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The (Don't Yawn!) Fuel Economy thread!

Sly said:
In the UK standard unleaded is 95 octane , super is 98 (BP) or 99 octane (shell).
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Most fuel stations in the US sell three grades - 87 (regular), 89 ("plus") and 91-95 octane (Premium). I have no idea why 89 octane exists, since all cars on the road are designed to run either 87 or 91+ octane fuels. Cars designed to run 91+ can use lower octane fuels but the ECM program that allows for this produces horrible fuel economy and lowered engine output.
 
Lord Blackadder said:
Really? I thought they switched to unleaded...Not sure though. I'm pretty sure avgas is legal to sell for non-road going cars (i.e. race cars).
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No, avgas is still leaded. Nobody has figured out a formulation of unleaded gas that won't damage the valves and seats of the ancient engines used in most general aviation airplanes. The newer airplane engines (e.g., Rotax) can run on unleaded (and even some of the old ones), but now we've got a new problem with the ethanol blended fuel. That stuff eats rubber. Car fuel systems can handle it, but many airplane fuel systems can't.
 
IJ Reilly said:
No, avgas is still leaded. Nobody has figured out a formulation of unleaded gas that won't damage the valves and seats of the ancient engines used in most general aviation airplanes.
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I saw somewhere that they sell 100 octane unleaded avgas, but that there are still a lot of users of leaded avgas. It makes sense...who wants to ruin the engine of their priceless P-51 Mustang with sketchy fuel? :eek:
 
Lord Blackadder said:
You know, I never knew what the fuel consumption of a Semi was...5.7mpg huh? Wow, I guess I figured it would be at little bit higher. What kind of fuel consumption does it have at idle?
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For some interesting reading check out the Cummins fuel mileage whitepaper. Pretty neat stuff there.

According to the white paper my truck uses about .5 GPH idling, its a fair tradeoff for keeping cool in the summer :) The truck has a diesel powered standalone heater that is used during the winter, I don't know how much fuel it consumes but it is MUCH less than running the engine. I don't idle between 20ºF and 70ºF.

I keep careful track of my fuel consumption, Here is a screenshot of the Fuel report for my new(slightly used) truck, a 2008 Kenworth T2000. And Here is a screenshot for my last truck, a 2008 Volvo VNL680.

Both trucks have the same engine, transmission, rear-end gearing, tire size and emissions equipment. The T2000 seems to have a slightly different program running in its ECU, it likes to rev a little higher. It also has brand new tires on it so that hurts things a bit.

I didn't start tracking mileage on the Volvo until 50k, but its tires were the originals so it has a slight advantage. I also idled the Volvo less because it was wintertime. It will be interesting to see what the numbers are as I figure out what this truck really likes and when cooler weather comes around so I can Idle less.

I'm also thinking about building a fiberglass under tray for the T2000 to see if smoothing out the airflow will make any improvement. I just sent a PM to a guy on another board who work at Paccar(the makers of Kenworth and Peterbilt) to see what his thoughts on the matter are.



I also have a '85 Mustang that gets 32-33 MPG on the highway and 26 combined with a heavy right foot. Its been "slightly" modified :D
 
Lord Blackadder said:
I saw somewhere that they sell 100 octane unleaded avgas, but that there are still a lot of users of leaded avgas. It makes sense...who wants to ruin the engine of their priceless P-51 Mustang with sketchy fuel? :eek:
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I don't think so. A lot of R&D effort has been put into finding a lead alternative for older airplane engines, but so far, nothing does the job like TEL. Here's a good summary of the state of affairs:

http://www.aopa.org/whatsnew/regulatory/regunlead.html

Which is none too good for owners of older airplanes, such as myself. I used to be able to burn the old 80/86 leaded which (ironically) had less lead in it than the current 100LL (low lead), but that stuff is history. I could also buy a Supplemental Type Certificate (STC), essentially a permit, to run car gas, but then I've got two problems: (1) they don't sell it at airports, and (2) ethanol.
 
For the big rig drivers:

Have any rig driver here heard any results about HHO kits (Brown's gas, hydrogen supplements, etc.)? A friend of my brother used one and says he got a 35% increase in fuel mileage. I've seen pre-built kits from a number of companies:

http://www.fuelfromh2o.com/

http://www.hydrogenht.com/index.html

There's a bunch of others; google HHO gas and you'll find more than you'd care to wade through.

I'm very curious to hear any results!
 
crazytom said:
Have any rig driver here heard any results about HHO kits (Brown's gas, hydrogen supplements, etc.)? A friend of my brother used one and says he got a 35% increase in fuel mileage. I've seen pre-built kits from a number of companies:

http://www.fuelfromh2o.com/

http://www.hydrogenht.com/index.html

There's a bunch of others; google HHO gas and you'll find more than you'd care to wade through.

I'm very curious to hear any results!
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#1) When engine costs $30k to replace without a warranty you don't want to make any mods that will void the warranty.

#2) Companies love anything that will give them a .5 increase in MPG, if HHO really provided a 35% increase in MPG without decreasing the engine life then every major truck manufacturer would be working on this technology. I haven't rear a word from any of them about it.
 
IJ Reilly said:
Which is none too good for owners of older airplanes, such as myself. I used to be able to burn the old 80/86 leaded which (ironically) had less lead in it than the current 100LL (low lead), but that stuff is history. I could also buy a Supplemental Type Certificate (STC), essentially a permit, to run car gas, but then I've got two problems: (1) they don't sell it at airports, and (2) ethanol.
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Ah, I suppose I was thinking about 100LL...still leaded.

When you say "older" airplanes, how old are we talking?
 
My car a 1994 Mercury Tracer trio, gets 40-43 miles per gallon in the summer. It drops to 37-39 in the winter. When it had the Goodyear Vectra tires on it, I averaged 44 mpg in the summer, and 40+ in the winter. Interesting what a tire change does.

BTW, I work for a school district and the new busses get about 7-10 mpg empty. For comparison, the older busses get 5-7 empty. Quite the change technology makes.
 
dmr727 said:
Sweet! What kind of airplane do you own?
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Lord Blackadder said:
Ah, I suppose I was thinking about 100LL...still leaded.

When you say "older" airplanes, how old are we talking?
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Mine is a 1968 Cessna 172, which about the average age for an airplane in the general aviation fleet. But the important factor is that the Lycoming engine in this airplane is essentially the same one used in many other airplanes for decades, both before and after. These engines really aren't the deal-breaker for unleaded avgas though, it's the high-performance ones that demand high octane juice.

Aviation technology changes very slowly, and even more so because airplanes tend to continue flying virtually forever, if they don't get wrecked.
 
IJ Reilly said:
For all practical purposes, whenever the clutch is engaged or you are between gears, you're in neutral. As for it being better to be in neutral, I am assuming (for lack of any evidence to the contrary) that adding engine braking slows the car more quickly, so if the objective is to make the most out of momentum, then taking the car out of gear would be the most effective way. Apparently some are arguing that cars use more fuel coasting at idle than they do coasting in gear. I don't see how that can be true (it seems counterintuitive), but I'm open to persuasion if some hard evidence is presented.
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When you are in neutral, you need some fuel to keep the engine running. When you are coasting in gear, the momentum of the car keeps the engine running. Obviously this will slow you down, but you don't use _any_ fuel (on newer engines). I drive some roads that go downhill with a stop necessary at the end, so I coast in gear because otherwise I get too fast and have to brake on the way down, and it uses no fuel at all.

