Fuel saving thread

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  • #1
wolram
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Main Question or Discussion Point

Motoring.

With fuel prices so high it seems a good idea to try every way we can to save fuel,
Are there any TESTED methods that save fuel, any gizmos that actually work?

Take for granted that your vehicle is in top running order, engine tuned, brakes running free,
tyres at correct pressure etc.
 

Answers and Replies

  • #2
FredGarvin
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In my travels I have not seen any product that has been proven to help increase gas mileage. All of the things you listed plus altering driving habits, i.e. drive slower and less frequently, are the only things I know of proven to help. I have had a couple of co workers try upgraded engine control chips. They were busts (which I completely expected).
 
  • #3
Danger
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The part about the engine being in top running order implies that most of the 'little' fixes are already in place. That includes stuff like top-notch ignition pieces and tuned fuel delivery.
Removing extraneous power-hogs like A/C compressors can make a big difference as well.
 
  • #4
wolram
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One tip i found.

A roof rack or carrier provides additional cargo space and may allow you to meet your needs with a smaller car. However, a loaded roof rack can decrease your fuel economy by 5 percent. Reduce aerodynamic drag and improve your fuel economy by placing items inside the trunk whenever possible.

Avoid carrying unneeded items, especially heavy ones. An extra 100 lbs in the trunk reduces a typical car's fuel economy by 1-2 percent.

So clear the junk from the trunk.
 
  • #5
wolram
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Removing extraneous power-hogs like A/C compressors can make a big difference as well.
Would it be safe to just take the drive belt off?
 
  • #6
FredGarvin
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One thing I know does help is to use cruise control whenever possible on trips. I experimented with my truck on trips. It does indeed help.
 
  • #7
NoTime
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Would it be safe to just take the drive belt off?
If the belt is not driving anything else and you don't mind the early demise of your AC compressor then yea it's safe, barring any injuries you might cause to yourself mucking about in the machinery.
But, when you are not using the AC then the clutch is off and the power to run the belt is minimal. Note that many cars engage the AC for a few seconds now and then to keep the compressor seals from drying out.
 
  • #8
Mech_Engineer
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One tip i found.

A roof rack or carrier provides additional cargo space and may allow you to meet your needs with a smaller car. However, a loaded roof rack can decrease your fuel economy by 5 percent. Reduce aerodynamic drag and improve your fuel economy by placing items inside the trunk whenever possible.

Avoid carrying unneeded items, especially heavy ones. An extra 100 lbs in the trunk reduces a typical car's fuel economy by 1-2 percent.

So clear the junk from the trunk.

I have had my loaded roof rack reduce my fuel economy by as much as 25%, depending on what it was and its aerodynamic shape.

And carrying a lot of extra weight is a big thing many people tend to overlook. in a 3000lb car, just 100 lbs is a 3% increase, which should in theory reduce your city mileage by about 3%. I've seen some people carrying 500lbs of random stuff and wonder why their city mileage sucks.

As for tricks that increase mileage, I would say properly inflated tires that are lightweight and the proper diameter for your vehicle is a big one (lightweight wheels help too, magnesium or aluminum alloy). Reducing weight and reducing rotating mass goes a long way towards helping city mileage, as well as of course being light on the accelerator. Accelerating quickly (and braking quickly and/or often) are huge drains on in-city fuel economy. In-city economy is all about retaining as much kinetic energy as possible at all times, because braking is energy you can't get back without a hybrid system. Each time you stop, you have to burn fuel to regain that energy your brakes scrubbed off.

For peak mileage on the highway, your engine should be at the rpms where its peak torque occurs for your goal highway speed. There is of course a measurable difference in mileage between 60 and 65mph, and 60-75mph is a big difference, so the slower you go the better (within reason, in my experience most cars get peak mileage at 55-60mph). Keeping the vehicle as aerodynamic as possible helps too, so removing extraneous items like cargo racks can help. Also making sure your car has properly placed aerodynamic diffusers front and rear can make a tremendous difference, as well as underbody aerodynamics and ride height.
 
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  • #9
symbolipoint
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This concept seems nice although uncertain how close it comes to achievable reality:

Buy your fuel at the coldest time of the day (or night). Materials like liquids will be more dense when cold and so each gallon gives you more mass when cold than when warm.
 
  • #10
Mech_Engineer
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This concept seems nice although uncertain how close it comes to achievable reality:

Buy your fuel at the coldest time of the day (or night). Materials like liquids will be more dense when cold and so each gallon gives you more mass when cold than when warm.
Unfortunately, this wouldn't work because the fuel is stored in underground tanks that are pretty much constant temperture from day to day. Fuel store managers do have to worry about this though, because when a truck delivers gas its tank is at ambient temperature, but the underground tank is usually quite a bit cooler and so they end up paying for more gas than they get due to thermal expansion.
 
  • #11
turbo
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When I was performance-tuning my venerable old Wide Glide, I was looking for horsepower more than anything. Since I was running an S&S Super E racing carb, performance was a bit doggy at low speeds. The Super E is a butterfly carb and when the throttle plate is partially closed, it reduces the air-flow over the main-jet venturi which impedes proper atomization. I installed a Yost power tube (pre-atomizer) in the venturi, and was able to increase the main jet size without over-rich performance, and got an immediate, large improvement in throttle response. Best of all on weekend runs with my wife on the back, I went from 45 mpg to 50 mpg. That's about the only time I could ever measure my mileage accurately, because if I was riding solo, I'd be on the throttle a lot. If you are running a carburetted vehicle and if Yost makes a Power Tube for that application, I highly recommend installing it. The more finely divided the fuel is, and the better it can mix with intake air, the better the performance AND the better the fuel economy.
 
