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It'll help very marginally. If you really want to improve it, turn the engine off. Unless you're coming to a stop, keep in mind you have to regain any speed you lose effectively negating any gains from coasting. No it won't hurt the transmission. if you're worried about the transmission, give the car a little gas to get it up to the rpm it'll be at when you engage the trans again. Just make sure you get the fluid changed at the recommended interval. only certain manuafacturers and cars use off-throttle leaning out of the mixture. all are late models. |
Coasting in neutral works great in a standard-transmission car (or truck). Combined with moderate acceleration to an upper limit speed, coast till you reach a lower limit speed, then accelerate again... It's called Pulse and Glide.
With an auto tranny, you need to check your owner's manual to see if the car can be "flat towed" (section on getting towed). Depending on transmission design this may be safe within certain speed/distance limits. Many auto tranny's can't be flat towed at all. Confused?? From the auto transmission's viewpoint, coasting in neutral is the same as getting towed with all four wheels on the ground. Some trannys get insufficient lube to internal components in that situation. That's why you need to check your owner's manual. For standard trannys, don't coast with foot on the clutch. Bad for the throwout bearing. In neutral with foot off the clutch is the way. Some drivers kill the engine, some don't. |
Bruce,
my car manual says,"if the vehicle must be towed on the front wheels, don't go more than 55mph or farther than 500 miles or your transaxle will be damaged." when i EOC it's typically under 30mph and only 1/2 mile or less. sorry if this is a dumb question but, does it mean 500 miles lifetime or 500 miles consecutively? so, am i ok to continue?thanks. |
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Say you are idling at 60kph, at 700rpm. The force of friction on the engine (it will actually be a torque) will be x. Now say that you are coasting in 5th gear. In a typical small car, that might be 1500rpm. (In my car, it might be 2000rpm. But even here, a 660cc engine is a rarity.) So, the force (actually torque) of friction on the engine is going to be at least 1500/700 = 2.14x. Quite possibly, more. Few things are more efficient comparatively when moving fast. In the latter case, the car is going to be slowed down by the same forces of rolling and air resistance, + the torque required to rotate an engine at 1500rpm. In this case, you may be using less fuel instantaneously, but having to accelerate more at a later time. So although the engine may have the injectors turned off when feathered, you still may be losing more energy than the coast in idle. Feathered engine coasting is only going to get worse fuel economy the higher the speed at which you coast. Where using feathered or foot completely off, engine on coasting can be valuable is if there are unexpectedly stopped cars ahead. Since you have to slow down, the kinetic energy would be wasted anyway. |
Mighty Mira gave a good description.
Another way to see the same thing is, energy is needed to keep the engine spinning. Spinning twice as fast needs twice as much energy. That's completely aside from pushing the car! After having provided fuel to spin the engine, additional fuel is used/needed to push the car. But first you have to "pay" to spin the engine. So in almost all cases, the fewer total revolutions of the engine are used to complete your journey, the higher your fuel economy will be. Engine off at any given speed will give far greater FE than engine turning. Engine idling at any speed will probably/usually give better FE than engine engaged pushing the car. And, engine engaged in a higher gear will give better FE than engaged in a lower gear - as long as you're not lugging the engine, that is, rpm's so low that the engine runs poorly. My two cents. |
Thanks brucepick, I wasn't as confident as you about it (wasn't sure if pumping losses might change things), which is why I went the thought experiment route first. But the idea of "paying" to turn the engine was why I asked the question in the first place. Good explanation.
Another bonus of idling as opposed to having the car in gear (especially at high revs, like mine) is that the engine wear is reduced. Most of the wear occurs at the higher RPMs in other engines such as diesel generators, turbines etc. Just a few more RPM results in vastly reduced engine lifetimes. There must be a sweet spot speed for P&G, assuming engine on, neutral. Since idle fuel burn rate is static wrt speed, the faster you go the better from that perspective. That will work fine until a point, where rolling resistance and air resistance increase to the point where more energy is wasted in moving air etc. Note that there is also the pulse to consider. For that, we have to look at the engine map. Most of us probably have engines similar to the following engine map, which is a composite of EFI engines in 1995 (2 valve). In order to maximize efficiency during the pulse, we'd want to ensure that the engine was at least at 2000rpm and at about 3/4 of maximum load according to the graph (the line of the "island" represents equal efficiency (or Brake Specific Fuel Consumption, aka energy output versus, the each inner island having more efficiency than the next (read the link!). Hold on, I'll just compare: 2000 72% 3300 74% 3600-4500 70 - 100% https://img116.imageshack.us/img116/2...al27iy9.th.gif That's a lot higher than I thought. I was giving it 1/3-1/2 throttle, which I read somewhere on this site. I'll try and guesstimate what 75% of load is, since I'm not sure what the throttle required would be. Anyway, I'll have a think about it some more later. |
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I've successfully tried ram air induction in the air dam area. With a large enough intake area and tapered correctly, you can increase the volumetric efficiency and get several PSI boost at highway speeds. The drawback, of course, is sucking in dust, rain, rocks, bugs, garbage, etc. Add a grill to filter out the big stuff at least and get a K&N or equivalent filter because you will be cleaning it more often. I might try it on my current car since it is bone-stock right now and compare the results.
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(I copied the link address and opened in a separate window to see graph full screen.) And thanks to you, Mira! Can you give me more information so maybe I can understand the chart? Specifically, what is the meaning of the scale on the right (values shown .70-1.70)? And where do I/we see these in the graph: 2000 72% 3300 74% 3600-4500 70 - 100% Percent of what? Where is it shown in the graph? Any additional explanation would really help. I've seen these charts a few times and I just can't get the concept yet, even though I'm not tooooo bad in math. Thanks, Bruce |
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Sorry, the graph was actually in that link, but I'll post it here for everyone to see (immediately above). I also posted it in my spreadsheet for calculating pulse and glide, and regular steady state cruising fuel economy here. Anyway, you will see some dashed lines on that graph, 5%, 10%, 20%, 40%, 60%, 80%, 100%. That is % of maximum power. This is one of the easiest specs of a car to find. Notice that maximum power is only at 1 point in the graph, at about 5300 rpm. So if you have an engine map for your car, or something roughly similar, you can tell how much actual power your car is producing at that point in the engine map by multiplying the max power (hp or kW) by the % power at that point. So, to get 72%, 74%, etc, I was just interpolating values between islands. |
Many thanks, Mira.
I looked at the central isopleth a bit. What I see is of course first, the central point is right about 2000 rpm. And as you increase or decrease rpm from the center point you reach the isopleth ring pretty quickly. However as you increase/decrease load at 2000 rpm, you have a good distance to go before you reach the ring. Of course, it's just a graphic and changing the scale would change the shape of the central blob. But anyway you can make a case to not worry about load too much as long as it remains midrange, and try keep the rpms near the center point. In my case with an auto tranny without lockup, 2000 rpm is about the lowest I can run it when cruising over 50 mph before it downshifts. It's pretty happy at around 2100/2200 so I often run it there. I can keep it in or near the optimum range, but I have to pay attention. Thanks again! |
Overlooked the obvious
It's funny that I haven't seen one person put something up about trucks. I read this entire thread and signed up just to post this.
2-3 MPG - put tailgate down. 3-5 MPG - remove tailgate. 1-3 MPG - put in one of those aero nets. I've noticed several people talk about indexing plugs, but I've had terrific luck with Bosch +4 plugs. Amsoil. I swear by the stuff. If your rig has the room, definitely get the externally mounted double oil filter. 1998 Nissan Frontier, 182K miles, 2.4L DOHC engine, 5-speed manual. Amsoil since I bought it, Bosch +4s, had tailgate up less than 25x in six years (2001-2007). Nearly new when I bought it. I averaged 32 MPG. Highway, actual real-world miles - 36 MPG, about 120K of those miles. Wouldn't drive it over 60, and it could tow a 12-foot U-Haul trailer 1800 miles, both springs on truck and trailer bottomed out, never went below 40 MPH and 3rd gear. All this with a 3025 pound curb weight. Turned A/C off or removed it from belt system (different belt, A/C hooked to other items) for best mileage. I MISS that truck. Stock was 22/26. Revised EPA estimates 20 city/24 hwy. Yes, I really could get 36 MPG out of that thing without the tailgate, Amsoil and +4 plugs. I did the same trips repeatedly (Seattle to Los Angeles and back, about once per month for three years) and found the +4s gave me about 3-4 MPG, same with Amsoil, same with the tailgate. Exact same stops, same gas stations, same time of day (better MPG in daytime), etc. Thought you'd like to hear that one. BTW tailgate UP for snow and better traction. |
Overlooked the obvious
Edit: removed double post
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well that depends on the size and configuration of said truck. lets say a regular cab regular bed s-10 compared to a full size quad cab regbed dodge ram or somehting.
not to mention all the different cabs: quad, extended, regular then beds, short, long, regular, fleetside flareside then full size or compact pickups. then all the different brands, some with smooth curved fronts, others flat boxy fronts. so what works with one might not with others ya know? just like cars... |
...i think he forgot to say his tailgate was about 12' tall
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Don't drive if you can walk. It's not only good on gas, but it's better on your waistline.
