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

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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.   :lol:

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
-wreckedcarzz (June 20, 2011, 10:25 PM)
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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.
-eleman (June 21, 2011, 01:52 AM)
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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.
-app103 (June 21, 2011, 02:25 AM)
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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.   :lol:
-techidave (June 21, 2011, 05:43 AM)
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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 :P

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?

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