Ask the Car People.SM


What about fuel types & gas mileage?

297 messages,  Last post on Jan 20, 2013 at 2:20 PM

You are in the Maintenance & Repair Forum.

What is this discussion about? Engine, Fuel System

Messages Page 25 of 30

#237 of 297 Re: I got puished for trying [wai] by shipo

Jun 18, 2006 (10:30 am)

Replying to: wai (Jun 18, 2006 4:58 am)
Some cars' manual or fuel door sticker stated "require a certain MINIMUM Octane" Does it mean you should use fuel with that Octane or higher, but not lower.
 
The only correct answer here is, "It depends."
 
If any given engine is optimized for 91 octane but has ignition control electronics that allow it to retard the spark event for more volatile fuels (lower octane) and/or advance the spark event for less volatile fuels (higher octane), then the "Minimum Octane" in the manual might could well be 87. That having been said, that same engine will lose both performance and economy when anything less than 91 is being used.
 
The flip side of course is when any given engine is optimized for any given octane rating and then a higher octane fuel is used. In this scenario, performance and fuel economy will suffer if the engine isn't able to advance the spark event sufficiently to start the fuel burn early enough. If, however, the engine can advance the timing, economy and power may actually improve slightly, of course, not as much as an engine optimized to burn said higher octane fuel.
 
Best Regards,
Shipo

#238 of 297 Re: I got puished for trying [shipo] by wai

Jun 21, 2006 (12:39 pm)

Replying to: shipo (Jun 18, 2006 10:30 am)
Do you know that my Jetta 04 VR6 has ignition control electronics to advance the spark event for higher Octane fuel or not?

#239 of 297 Re: I got puished for trying [wai] by shipo

Jun 21, 2006 (1:56 pm)

Replying to: wai (Jun 21, 2006 12:39 pm)
Do I know? No.
 
I had a VR6 in my 1995 Passat and on that engine I don't remember it being at all sensitive to fuel above 91 or 92 octane.
 
Sorry I can't be more help than that.
 
Best Regards,
Shipo

#241 of 297 Gasoline providers by dtownfb

Feb 09, 2007 (12:02 pm)

I'm not sure if this is the right forum but hopefully someone can educate me on gasoline providers.
 
I live in an area where the gas stations are dominated by the local convenience stores, Rutter's, Sheetz, Tom's, etc. Reading a few forums, the discussion of top tiers gasoline providers popped up. It dawned on me that none of these providers are in my area (South Central PA) or are they? Is there a way to find out who provides the gas for these stations? Obviously Rutter's and Sheetz don't own refineries and must buy from someone.

#242 of 297 Gasoline providers by jaydh

Feb 13, 2007 (12:27 am)

These are most likely UNBRANDED providers who load up their trucks at the local refinery and sell to local convenience store chains, among others, in your area. It's basically the same gasoline that you would find at the branded stations.

#243 of 297 Gas Milage by calisteel

Jul 10, 2007 (5:29 pm)

I read a lot of car forums for many different reason. But there seems be a common post in just about all the forums, GAS MILEAGE.
 
Many people get upset or can not understand why the GAS mileage of same vehicles differs so much. It is quite simple and it is not what most people talk about. Yes how you drive has a lot to do with it but the one main reason that mileage differs on two like vehicles is ALTITUDE.
 
ALTITUDE will determine how lean or rich your car will run. Higher altitude will provide better gas mileage if your car is tuned properly for the higher altitude.
 
Here is a simple explanation of what I mean.
 
With altitude, air density decreases, so a computer controlled fuel injection system will automatically decrease the fuel in the mixture to match the air density. Thus all the electronic sensors needed to keep the motor running correctly. You will find that horsepower will decrease, but mileage will actually increase.
 
This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing.
 
I hope this help explain why gas mileage is so different from so many people. The higher the altitude the better mileage. So people in Denver get better mileage then people in Death Valley California.
 
If you need a better explanation your local mechanic can also explain this to you.
 
Cheers!

#244 of 297 Re: Gas Milage [calisteel] by imidazol97

Jul 11, 2007 (12:29 pm)

Replying to: calisteel (Jul 10, 2007 5:29 pm)
But the computer adjusts the amount of fuel to match the air and the load on the motor. The amount of unburned oxygen in the exhaust is measured by the O2 sensor and the car will have to do the same amount of work to move the car 1 mile so the same amount of fuel is going to be used.

#245 of 297 Re: Gas Milage [imidazol97] by calisteel

Jul 11, 2007 (12:52 pm)

Replying to: imidazol97 (Jul 11, 2007 12:29 pm)
Not true. At a higher altitude your fuel mixture will be less as well as your power output. You move the same 1 mile at the same rate but through less dense air, so less power is needed thus lessening the fuel needs as well.
 
In thicker or more dense air you need a more rich fuel mixture increasing the power output to move you 1 mile thus burning more fuel.
 
Even though the car is doing the same speed and distance the output of fuel needed is greater or lesser depending on the fuel mix based on air density. You can not get around it.

#246 of 297 Fuel Mix by imidazol97

Jul 11, 2007 (1:19 pm)

I thought the computer kept the mixture the same. The air valve in the throttle body lets more or less fuel mixture into the intake manifold to give more power.
 
What is the difference in air resistance at 900 feet altitude compared to 0 feet?

Messages Page 25 of 30

To POST a message, please Sign In.

Advertisement

Browse by Category

Browse by Vehicle
   View All Vehicles

Browse by Board
Browse by Topic
View All Topics

Edmunds Community

Advertisement