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Hello, very nice forum here. My very first post.
I was wondering if changing to manual transmission should be on the list. Manual transmission is always lighter (at least in the cars I know). I have always thought about manual transmission as more fuel efficient in general, though I have never seen any real studies. |
maybe but LOTS easier to coast with manual, will last forever, can upshift downshift and prepar for upcommin road events, engine brake quicker and more while going downhills (maybe not a BIG advantage gas wise cuz an auto can do the same but maybe save on brakepads etc) dont have to do 30k fluid changes just every 100K swap fluid so you may save on not having to buy filter+gasket+fluid every 30K or so.
plus even if you have a slow car it can seem fast and fun with a manual tranny. |
Thanks for all the tips. I'm very interested in any cheap way to increase mileage.
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just want to make clear, this was Brucepick's idea. i believe more gas is getting/staying in my tank. hey! and why not try it? it's a cheap/free mod/experiment! |
I read recently that you should not inflate the tires to the maximum on the tire walls, but rather there is a sticker in the inside of the door that has recommended tire pressure and it's different for each make/model of car, and that's the number you should go buy.
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It depends on what your goals are. If you want better FE, then you crank up the pressure. It will have an effect on ride and handling though, so it takes a little getting used to.
Lower pressures generally mean more tire wear, wasted fuel, and increased risk of blowouts on the other hand. Do I get a royalty for telling you this? ;) |
LOL, thanks for the reply. That is most helpful. Feel free to signup on my website for a list of 34 ways to save gas money, perhaps a few ideas that aren't on this list.
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Not sure if this has been mentioned but NEVER try to beat a light!
It can be so hard to resist, to give it just a little extra gas in hopes that it won't turn red just yet, but what happens is this: - The chances are about 50-50 regardless, no matter what you do that light will either stay green, or turn red. For real, I used to think if I went a little faster that this would improve my chances, but honestly speaking I doubt very much it does anything at all. If you try and beat it and it turns red, that just wasted a TON of fuel. Not to mention extra wear and tear on the brakes and tires. And no, the few times you do beat it don't compensate for it, it doesn't even add out, it is a losing proposition every single time. This is speaking from personal experience, best thing to do is keep a steady speed, maybe even slow down a little before the big bad intersection. Quote:
Please remember, if you hit someone in the rear it is YOUR fault! The reason it frustrates is because a not-at-fault accident still wastes my time. |
And another thing about tires...
Don't be in such a hurry to buy brand new tires when the ones you are riding on have even wear. I took a 5 mpg hit (from 44 to 39 mpg) when I replaced my well-worn front tires with Blizzaks. Of course I did it for the winter conditions (the Blizzaks sure are sticky), which is also affecting my FE to be sure. For research on tire rolling resistance, check out this study from the National Academy of Sciences:
https://www.nap.edu/catalog.php?record_id=11620 Regards, Bill |
freshly green
first thread ever... so bear with me please.
1. does premium gas make any difference in FE? 2. how does the grille blocking actually work? 3. what is an ideal coasting speed in the city? thanks all:) |
Welcome! You should make a post in the Introduce yourself forum.
Premium typically negatively affects most modern vehicles, or has zero effect. Premium *mostly* has additional additives to prevent knocking rather than increased energy. Ideal coasting speed is the speed limit, sustained for as long as you can actually keep it up. Too many factors otherwise. Use the search tool to find some excellent threads on grill blocks. The basics are that air is diverted around the vehicle because it's not flowing through holes in the front. The fine-tuning is the art. |
Since getting Tracer and Escort Wagons, and becoming mpg conscious... the following changes have been worthwhile:
Drive gently. I never floor it, I try to anticipate slowdowns ahead, accelerate gently. Related - if I see a light changing or gone stale ahead, I coast. Shutoff motor at stops. If it is a short one, don't bother; but if I'm approaching light and it turns red, I"ll often shutoff motor, coast to stop... and fire it back up again right as light turns green. Works. fine. Tire pressure - crank it up to about 40psi. Now the Wagon gets 40mpg. Remember this: whenever you step on throttle or brakes, it costs money - minimize both! https://www.fuelly.com/attachments/fo...8d1b964d91.jpg |
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I would say 20% is in the maintenance, another 20% in the driving.
