Non-tech, off-the-wall topic: Gasoline/Petrol, does grade matter?

[wreckedcarzz]

Okay, I know this is wayyyy off the beaten path of anything even remotely tech-related, but it's been itching at me for a while. I hope it isn't too non-techy for DC

As some of you may know, I'm a teenager. And, as you also may know, teenagers tend to drive. A lot. All the time. Sometimes every day! And while most of them drive a small vehicle like a Honda Accord, a Ford Escort, or something of the like (from who I know), some of them can occasionally be seen in not-so-gasoline-friendly vehicles. Such is the case for myself. Almost every other day I go hang out with friends in my dad's vehicle: a 2001 Chevy Silverado HD2500 crew cab pickup truck. And being such a large vehicle, it consumes gasoline fast enough that one may think that the gasoline is literally set ablaze in the tank when you turn the key in the ignition.

My dad tells me the fuel economy is the same going uphill pulling a trailer full of cattle, or downhill with no trailer with no cattle, and the wind pushing you down. I have verified the fact that mashing the gas at green lights, versus gentle take-offs, has absolutely no noticeable effect on fuel consumption either (this was done with several tanks of gas to nullify other factors in play). Aside from obtaining a smaller vehicle (which I am in the process of doing ) I need to increase the fuel economy on this truck for the time being, so I started to wonder if the fuel grade matters enough to put Plus or Premium in instead of standard Unleaded?

TL;DR
Does the grade of gasoline/petrol you put in your vehicle make a noticeable impact on fuel economy, and if so, where do you go to purchase said fuel? I'm stateside so not sure if anyone outside of the US can help my specific problem, but you could help someone else by posting regardless

-Brandon

EDIT: Right now, I'm getting 6 miles to the gallon. The truck is rated for 8. Even if I can pull it back to 8 that is a 25% increase in money staying inside my wallet.

[techidave]

Ask a racer if Premium grade performs  better than the standard stuff.  I am confident he will tell you it will.

we lived in Dallas, TX for 5 years.  down there they use reformulated gasoline or as I call it, recycled gas.    They use it to supposedly combat smog.  The part they don't tell you is your car gets poorer mileage, harder to start, and runs crappier as a general rule. They mechanics down there will tell you to use a higher grade of gasoline.  I do believe most larger cities have gone to this.  I know that Kansas City was talking about it a couple of years ago, so I assume they have went to it.

On our trips home to Kansas, roughly a day's drive, my car started running better on the second tank of fuel through it.

There have been many gimmicks "invented" over the years to increase gas mileage.  95% of them didn't work or were very dangerous to use.  I believe you would be better off getting a vehicle that was designed for better MPG.

By the way, in my opinion, I disagree with your dad and with your experiment.  But everybody is entitled to their own opinion.

Dave

[mwb1100]

My understanding is that the various grades of gasoline (the different octane ratings) have nothing to do with fuel economy or how much 'power' or 'juice' the fuel has.  The octane rating is a measurement that indicates how resistant the fuel is to detonation from compression.  If the fuel detonates to early when the the fuel-air mixture is compressed, you get 'pinging' or 'knocking' and that will hurt fuel economy (and can cause further problems).

Basically a higher octane fuel can handle a higher compression - that's why high performance engines will require a high octane fuel; they're designed to use higher compression (as that can give's more power).  But just using a higher octane fuel without changing the compression in the combustion chamber will not provide any more power - you're just wasting money.

If your engine exhibits knocking, then using a higher octane fuel might help with that problem, but aside from that, probably no benefit.

It's possible that the oil companies might claim that the higher grade of fuel also has other additives that might provide some benefit, but I doubt that's anything more than marketing.

[Shades]

6 miles per gallon...that is around 10 kilometers. A gallon is slightly more than 3 liters, so that comes to a result 3 kilometers per liter of fuel.

Amazing! In a bad way. I expect to see those numbers when a truck is hauling 30.000 kilos of freight.

The sound of American engines (muscle cars), that is how heaven could sound like. But the consumption is appalling. Darn, combustion engines in cars should already be driving 100 kilometers per liter to be sustainable.

