who gets mid-grade gas? why is it even sold? is it the economy?

12/17/2011 4:39:03 AM

Shouldn't really matter unless you're literally scraping pennies. A tank of mid-grade costs maybe $2 more than a tank of 87.

12/17/2011 5:07:42 AM

I've always wondered this

12/17/2011 9:09:02 AM

when an older motor that used to run fine on 87 needs 89 to avoid knocking under heavy loads.


and there are a few cars that required 89.

12/17/2011 9:34:56 AM

i always got mid grade for my jeep, actually i think it asked for it.. but my theory was always this... if i was a gas company and got water in my 93, i'd still sell it as 87.

12/17/2011 9:36:53 AM

i'm fucking tired of this misconception that octane rating has anything to do with quality

12/17/2011 9:38:41 AM

it doesn't , i know it has everything to do with knock resistance

12/17/2011 9:39:57 AM

that wasn't directed at you

[Edited on December 17, 2011 at 9:43 AM. Reason : pre-detonation]

[Edited on December 17, 2011 at 9:45 AM. Reason : so really the OP is kinda right]

12/17/2011 9:43:15 AM

people that put 93 in their late-model low-compression trucks/sedans make me

12/17/2011 10:50:11 AM

People that cause expensive engine damage by saving $2 a tank make me

12/17/2011 10:56:01 AM

and regularly using premium in a properly-running engine designed for 87, like 90% of the consumer vehicles on the road, can cause damage over time (small chance, but not non-zero). basically, read the damn manual. use what it recommends. filling your sports-package toyota camry with 93, at best, wastes money.

I get the utility of 89, I suppose, for those old beaters that are knocking badly. But seeing as those are fading into the junkyards and the new "old" cars have computers and knock sensors, I feel like 89 isn't relevant anymore. Save the service station real estate for regular and premium

[Edited on December 17, 2011 at 11:17 AM. Reason : asfd]

12/17/2011 11:07:17 AM

^^ If your engine isn't knocking and the manufacturer of the car calls for 87 octane, why the fuck are you going to put mid-grade or premium in it like a dumbass?

12/17/2011 11:16:15 AM

^

12/17/2011 11:36:47 AM

Quote :

"when an older motor that used to run fine on 87 needs 89 to avoid knocking under heavy loads. "

This. I had a beater '82 Malibu that would knock going up hills on 87 but was reasonably happy on 89. Also, some cars specifically state (in the manual/literature) that they are designed to run on minimum 87 but you will get better performance on 89/91/93. I seem to recall the Audi 5000S my family once owned made that sort of claim.

12/17/2011 12:12:11 PM

I wish they showed premium prices on the signs for gas station. it's really misleading to see 2.99 and 3.02 for 87 because you'd think the station with 2.99 would have cheaper 93, but it turns out a lot of times I pull up to a pump and see the 93 15 cents more per gallon than the 3.02 station

12/17/2011 12:38:59 PM

Quote :

"89 isn't relevant anymore. Save the service station real estate for regular and premium"

me thinks 89 is 87 and 93 mixed 50/50 so there is no extra real estate

12/17/2011 12:47:52 PM

^^^^^

additive package

But you can all feel free to run whatever you want in your engine. Gas is gas right? Be sure to buy up those little bottles of fuel injector cleaner at the store too when your tanks seems to be going empty faster since that will surely do exactly what it says.

[Edited on December 17, 2011 at 12:48 PM. Reason : I prefer Shell top tier]

12/17/2011 12:48:03 PM

^LOL. It's funny that you think a higher octane fuel=a higher quality fuel.

12/17/2011 12:51:20 PM

I never said that, but feel free to laugh now.

12/17/2011 12:53:49 PM

hey i missed this statement, care to qualify it?

Quote :

"and regularly using premium in a properly-running engine designed for 87, like 90% of the consumer vehicles on the road, can cause damage over time (small chance, but not non-zero)."

12/17/2011 1:00:58 PM

^^ So what is your reason for running a higher octane if your car does not need it? All you said was "additive package," which I am taking to mean that you are going with a more expensive fuel because of the additives in it that are supposed to keep the cylinder chamber and fuel injectors clean of carbon build up. These same "additives" can be found in 87 octane as well.

Of course you just eat into whatever bullshit TV ads will feed you. There may be marginal differences between different brands, but paying more per gallon for a higher octane fuel is just retarded.

And the likelihood of you fouling your injectors is slim to none, unless you have some piece o' shit from the 1980s.

12/17/2011 1:19:42 PM

^i'm pretty sure he's joking

12/17/2011 8:23:08 PM

gas quality isn't about octane level but rather the amount and type of additives different companies put in them, if you plan on keeping your car a long time it is probaly best to go with stations that sell shell, exxon, bp rather than pilot, kangaroo, hess

decent news story about it
http://www.abcactionnews.com/dpp/news/local_news/investigations/I-Team:-Test-of-different-popular-brands-of-gasoline-shows-big-differences-in-emissions-mileage

12/17/2011 10:37:43 PM

Quote :

"when an older motor that used to run fine on 87 needs 89 to avoid knocking under heavy loads."

