Gas mileage

Reply

  #1  
Old 02-03-13, 04:26 PM
D
dam
dam is offline
Member
Thread Starter
Join Date: May 2005
Location: us
Posts: 51
Received 0 Votes on 0 Posts
Gas mileage

Is there a difference in fuel mileage between mid grade and regular?
 
Sponsored Links
  #2  
Old 02-03-13, 04:39 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,967
Received 5 Votes on 5 Posts
Probably no gas mileage difference, but performance difference. It will depend on what your car's manufacturer stipulates is the best fuel for your car that is important. Changing grades can, at best, waste money, and at worst damage emission systems.
 
  #3  
Old 02-03-13, 05:15 PM
T
Member
Join Date: Oct 2010
Location: USA
Posts: 563
Received 0 Votes on 0 Posts
Octane rating essentially provides a guide as to how much compression a given fuel can handle before the compression leads to premature detonation or pinging, which can cause engine damage. The higher the octane rating, the higher compression the engine can be without pinging.

Many modern engines have a device called a knock sensor, that will allow some modern fuel-injected vehicles to attempt to reduce or eliminate premature detonation by controlling spark or fuel delivery. When an engine detects excessive knocking or pinging it will reduce performance to reduce the pinging. That can possibly translate into fuel economy losses too, but not necessarily.

One should generally run the lowest octane that one's engine can use without pinging, which is what the manufacturer specifies when they sell the vehicle new. If your owner's manual says that it's just fine to use 87, then use 87. If it says 89 or 91 perferred but that 87 is acceptable in some circumstances if higher isn't available, then probably run whatever is preferred.

The use of higher-than-necessary octane fuel provides no benefit. The engine isn't going to run more or less efficiently because of a different octane rating, one is only going to spend more money.
 
  #4  
Old 02-04-13, 06:18 AM
N
Member
Join Date: Jan 2012
Location: Canada
Posts: 2,744
Received 18 Votes on 16 Posts
T-W-X pretty much covered everything.

The simplistic answer is... If it's fuel injected, it should have a knock sensor. If it has one, run the recommended Octane rated fuel. The computer with that sensor will adjust things to prevent problems.

Keep in mind, if your vehicle is rated for a high octane, running a lower octane level can do affect your milage and potentially cause pre-mature engine wear.
 
  #5  
Old 02-04-13, 06:36 AM
S
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 19,570
Received 94 Votes on 83 Posts
There is an optimal octane rating for your car. Higher performance cars with higher compression in the cylinders will require higher octane and often will have performance and fuel economy degradation if lower octane fuel is used.

That said, my ex-wife had a 92 Honda Prelude when I met her and it became my car at one point - I noticed the sticker on the fuel door that said premium fuel was required so I thought I'd try some (we'd been only ever putting regular fuel in it) - my mileage got worse, so I quit that experiment after two tanks.
 
  #6  
Old 02-04-13, 09:51 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,967
Received 5 Votes on 5 Posts
Back when I was in college I had a '62 VW. Ran great. I thought I would "clean" the upper engine by running a tank of then Amoco White Gas. I think the octane rating was like 96+%. Finished that tank and noticed the tailpipes had fallen off Didn't do that again!! Too hot, I guess.
 
  #7  
Old 02-04-13, 01:22 PM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 47,542
Received 300 Votes on 266 Posts
Larry, I used to burn a tank full of white gas once a month - It did burn hotter but it kept all the key components clean! Unless I'm mistaken it was 100 octane. It was called white gas because it didn't have any lead added - if you can remember, leaded gas had a red tint.
 
  #8  
Old 02-04-13, 04:28 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,967
Received 5 Votes on 5 Posts
You're right, I do think it was 100 octane. Clear as moonshine.......I guess.........never..........well I heard..........
 
  #9  
Old 02-05-13, 04:54 AM
N
Member
Join Date: Jan 2012
Location: Canada
Posts: 2,744
Received 18 Votes on 16 Posts
You guys where running what we call Ava gas (aviation fuel, now about 110 Octane).
Runs hot and stinks when racing 2-strokes.
 
  #10  
Old 02-05-13, 12:04 PM
S
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 19,570
Received 94 Votes on 83 Posts
Used to have a neighbor with a hot rod he raced - had the compression up so so high that to go any higher would mean he'd have to move from gas to alcohol. You couldn't stand within 10' of the garage if that thing was running, the fumes would make your eyes water.
 
  #11  
Old 02-05-13, 01:50 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,967
Received 5 Votes on 5 Posts
You guys where running what we call Ava gas
Yeah, but it was available at your corner Amoco station back then. The cars we built back in the 60's had such compression that it was needed. Just wish kids nowadays had just a taste of the power we produced from stock (and modified) engines, with only 2 years of highschool under our belts at the time. Times gone by.
 
  #12  
Old 02-08-13, 11:16 AM
T
Member
Join Date: Oct 2010
Location: USA
Posts: 563
Received 0 Votes on 0 Posts
We once ran some low-lead airplane fuel in our Honda Fourtrax ATVs... Yeah, they ran hotter, but they did run faster...

Higher thermal coefficient of expansion means that the expanding, burning fuel pushes harder against the piston. More vroom.

To my knowledge, regular automotive fuel won't really differ that way.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: