37 roughly

 

[ezshift5]

I am really impressed with the EA211 1.4L turbo in my '17 VW Jetta (S)..........

1. No issues at all since new Summer/Fall 2017. 53.9 MPG per Fuelly.Com Fall 2022 - Round trip (50th HS reunion (Wife's) circa 900 miles - mostly onI-5

 

[14BeetleCJAA]

I am really impressed with the EA211 1.4L turbo in my '17 VW Jetta (S)..........

1. No issues at all since new Summer/Fall 2017. 53.9 MPG per Fuelly.Com Fall 2022 - Round trip (50th HS reunion (Wife's) circa 900 miles - mostly onI-5

That’s not a TDI though . But yes, I had a 2024 Jetta on loaner from the dealership; same engine, and I was equally impressed. I’m a “drive it like you stole it” guy, and still averaged 35mpg over 1200 miles worth of driving.

 

[Fix_Until_Broke]

Co-worker had a 1.4TSI 6 speed manual Jetta and claimed it got the same MPG as his 03 ALH 5 speed (low 50's). He drove a lot of miles to/from work every day so had reliable numbers and hundreds of tanks to substantiate the claim.

 

[turbobrick240]

That’s not a TDI though . But yes, I had a 2024 Jetta on loaner from the dealership; same engine, and I was equally impressed. I’m a “drive it like you stole it” guy, and still averaged 35mpg over 1200 miles worth of driving.

Not the same engine- that '24 loaner had a 1.5L engine.

 

[14BeetleCJAA]

Not the same engine- that '24 loaner had a 1.5L engine.

Either way, the new Jettas are very fuel efficient gassers. With prudent driving practices I could have easily achieved a 45-48mpg avg.

 

[privateTDIjet]

Time will tell for their reliability.