More so if nothing ever gets done, and one has never experienced driving with an FE gauge. And it takes time, but I dare say one can improve a vehicle's mpg by UP to 40% (thou 10-20% is more like it, especially at first, the later parts can take years). Definitely slow nice and easy driving. Even ONE heavy footed acceleration per tank hurts mpg by at least 0.1, doesn't even have to be to the floor. Letting off the gas way earlier by anticipating possible stops, and coasting off speed versus braking, Exit ramps on the freeway are great for practicing this (I almost never have to touch the brakes on these anymore, and safely so). Another one is if the light turns green but the one ahead just turned yellow, might as well just mosey up on it. Some folks believe drafting helps, but I disagree: ONE tap of the brake pedal and it's over, I find the constant speed adjustments I have to do in these situations hurt mpg as much as the draft helped (plus I HATE tailgaters and it is dangerous). I find keeping a 6-8 second distance from the car in front far more beneficial, I can just let off the gas when they already have to stop, and keep a more constant speed, to me this outweighs all the drafting garbage. Quote:
Mine doesn't even have traffic, just from it telling me where to turn instead of me doing it. Found more than one road I never knew existed. |
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you could possibly get a ticket in Virginia for 'drafting'(tailgating). we consider it 'aggressive driving'. Besides who's ever seen a semi going the speed limit?
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Get Better Gas Mileage
Here is a page that I wrote which goes into detail about some of the best tips for saving gas and increasing the gas mileage of your car: Tips for Getting Better Gas Mileage. Most of these suggestions are relatively easy and don't require a complete change of your lifestyle or driving habits.
As the prices of gas continues to climb, this topic is going to become more and more important! |
Here's a driving technique: Drive off center. Most places have roads that are worn, and have grooves. The further you stay out of the grooves, the smoother the surface is. You can tell instantly by the sound difference. I don't know how this translates to FE, but it's too easy not to pass up. I have my car lightened to the point of no (heavy) sound deadening, and smooth roads make a huge diference. Also, in the rain, I'm less likely to hydroplane on my overinflated tires, because those grooves hold the water.
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re:save gas
Walk?
Well you did say to save on gas, not save on saving gas in a "car" HAHA- just kidding :p My husband and I are saving on gas "in our cars", if anyone's interested- see signature link. I will also provide additional endorsement links if you PM me :) ...something that's working for us, so I wanted to share.... Quote:
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not sure if someone said this already, but fuel injector cleaner helps out alot. i drove a 92 toyota mr2 and that stuff works very well. it's about three dollars fr two bottles but each bottle gives me an additional 40 miles to the tank! but this only works if you use the cleaner with shell gasoline but a very inexpensive method to save alot of gas. Also, the older your car is, the better it works!
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Last trip in my VX was mostly interstate in Virginia. I stayed in the right lane and followed the trucks about 100-125 feet behind them which is close to the distance I could stop completely. 65.744 MPG for 304 miles. The trucks have slowed down here to conserve fuel, and on 95 the idiot drivers will not cut in front of you or do other stupid things when you are in the right lane behind a truck. Some of the trucks in Va are now tandems which have a trailer hitch for the second trailer. They have a steel panel that goes down between the tires to just a few inches off the ground which seems to help with airflow under the truck. Average truck speeds now are 67 MPH, not all of them but the majority. Find a truck driver that anticipates traffic flow in front of him and use downshifting instead of brakes to take advantage of fuel shutoff when your foot is off the gas. This trip I was carrying about 600 total pounds of passengers and cargo. Va state troopers will not even think about giving you a ticket for that following distance, and you have a chance to react and avoid road debris. Coast on long downhill sections.
regards Gary |
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Drafting works very well. at least if you draft a semi. Especially if you are driving long distances. Had an s-10 pickup that got a max of 24 mpg and drafted a bus on a long trip once and got over 30. But yes your right, it's dangerous. |
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