87 vs 91 fuel mpg differance?

[Jako]

First tank of gas was put in by dealer. Do not know what octane. Second tank was filled with 89. I only have 445 miles and have not used the tank of 89 octane. However, after filling the tank with 89 my mpg showed 23-24.3 mpg at a steady 50 miles an hour with cruise control for 6 to 7 miles. Not a large sample or very scientific but I was surprised by the mpg as compared to the prior tank of gas.
First tank of gas vehicle registered 18.5 mpg, hand calculation 16.78 mpg. In line with my 2001 Dodge Ram 1500 calculation differences.

 

[Gman]

Yes, the Premium is likely overkill, but for me it is a good .20¢ *cheaper* at Costco than Midgrade anywhere else... and Costco does sell TOP TIER gas.

That's a win-win.

 

[AnthonyD1978]

Yes, the Premium is likely overkill, but for me it is a good .20¢ *cheaper* at Costco than Midgrade anywhere else... and Costco does sell TOP TIER gas.

I know what my target #s are for this experiment... I'm willing to spend and extra .20¢ a gallon through a couple of tanks to see if there is a difference.

I'm just waiting for Amazon to get into the gas business

 

[VdMer]

Once you're compressed fuel is stable, what value do you get for making it more stable than required?

The recommendation for best performance and fuel economy in the manual is using a "Plus" grade. That doesn't mean "Premium".

There is no assurance in the manual that you will get better MPG.

...but it's your money, spend it where you want.

One of the best bits of info on fuel selection in the manual is this;

Besides using unleaded gasoline with the proper octane rating, gasolines that contain detergents, corrosion and stability additives are recommended. Using gasolines that have these additives will help improve fuel economy, reduce emissions, and maintain vehicle performance.

Second this. Quality, if anything, does matter, I think I saw Costco on this...though I do not use them as others do. http://clark.com/cars/top-tier-gas-stations-clean-engine-aaa/

 

[Gondul]

Second this. Quality, if anything, does matter, I think I saw Costco on this...though I do not use them as others do. http://clark.com/cars/top-tier-gas-stations-clean-engine-aaa/

Costco is indeed on the TOP TIER list.. however, they only sell 87 or 91... and the 91 at Coscto is cheaper than the 89 elsewhere, so...

 

[Jako]

89 octane, 800 miles, 65 mph and under, 80% highway-little city driving. Display 21.72 mpg - Hand Calculation 19.51 mpg. Utilized cruies control and was conscious of mpg while driving. Bighorn odometer has 1200 miles after trip from SE NY to NW NY and back - hilly terrain.

 

[kjn86]

I just went deep into the quality differences between certain gas irrespective of the octane rating. Going to try some different gas stations all at 89 and see if anything comes of it.

 

[Gman]

Going to try some different gas stations all at 89 and see if anything comes of it.

Everybody needs a hobby.

 

[Electrical]

The experts will tell you it's not related to the octane.

I'll tell you that even if it was, you got 10% better economy at a cost of 20% extra per gallon. Not a win.

If I get 50 miles more per tank, that is absolutely a "win"... unless you enjoy more frequent fill-ups.

I personally do not give a flip what the costs are.

 

[RAMDJ]

I'm just waiting for Amazon to get into the gas business

OR, maybe one of those services, like Chewy's or dollar shave club for gas. Where you pay a subscription and every 3-4 (depending on your subscription) nights, a gas truck stops by and tops off your tank.

 

[Kamikaze6780]

That's two votes for 2 mpgs more with higher octane......
Like @Gondul said....it's a wash for cost ultimately, but its interesting that other folks are confirming what I'm seeing with the uptick....again, could all be coincidence.

Psychologically they could be feathering the gas pedal after getting higher octane. Like the person that buys a new $500 pool stick, somehow he shoots better, but it's not the stick, he is just concentrating more for each shot.

 

[Gondul]

Psychologically they could be feathering the gas pedal after getting higher octane. Like the person that buys a new $500 pool stick, somehow he shoots better, but it's not the stick, he is just concentrating more for each shot.