Ok, more ontopic now:
To my understanding, the quality of fuel does matter. Not necessarily in consumption, but also for maintenance. Here in Paraguay there is a fuel called 'Flex' and is sold for practically the same price as diesel (slightly over 1 USD/liter). But you can run your engine completely down if it doesn't "support" it.

For my motorbike I only use the good fuel (about 1.5 USD/liter) as I notice that the engine is more responsive and generally sounds nicer.

Granted, all this is anecdotal, so your mileage may vary...or not in the case of your dad's truck.

I never understood the US and their stance against diesel. Especially the distances one has to travel over there. In the Netherlands I had diesel cars that easily drove 20 kilometers/liter, even one that had no problem getting to 25 kilometers/liter. That particular Peugot 205 was from 1986, strong, dependable and a joy to drive. So it is not impossible to get way better mileage, even with old technology.

Ah well, this post is starting to become a nagfest, I'll stop.

[eleman]

Here are a few general tips about fuel economy. There are no miracle cures like "pump gas for 2 seconds, hit the brake 3 times and signal to the left and your milage will increase by 50%". Fuel economy is more about the car (smaller the better, diesel the better, newer the better), and also about driving with less adventure.

For instance, when you think you will have to stop at a red light, leave the gas alone, and let the vehicle drift to a stop. Do not increase your speed and hit hard brakes upon the red light.

I know these are no brainer, but I have trouble making wifey apply such principles

That being said, higher grade (or octane) does not help fuel economy. See wikipedia.

[app103]

Every car comes with an owner's manual that specifies the octane that should be used. Follow that as your guide. Too low and as mwb1100 said, you'll get knock & ping, which isn't good for your engine. Too high will also not do your car or wallet any good. Both will shorten the life of your car.

If you follow the owner's manual and the octane they recommend causes a problem, go up to a higher octane only long enough till you can get the problem fixed, so you can go back to what you should be using.

[techidave]

Maybe the truck is in need of a tune up!    You don't say if the pickup is four wheel drive or not but that will affect your mileage.

My 2001 Chevy S-10 4.3L V-6 Extended cab gets around 17 city to 22 highway.  I sure thought I would get better than that when I bought it.

Vehicles are rated for mileage under the best of conditions, of which, we will never see out in the field.

This could go on and on but to avoid an ... I am done commenting on it. 

[AndyM]

My dad tells me the fuel economy is the same going uphill pulling a trailer full of cattle, or downhill with no trailer with no cattle, and the wind pushing you down. I have verified the fact that mashing the gas at green lights, versus gentle take-offs, has absolutely no noticeable effect on fuel consumption either

This is simply not correct.

mwb1100's explanation of octane ratings is spot on.

[CWuestefeld]

Just to chime in:

AndyM is correct in contradicting your dad. Fuel is burned to create motive force. In Newtonian physics, force = mass * acceleration. Given a constant mass for your car, the amount of fuel burned (ignoring the efficiency curve of your particular drivetrain) is proportional to the total amount of acceleration you're demanding of it. When traveling down a hill with a tailwind, you're not asking the engine to provide acceleration, while uphill (and with a trailer) that demand is greatly increased.

And mwb1100 is also correct. The "octane" reflects the amount of octane molecules; you may notice that the word sounds somewhat like "methane", "butane", "propane", etc. These are all different petroleum compounds. The octane one happens to require a greater amount of energy to stimulate its oxidation reaction. When there is more ambient energy, in particular, when the pressure is greater (remember, PV=nRT, so the compression cycle of the cylinder, where volume decreases, is pretty much equivalent to cranking up the temperature), then other petroleum molecules are prone to ignite before the cylinder head has moved to the optimal position. This early ignition (a) lowers fuel efficiency, since the explosion is fighting against the cylinder head getting down to that bottom position; and (b) increases pressure even further, creating more heat that can actually damage the engine.

In older cars, these premature ignitions can be perceived as a "knock" or "ping" sound. In newer cars, the engine has a knock sensor that will notice this before you can. In such a case, I believe the engine will compensate by changing the timing of the ignition spark, or dumping extra fuel into the cylinder in an effort to lower the temperature and stop the premature ignition -- thus lowering your fuel efficiency even more.

So, by using a fuel mixture with a higher proportion of octane molecules, you avoid this problem.

