Just completed a 3,000+ mile trip up and down the West Coast and want to share my data. All gasoline was Shell and all reported driving was highway or close to it.

Driving Northbound avg 39.8 (32.8 - 44.5) on regular, 39.1 (35.9 - 45.1) on premium. Total miles 1,881.

Driving Southbound avg 40.2(31.6 - 45.4) on regular, 39.3 (34.4 - 46.5) on premium. Total miles driven 1,912.

All mileage was calculated with my calculator. Per tank numbers varied some what from on-board computer, but not greatly.

FYI - I have a 2010 Sport 5spd and I typically drive 70 - 75. I use dino oil but am planning to switch to synthetic at my next oil change.

Below is a post that I made several months ago that consisted of 1/3 surface street driving at 2/3 freeway (LA ~ 50) and the discussion related to the benefits of using premium if there was any.

2010 Taffeta White




"By the way for those who are following this thread, I have started my own un-scientific test of regular versus premium. I am using Shell regular 87 for the Regular gas and Shell V-Power 91 for the premium part. After 3 tanks of each (I am using the Fit's on-board computer for comparison purposes only and do not claim it as actual mileage). The three tanks of 87 resulted in 38.6 - 38.9. The three tanks of 91 resulted in 37.1 - 37.7. Rightly or wrongly why spend $.20 per gallon more for poorer mileage.


2010 Taffeta White
Sport 5spd

 

Hmm...I'm glad to see some data collected on this.

Very interesting to say the least. Thank you!

 

+rep. Nice. Confirms that there is no need for premium unless you are boosted or the manufacturer calls for it.

 

I am doing the same study right now with my 08 fit on gas as well. But V-Power here is 93 octane not 91 like in Cali. So we will see what i get. As of now on the low grade i was geting 36.7 and 36.5 on the last 2 tanks. And by the end of this i will see what i will get with the V-Power. I also am going to do the same once i change the oil to see if there is any truth in better MPG with different oil

 

Thanks for the thoughts on different octane in V-power. I'll be interested to see if it makes any difference in your test. Somehow I think that the manufacturer would not say that there is no benefit in using premium unless they meant it.

 

The "premium" vs "regular" (unleaded) debate has been going on for some time now and on many forums. The bottom line is that "premium" is really a fuel that is Less volatile, and thus less likely to ignite under higher pressures. That is why they use is in high compression engines, such as anything with forced induction. When you increase pressure, you also increase temperature, and with that you can get the fuel to pre-detonate in those type of engines. So you need a fuel that has a higher ignition point. We are talking milliseconds here but it can make a difference when compared to a normally aspirated engine. If used in a low compression engine, "premium" will actually post detonate, and give you a slower burn, with more unburnt fuel left over to be vented out the exhaust, and with that, less power. Not to say what may happen to your pollution control devices if used over time. You get less power, as you are burning you fuel less efficiently, and thus use more as you go through a tank-full as you numbers would indicate. Bottom line the higher the octane the higher the ignition point of the fuel.

Oil companies love you however if you think the word "premium" makes your car run better. They win on two fronts, one being the price and the second being you burn it faster.

 

I've been waiting for one of these threads, armed with some new info from a book I read recently.

I read a book called "Oil 101" by Morgan Downey. It is a great reference for all things related to oil, but a rather dry read. Anyhow, Octane rating is not correlated with energy content. Some higher rated fuels have lower gallon for gallon energy content.

The main reason higher octane is used is because it can avoid autoignition (aka knocking) at higher compression. Higher octane fuels allow more molecules to be compressed before autoignition would otherwise occur. This allows it to be used in more powerful motors, albeit less efficiently.

 

Although our engine is high compression by traditional standards, >10:1, Honda has designed it to run on low AKI fuel. One way is small bore, long stroke. Another is the centrally-mounted spark plug. Detonation (not preiginition) is caused by radiant heating and the pressure wave from combustion as it sweeps outward from the spark plug to the still unburned mixture near the cylinder wall. The flame front gets there before it can explosively detonate.

 

Premium always give the majority the misconception.

 

If you are planning to compare dino & syn oils in your Fit, I'd like to know what you learn. I am about to do something similar.

 

Ok i will post on here as well if its ok with GW Fit so all this info is in one thread. If not just let me know and i will delete it. But my last 2 tanks with 87 oct was 36.7 and 36.4mpg. With the V-Power 93 oct i got 34.4mpg. So as we all can see does not matter on octane. Cheap gas is better for the Fit. My next test will be synthetic oils and also differnt wieghts. Im going with AMS Oil 10w30 first i still have some laying around the house. Than i will switch to mobile one 10w30 than to mobile one 5w20

 

Syn vs dino - good idea. How about a new thread?

 

We run my bride's turbo Auto Union on premium, and it gets great mileage (30-31 mpg @ 80, trip average), especially for a heavy car with a complex driveline.
Never crossed my mind that premium could have less energy than regular. Makes perfect sense with the explanation.
Moon

 

A higher octane rated fuel is less volatile in the same way that C-4 plastic explosive is to liquid nitroglycerin It is more stable and not as affected by high temperature..... When my car was relatively stock I found that when using regular grade fuel I was getting mileage averages of 33 to 35 mpg at sustained highway speeds of 80 to 90 MPH on regular fuel when I would use it and 37 to 39 with premium.... 87 meets the minimum octane requirements set by Honda for the Fit meaning the ECU will not cut back on the ignition advance for fuel of less octane rating less than 87.... Just get a scangauge and see for yourself.....

 

Just adding. The end gases are cooler and the volumetric efficiency of the motor is higher. So cooler running engine and less gas being use because of higher volumetric efficiencies. check this link it old but the point is prevalent, also keep in mind of our higher compression motors, 2009-2010 has a wide band o2 too. Two-Dollar Vacation Ive seen higher that 10 percent on highway.

 

I think it would be great to post all of you mileage info. From past experience I would suggest multiple tank averages as it is easy to have your Fit sitting at an angle on the pad at the gas station and not get it the same level of "full" on each tank. In my long distance test. I went one step more by making it almost exclusively interstate driving and including both northbound and southbound mileage calculations.

I'm really interested in seeing the results on synthetic oil. This is the only step I have not tried.

 

I can account for every drop of gas burned in 12k miles; 56 fillups, less than 1% under an indicated 30 mpg. All of it was regular, most of it consumed intown or on short trips, and I changed to synthetic (5w-20 Castrol Syntech) at 7200 miles. A quick perusal of the numbers doesn't seem to indicate any improvement at that mileage. Do we know what Honda puts in the sump at the factory? Hard to believe that it isn't synthetic, considering the extended oil changes that the computer calls for.
Agreed that the onboard computer is better for comparing relative mileage, even allowing that it is a little optomistic; it's still more accurate than just measuring fillups. A buddy did a big fillup followed by a short one, and will swear on a bible factory that his VW Rabbit got 45 mpg...
Also, the onboard computer in the Auto Union (which seems very accurate, BTW) computes average speed on a tankful; I've been keeping track of that as well. Not surprisingly, high average speed also correlates as high average mileage. That doesn't mean that going really fast is the best way to get good mileage; it just winnows out the short-trip tankfuls compared to the travel ones.
Mighty happy with the Honda's mileage (actually, with the Audi's as well); gotta get to the dealer one of these days and maybe get the computer corrected...
Moon

 

Great info keep it coming.

I have changed oil twice on my '10 at the dealer and will be switching to Castrol Syntec 5w-20 on my next change in my garage. Further I'll switch filters from Honda's "Blue Can" by Fram to a Pure One. Unless the Fit is different from my last 3 vehicles (2 Toyota's and a Nissan), the syn should increase my highway mileage by 1-2 mpg. At least I hope it will.

 

I wouldn't bet the farm on that. I've gone to 6k changes and synthetic for everything in the house, and haven't seen any noticeable change in mileage. The longer change period is just less trouble and ultimately less expense, if I can get past the guilt factor...when I was a young driver, my buddy's dad, a major gearhead, counseled changing the oil evey 1K, and I did...
Moon

 

This kind of makes you wonder whether Honda puts synthetic in as a break-in oil. If you go to a dealer after that and they put in dino oil that you don't notice the difference as everything is starting to loosen up and give you better mileage. As all of my mileage tests have been in between oil changes, I'll do my change over with a test just before and maybe 100 miles after. Don't know any other way to check this.

The one thing I have heard is that you should not put synthetic in until your rings have thoroughly seated. Don't some manufacturers put in synthetic at the factory? Hmm, makes you wonder.