Yep. Had an old Ford 2.9 that could have used a tune-up, but it got mid-grade or premium gas instead. It would ping like crazy when I stood on the accelerator going up hills with 87 octane in the tank, but it ran fine with the higher grade. Probably could have fixed it with minimal effort...Young and dumb.

12/17/2011 10:59:02 PM

Quote :

"hey i missed this statement, care to qualify it? "

for an engine designed for 87: high octane -> less combustible -> occasional incomplete combustion -> increased deposits -> decreased efficiency -> damage over time

Source: J. Blowme, et al. Hearsay and Conjecture. Phys. Ed. 23, 2011. 784-789

12/18/2011 1:30:28 PM

higher octane ratings do not imply lower combustibility of the fuel. In reality, the exact opposite is usually true. the extremely high octane race fuels have burn rates that are much higher than those of 87 octane fuels.

12/18/2011 1:47:28 PM

burn rate != combustibility

I'm talking about point of ignition conditions


i.e. imagine what'd happen if you put race fuel in a geo metro


this is a neat little snippet http://www.popularhotrodding.com/tech/0901phr_difference_between_pump_race_gas/index.html

[Edited on December 18, 2011 at 1:56 PM. Reason : sdf]

12/18/2011 1:48:35 PM

K I am imagining a Geo Metro that runs like a raped ape. Or any number of irrelevant scenes.

You can continue to think there is no point in premium fuel if you want, no one here will stop you from putting 87 into your tank.

12/18/2011 1:56:28 PM

are you trying to imply that the additive in higher octane fuel leave behind more residue then? because that's not true either.

The only disadvantage to running higher octane fuels is that they tend to contain less energy and could result in slightly lower fuel economy in some cars. everything else is just redneck gossip.

12/18/2011 1:58:36 PM

^^now where'n the hell did you get that I don't see a point in premium fuel? Higher octane fuel is obviously necessary in high-performance engines. I'm just saying that all you're doing is wasting money by putting it in your average grocery-getter

Quote :

"are you trying to imply that the additive in higher octane fuel leave behind more residue then"

no. I'm saying that higher octane fuel resists combustion more than regular and that can lead to unburnt fuel deposits in the engine. Will it always? no, especially not in an engine that's running properly. But take an older car that's limping along with a host of other issues and it could potentially be counterproductive


[Edited on December 18, 2011 at 2:02 PM. Reason : sadf]

12/18/2011 1:58:52 PM

My wife's Volvo requires "mid-grade". With 87 in it it pings really bad under load, but 89 or 93 works like a champ so we use 89 in it.

12/18/2011 2:00:06 PM

12-17-2011

never forget

today, we are all Garage posters

12/18/2011 2:04:16 PM

i have to run 93 in my corvette. I've had the engine tuned for a higher octane. Anything lower would cause knocking and loss hp.

12/18/2011 2:04:43 PM

Quote :

"no. I'm saying that higher octane fuel resists combustion more than regular and that can lead to unburnt fuel deposits in the engine"

Higher octane fuels don't resist combustion better; they only resist detonation from elevated temperature and pressure better. Most formulations for higher octane fuels actually burn faster once ignited.

12/18/2011 2:22:41 PM

^^ I actually run 87 octane in my C5 Z06 when I'm on interstate road trips...it cuts the power back due to the knock sensor telling the ECU to pull timing, but for idling down the interstate at 80 mph, who cares? Haha, shit, even if I lost 250 hp (which I don't), it would still be plenty adequate, hahaha.

In normal driving, I obviously run 93 in it.


In something like my old supercharged S2000, I would never run less than 93 for any reason (something like 11.5:1 CR, 6 psi of boost). I don't know if the ECU could pull enough timing in stock form; with SC boost, all bets would certainly be off.

[Edited on December 18, 2011 at 7:58 PM. Reason : in a car that only needs 87, I run 87.]

12/18/2011 7:58:09 PM

I read Oil 101 lately.

They don't have tank for the mid-grade. They just mix the other two blends as you pump it

And you can have an Octane rating of >100

That book shattered my world. Oh, but we're still all going to die in oil wars. That hasn't changed.

12/18/2011 8:05:02 PM

nascar used 110 octane at one point, now they use 98 they get a sweet 5 mpg

12/18/2011 8:25:22 PM

Quote :

"i'm fucking tired of this misconception that octane rating has anything to do with quality"

i won't lie, i used to think this was the case when i was in my teens...for the first year i had my first car (a '94 probe GT), i'd fill it up with 93 every oil change thinking it would burn cleaner and "clean out the gunk"

i don't recall anyone actually telling me that, but it's what i thought...of course, gas was not much over $1/gallon and 93 was only $0.10 more than 87 per gallon, so it wasn't a huge deal

12/18/2011 8:25:58 PM

gas stations around here have 85/87/91 i think. or maybe it's 89. not really sure. i just know i lived in CO for months before i even noticed that i was putting 85 in my car. i figured it had something to do with the cold weather. *shrug*

[Edited on December 18, 2011 at 8:37 PM. Reason : or higher elevation or something]

12/18/2011 8:33:22 PM

12/18/2011 8:42:33 PM