On the other hand, there is one stretch on my way where it goes downhill very slightly and I can just about coast in neutral at constant speed (using fuel); coasting in gear would mean that I slow down (using no fuel).
 
gnasher729 said:
When you are in neutral, you need some fuel to keep the engine running. When you are coasting in gear, the momentum of the car keeps the engine running. Obviously this will slow you down, but you don't use _any_ fuel (on newer engines). I drive some roads that go downhill with a stop necessary at the end, so I coast in gear because otherwise I get too fast and have to brake on the way down, and it uses no fuel at all.

On the other hand, there is one stretch on my way where it goes downhill very slightly and I can just about coast in neutral at constant speed (using fuel); coasting in gear would mean that I slow down (using no fuel).
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The fuel required to keep the engine running out of gear is what's required at idle speed (around 800 RPM), which I'd consider to be the minimum possible fuel consumption. I'd like to see some documentation that coasting in gear uses less fuel (none, you say?), than coasting at idle. Either way, to calculate which method is more fuel-efficient, you'd also need to consider the effects of engine braking in the amount of distance which can be covered. I'm reasonably confident that my car will roll to a stop in a shorter distance in gear compared to out of gear.
 
IJ Reilly said:
I'd like to see some documentation that coasting in gear uses less fuel (none, you say?), than coasting at idle.
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I don't know this to be true, but if a modern fuel injected car is coasting in gear, it should be possible to shut off the fuel flow while engine braking - as long as the engine speed doesn't drop below the stall speed the fuel flow can be turned back on when you stop engine braking without the engine stalling. Just a guess. The difference between this and idling would be negligible I would think, though it would improve efficiency over traditional engine braking, where you are burning plenty of fuel while engine braking.
 
IJ Reilly said:
n. I'd like to see some documentation that coasting in gear uses less fuel (none, you say?),
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Just look up infomation on modern cars or if you car has a full mileage indicator on it compared them when running down a hill in gear compared to out of gear.

While yes you car will travel slow down faster in gear compared to out of gear. Gas mileage wise when in gear it does not burn gas while engine breaking. Compared to in netual is has to.

Reason for this is a modern fuel injected car just turns off the injectors when they are not needed. Hell on top of that the car will just recycle the exhausted to burn it even some more. This farther reduces how fast your filter clogs up because it does not suck in more are.

On even a more modern car it will turn off the sparks plugs
 
sorry i'm late in this argument, but i must add my $0.02.

coming from someone who has only owned manual transmissions, and was taught to 'keep your foot off the clutch as much as possible' = save the clutch

of course that makes the brakes wear out much sooner.

i am in neutral coasting as much as possible. i don't care what people say, coasting is the best way to save gas - and i have proof - i have a scangauge, and it tells me i'm getting 200 mpg coasting down a hill, while only 100 mpg in gear coasting down the hill.

i was taught to switch gears earliest as possible, take turns in 3rd and 4th gear if possible, and coast when possible.

and yes, coasting is illegal, and police used to be able to track with radar, but now that they use lazer technology, it doesn't. (i'm not quite sure about this part though)

anyways, coasting can be dangerous, and does wear your brakes out faster, but i'd rather replace my brakes for $100 than pay $800 for a new clutch. (and save gas in the process)
 
twoodcc said:
sorry i'm late in this argument, but i must add my $0.02.

coming from someone who has only owned manual transmissions, and was taught to 'keep your foot off the clutch as much as possible' = save the clutch

of course that makes the brakes wear out much sooner.
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You do nkow the clutch only wear when it slipping. When it is fully engage and fully disenage it is not wearing at all.

Now holding it disegage with the clutch pedal dues put a lot more stress on other parts of the clutch that general will out last a clutch plate any how but are always replaced with the clutch.

Just though I put that in.
 
Lord Blackadder said:
Most fuel stations in the US sell three grades - 87 (regular), 89 ("plus") and 91-95 octane (Premium). I have no idea why 89 octane exists, since all cars on the road are designed to run either 87 or 91+ octane fuels. Cars designed to run 91+ can use lower octane fuels but the ECM program that allows for this produces horrible fuel economy and lowered engine output.
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89 octane gas provides better fuel economy than 87, and is almost required for vehicles originally designed for leaded gas, as it prevents knocking similarly to how the tetraethyl-lead additive in leaded gas did, and most of those vehicles are too old to be worth the extra cost of Premium. My Taurus drives much better using 89 or 91-4 than with the 87, even though 87 is what is recommended.