  • #12
wolram
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Would fitting an electric fan instead of the engine driven one improve millage?

And air filters do the trick ones work better?
 
  • #13
wolram
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Change to performance exhaust system?

Cut the use of day time lights.

Manufacturers fit the cheapest possible exhaust system, some performance exhausts claim 10 to 15 % better fuel economy through better exhaust flow and better cylinder scavenging.

Running with lights on in day time increases alternator loading and thus power sapped from engine.
 
  • #14
turbo
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I tend to use K&N air filters. Wash them, dry them, oil lightly and reinstall. The seem to flow more freely than stock Harley filters, since I could re-jet slightly larger after switching without over-rich operation.
 
  • #15
mgb_phys
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Cut the use of day time lights.
They are typically only 5W bulbs - so you are saving 10W from your 60HP/50Kw engine load.
 
  • #16
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The only REAL way to save on fuel is to not drive. ;)

The other method (besides the maintenance ideas all ready mentioned) that can save a small fraction, is to drive courteously. Aggressive driving uses more gas. Sitting at traffic lights and in traffic jams are also gas guzzlers.

Drive wisely!
 
  • #17
wolram
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They are typically only 5W bulbs - so you are saving 10W from your 60HP/50Kw engine load.
You would be amazed by how many people in the UK drive with head lights on, some even have extra spot lights on in perfect visibility.
 
  • #18
mgb_phys
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Side lights are compulsory over here.
Strangley my car turns them off when you put the handbrake on - even if the engine is running. It's a manual and I learnt in the UK so I put the brake on like a good little safe driver everytime I stop.

Having a manual here is a great anti-theft device - people steal your car and drive off in first gear. It also means you don't have all that safety interlock crap where you can only start of the seatbelt is on, car is in neutral, feet are on the brake and you whistle the "star spangled banner" three times.
 
  • #19
Mech_Engineer
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Would fitting an electric fan instead of the engine driven one improve millage?
It might help a little, but not much. I swapped an electric fan into my old car and it helped with throttle response, but not mileage.

And air filters do the trick ones work better?
Don't use oiled cotton filters, they let more dirt in than a stadard paper one. If you want to use an aftermarket filter, use a reusable foam filter (oiled or oil free, depending on brand). They're a good idea more from a filtering and reuasibility standpoint than a mileage factor though.

Change to performance exhaust system?

Manufacturers fit the cheapest possible exhaust system, some performance exhausts claim 10 to 15 % better fuel economy through better exhaust flow and better cylinder scavenging.
Might help some, but that would be a case-by-case basis, and modern vehicles have gotten much more efficient exhaust systems in the horsepower wars so you probably won't gain much. There is no such thing as scavenging on a 4-stroke engine, exhausts are more (or less) efficient based on their backpressure, and its important to note bigger doesn't always mean less backpressure...

Running with lights on in day time increases alternator loading and thus power sapped from engine.
Sure, that might help. but like has been mentioned, even the hi-beams on a car pulling about 15 or 20 amps (at 12 volts) would only account for 0.2% of a 150hp engine's power output (but most hi-beams probably only pull about 13 amps total, 80 W each). If you're cruising down the road and only using about 30hp to maintain speed, 240W of light power would be a 1% increase in power draw.
 
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  • #20
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You would be amazed by how many people in the UK drive with head lights on, some even have extra spot lights on in perfect visibility.
Might they be driving Volvos, perchance? :biggrin:
 
  • #21
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curse of the modern CPU controlled fuel injection
that really limits the changes you can make
BUT you can rewire and use a program able unit like a megasquirt
but good luck getting better then major CORP did with their skilled staff
thats you vs a CORP full of pro's with almost unlimited funding

older cars with carb's could re-jet and run water injection on a lean burn
swap rear end gears and or use bigger rear wheels and harder narrower tyres

all are trade offs you loose braking and handling to gain a few MPG with narrower harder tyres

I guess the only real big gains are to swap the car for a newer smaller one
car pool or take a bus
 
  • #22
wolram
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There are some oils on the market that claim better performance, i do not have a link, but
some say there is a noticeable difference.
 
  • #23
Mech_Engineer
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curse of the modern CPU controlled fuel injection
that really limits the changes you can make
BUT you can rewire and use a program able unit like a megasquirt
but good luck getting better then major CORP did with their skilled staff
thats you vs a CORP full of pro's with almost unlimited funding

older cars with carb's could re-jet and run water injection on a lean burn
swap rear end gears and or use bigger rear wheels and harder narrower tyres
I wouldn't consider EFI a curse... The reason cars are so efficient these days is because they have computers that use closed feedback loops to measure AFR, spark knock, and other metrics and adjust accordingly. Running an engine with a leaner mixture is generally a dangerous thing to do IMO.

There are some oils on the market that claim better performance, i do not have a link, but
some say there is a noticeable difference.
Marketing gimmicks I would think. Using higher quality synthetic oils can help prolong the life of your engine by reducing wear and/or extending preformance of the lubrication system, but I doubt that there is such a huge difference in internal friction that your mileage increases measurably.
 
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  • #24
wolram
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Do these electronic box es control throttle input? ie give a nice rounded graph instead of a
spiky graph of the boy racer type, i imagine if one wanted PMG, sedate acceleration would be ok, so long as there is an emergency over ride like flooring the pedal.
 
  • #25
mgb_phys
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I always wondered why there isn't an economy mode on an automatic transmission.
You drive an automatic and it happily drops a gear when on a hill in to keep the same speed - wouldn't it be a simple software option to just allow the speed to drop by say 10-20% at the same revs while climbing?
 

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