Anything is possible out of a absolutely controlled envrionment... but I'm driving it pretty much the same way. No jack-rabbit starts, 5 over the posted speed limit (no interstate travel yet), if the light ahead is red I slow down hoping it will change but this is really dependent on traffic conditions.

After 4-6 tanks, I'll be going back to 87 (from Costco) to see what, if any, difference there is between the two...

 

[19Jake]

goin' back to Costco 87

average 19 NO eTorque

 

[Electrical]

Psychologically they could be feathering the gas pedal after getting higher octane. Like the person that buys a new $500 pool stick, somehow he shoots better, but it's not the stick, he is just concentrating more for each shot.

I'm keeping an open mind on this topic. I don't believe differences are primarily due to detergents or quality, but rather how the engine map responds to different octane.

We know the map retards timing under certain conditions, like when the knock sensors exceed a threshold, but another way to keep the engine safe is to dump fuel.

If we're talking about running the engine on octane lower than what is spec'd, it's entirely within the realm of possibility to see a richer fuel mixture and maybe lower economy.

 

[SpeedyV]

I'm keeping an open mind on this topic. I don't believe differences are primarily due to detergents or quality, but rather how the engine map responds to different octane.

We know the map retards timing under certain conditions, like when the knock sensors exceed a threshold, but another way to keep the engine safe is to dump fuel.

If we're talking about running the engine on octane lower than what is spec'd, it's entirely within the realm of possibility to see a richer fuel mixture and maybe lower economy.

Agreed and am continuing to test. In various threads, we've also discussed the possibility of build tolerances; some engines come out of the factory a bit 'hotter' than others and will respond to higher octane positively, while it's a complete waste for others. After my first few tankfuls were 93, I've now run a few tanks on 89 (same vendor and same stated ethanol percentage). So far, every tank of 89 has been 1-1.5 mpg lower than 93. It's hard to do a truly neutral test, given changing weather conditions, traffic patterns, and other variables. But I thought I'd benefit from reduced A/C demand over the past month, and I'm not seeing it.

 

[Gman]

Defrost will run the A/C compressor and it really doesn't take that much in the way of horsepower to run a modern A/C compressor these days.

I also have doubts to the Hemi running rich. This would lead to emissions and carbon issues.

 

[Electrical]

...

I also have doubts to the Hemi running rich. This would lead to emissions and carbon issues.

Not "running rich"; "richer mixture". Different.

Fuel dumping is more common in forced injection engines, which is why the Ford Ecoboost gets worse economy under load than a naturally aspirated V8. As far as I know... no emissions or carbon issues.

 

[Gman]

Making power takes fuel. Getting a lot of power from a twin-turbo V6 is possible. More air in the charge also allows more fuel. You also won't get economy out of it under those conditions. The current Ecoboost uses both direct and port fuel injection. I'm not sure what you mean by "forced injection". I have heard of "forced induction", but not "forced injection".

If you're putting more fuel in, then you either have to somehow improve the amount of air in the charge to maintain the air:fuel, or you'll run rich.

 

[Chippy]

I have shell 91 ethanol free here. It seems when I run it I can go longer on a tank. Nothing calculated or logged but the needle seems to hang longer. Conversely my forced induction 6.2 vehicle runs better on 94 with ethanol than this 91.

 

[AnthonyD1978]

I have shell 91 ethanol free here. It seems when I run it I can go longer on a tank. Nothing calculated or logged but the needle seems to hang longer. Conversely my forced induction 6.2 vehicle runs better on 94 with ethanol than this 91.

Ethanol free will get better MPG all things being equal. Also your turbo 6.2 should run better on 94 with ethanol; if by better you mean more power/TQ. As long as your trucks computer is tuned to take advantage of it.

I switched to 87oct from 85oct in my last fill-up from an empty tank. After 20 gallons or so I'm 1 mpg worse than 85oct. I will give it one more tank and if no improvement go back to 85. Or maybe I'll test 91 next. I can't remember the last time I had a vehicle that didn't require 91+ so it's nice to have options.