Also, AFAIK, the octane ratings between the US/Canada and EU are found using different formulas. I had a friend who had a VW Bus, and ordered some replacement parts from the EU, and got a German labeled fuel door, which suggested 97 octane for the vehicle, which using the US formula would be nearly impossible to find.

Also, in the Mountain States of the US, the octane ratings for the gas is lower. Regular Unleaded is 85/85.5, Plus is 87, and Premium is 89 (or if you are lucky 91).

TEG
 
Rodimus Prime said:
Now holding it disegage with the clutch pedal dues put a lot more stress on other parts of the clutch that general will out last a clutch plate any how but are always replaced with the clutch.
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Stop-and-go traffic can put a lot of wear on the throw out bearing, because you are holding the clutch in a disengaged position a lot more often than you would in normal driving. I've never had a problem with it, but if you are a careful driver that gets a lot of miles out of a clutch than it's conceivable that you could wear out the throw out bearing before the pressure plates.

TEG said:
89 octane gas provides better fuel economy than 87, and is almost required for vehicles originally designed for leaded gas, as it prevents knocking similarly to how the tetraethyl-lead additive in leaded gas did, and most of those vehicles are too old to be worth the extra cost of Premium. My Taurus drives much better using 89 or 91-4 than with the 87, even though 87 is what is recommended.
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I experimented with 89 octane in my Toyota trucks and Nissan Altima (they recommend 87), and the result was a wash - no increased fuel economy. My father's 2001 Nissan Maxima would do about 21-23mpg on 91-95 octane, and about 17-19mpg on 89 octane. One of my friends was forced to use 89 in his Integra GSR on a road trip and he lost several mpg as well.
 
Lord Blackadder said:
Stop-and-go traffic can put a lot of wear on the throw out bearing, because you are holding the clutch in a disengaged position a lot more often than you would in normal driving. I've never had a problem with it, but if you are a careful driver that gets a lot of miles out of a clutch than it's conceivable that you could wear out the throw out bearing before the pressure plates.
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I did this once, on a Ford Pinto I owned in college. IIRC, it started to make a chirping sound with clutch engaged. Bad throw-out bearing. Well, bad car all-around, really.

Got to comment on the idea that cars "run better" on fuel with a higher octane than required. I thought this fallacy had been completely debunked years ago. Even in cars for which higher octane fuel is recommended, they will run fine with a lower octane. Modern engines are electronically controlled to prevent valve knock, and the loss of engine output is virtually unmeasurable.
 
Rodimus Prime said:
You do nkow the clutch only wear when it slipping. When it is fully engage and fully disenage it is not wearing at all.

Now holding it disegage with the clutch pedal dues put a lot more stress on other parts of the clutch that general will out last a clutch plate any how but are always replaced with the clutch.

Just though I put that in.
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i do know that. but when it is fully engaged, it is the same as you being in neutral
 
Lord Blackadder said:
I experimented with 89 octane in my Toyota trucks and Nissan Altima (they recommend 87), and the result was a wash - no increased fuel economy. My father's 2001 Nissan Maxima would do about 21-23mpg on 91-95 octane, and about 17-19mpg on 89 octane. One of my friends was forced to use 89 in his Integra GSR on a road trip and he lost several mpg as well.
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Using 89 depends on what kind of 89 it is. If you live in the Midwest, 89 is actually 87 with Ethanol added to boost the octane to 89 but with much less power than 87. I use 89 when someplace where all blends are equal, but avoid it like the plague when 89 is E-10. I usually get about 24 using 87, but get 28 using 89 (when not E-10).

TEG
 
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