All that said, it's only an issue if the degree of compression in your engine is high enough that "normal" gas is in danger of that premature ignition. This is the case in a small minority of normally-aspirated engines (the Toyota FJ comes to mind). But if you've got forced induction (i.e., a turbocharger or supercharger) increasing the pressure, then you probably need high-octane gas.

If you don't have a car whose engine is susceptible to the problem, then paying for that extra resistance to ignition is wasted.

[wreckedcarzz]

For instance, when you think you will have to stop at a red light, leave the gas alone, and let the vehicle drift to a stop. Do not increase your speed and hit hard brakes upon the red light.

I usually do that, because of the weight the truck will drift along around 35-40MPH (the usual speed limit here) for a quarter mile easily. I've gone through a tank driving very very economical, and very "non-economical" and I didn't notice any difference in how many miles I got out of the tank. This is confusing me; is it using up extra fuel even when I'm not telling it to?

Every car comes with an owner's manual that specifies the octane that should be used. Follow that as your guide. Too low and as mwb1100 said, you'll get knock & ping, which isn't good for your engine. Too high will also not do your car or wallet any good. Both will shorten the life of your car.

It says use standard Unleaded, which kind of surprised me for something that size. Other than the crappy fuel economy, there aren't any problems with it at all. It's disheartening to drive something in such good condition but you can only drive 3 blocks and back for ~$3.41

Maybe the truck is in need of a tune up!    You don't say if the pickup is four wheel drive or not but that will affect your mileage.

My 2001 Chevy S-10 4.3L V-6 Extended cab gets around 17 city to 22 highway.  I sure thought I would get better than that when I bought it.

Vehicles are rated for mileage under the best of conditions, of which, we will never see out in the field.

This could go on and on but to avoid an ... I am done commenting on it. 

I mentioned it to my dad about 2 weeks ago and he told me we'd take it down and get it done "soon." So it may not see one for several months

It is a 2x4, also. He last had an AWD "dually" truck (two rear wheels per side) so I have no idea what he got in that thing.


CWuestefeld:
I am surprised I was able to understand that. Useful information, summarized. I dunno about my dad sometimes, but he brought it up a few months back when I complained so I figured I would mention it. All I can vouch for is the awkward equal usage of gentle vs mashing acceleration.



So essentially it would only help if the engine demanded it or was changed to utilize it, which it is not. So it would simply be additional wasted money?

[JavaJones]

In regards to why "coasting to a stop" might not be having a noticeable effect on your fuel mileage, I'd say it's probably because it's so bad already, that even a 10% improvement (which would be quite dramatic for something as simple as coasting instead of using brakes more) would only give you about half a mile per gallon, which you probably wouldn't even notice. Whereas for a car that already gets say 30mpg, a 10% improvement gets them 3mpg extra. In other words your baseline is so bad that almost no matter what you do it's not going to make a really *big* difference in terms of your fuel cost. Even if you *double* your mileage, you're still only getting 12mpg, which is well below an average car these days, and still quite poor.

- Oshyan

[wreckedcarzz]

Oshyan: Valid point as to why it could be I'm not seeing a difference. Though, at this rate, I'd be the happiest person ever to get 12MPG

[JavaJones]

Hehe, of course. But doubling your mileage is essentially impossible with the vehicle you have of course. The point was that even doubling your mileage would still be pretty bad! Hehe. If only you could borrow against your future fuel consumption, you'd have a new car in no time! Hey, that's not a bad idea...

- Oshyan

[cmpm]

A tuneup is a need for sure if you have not done that,
it seems to be lacking efficiency.
Get hotter burning plugs when you tune up, check the parts store for the best ones.

And the less you press the gas pedal the less you will burn gas.
That is a fact.

If it's a standard transmission, try not to wind out the gears.
Shift at lower rpms.
Even with automatics you can let the transmission shift at lower rpms.

Raising the air pressure in the tires to the maximum will get better mileage.
Debatable to many, but I've seen the difference.

Get the front end aligned, with such large tires they need to be near perfect.
If it's used for snow plowing, I'm sure the front end is a mess.

[JavaJones]

Yet with all that about the best you can hope to achieve is the manufacturer rated 8MPG! Ya needs a more efficient vehicle, no way 'round it.

- Oshyan