Use of mid range gas to get better mpg

I used one tank of a mid-range gasoline during an 800-mile round trip I've taken on at least five occasions with my 2007. The mid-range tank had significantly lower (10% to 15% lower) gas mileage (51.3 v. the prior two of 56.7 and 60.4 and the following one of 59.0).

 

higher octane gas only means that it has a higher flash point. higher flash points prevent pre-ignition in high compression engines. as the gas is compressed, it heats up. heat up too much and it might get hot enough to ignite on its own too soon. this is what causes ping.

ping is just a mini explosion that happens too early and that basically reduces the explosion that spark plug creates because part of the fuel has already been burnt off before the ideal crankshaft position has been achieved.


imagine driving rolling hills, you go down a hill, build up speed, go up the next hill crest it and go back down again now what if you could only accelerate for say 4 seconds. when is best time to do this? ...pinging is accelerating just before you hit the top of the hill. at this point you are going slower and acceleration may only increase your speed a few miles per hour. you crest the hill at a much slower speed, so the downslope does not generate as high a speed at the bottom of the hill causing a huge loss of speed. now if you were to accelerate after you crest the hill, you are starting your acceleration at a higher speed and you also have gravity on your side which allows you to increase your speed by several mph.

also, as has been stated, higher octane gas has less energy in it. its full benefits are not realized unless the compression ratio is high enough which in itself will create more torque in the engine because of the percentage increase in the chamber volume as the piston is pushed out.

in a low compression engine, you want to get the octane as low as possible because the actual power output is higher. if you want better gas mileage, try 85 octane (if you can find it. usually only will see it at higher altitudes)

 

I've read numerous articles on using higher octane gas in vehicles that don't require it. The articles always say that using the higher octane is a waste of money and will not benefit you. But, after using higher octane on a Chevy Astro, and two Toyota truck's, I've found that they actually do get about .5-1mpg more. Not worth it IMO, but it did net higher MPG's...

I will be using only 87octane in my Prius. Gas here is at $3.20/gal for the 87 right now...

 

your results may have been realized because of the addition of a premium cleaner that most service stations add to only the Premium grade

 

You guys think so? I was wondering why my results contradicted all the articles I have read...

 

Only if your you do not normally use a major brand (Mobil, Chevron, etc.) which have additives in all grades.

 

Is Fred's Discount Gas and Heating Fuel a major brand?

Tom

 

I'd like to suggest an approach, a methodology, that you can use to perform your own gasoline studies.

REQUIREMENTS

• Reset-able, trip meter and mileage display - something you can use to record what happens climbing from the bottom to the top of a significant hill, say 500 ft, at high speed, say +50 mph.
• Hill climb road with periods of low traffic - this may mean early morning or late night runs to avoid traffic that might block climbing the hill at the target speed

METHODOLOGY

1. Know what fuel is in the tank. This can be done by running it very low and doing a couple of fill-ups with the test brand. In the past with my NHW11 Prius, I run it until the engine stops and the proceed in EV mode to a safe place to add 1 gallon of the test gasoline. DO NOT DO THIS WITH YOUR ZVW20 ... IT GIVES NO CHECK ENGINE LIGHT OR OTHER INDICATION THAT THE ENGINE HAS ACTUALLY RUN OUT OF FUEL!
2. Warm up the car at whatever speed you'll be climbing the hill. I recommend it be at least 50 mph and higher if safe.
3. Approach hill and set the cruise control, trim to make sure the speed is steady.
4. Reset the trip meter and MPG gauge at the "entry" point to the hill and drive safely to the crest.
5. At the same "exit" point, note the trip meter miles and MPG. As a safe place or using an audio recorder, save these values.
6. For better accuracy, re-run test.
7. Optional, re-run tests at different speeds:

Plot the results and share them with the community.

Bob Wilson

 

Bob, is there a situation you don't have a graph for? I salute your efforts to help us all out. :rockon:

 

Bob Wilson

 

Why does the manual (p. 560) say to use 88 octane or higher, then go on to suggest anything lower may cause pinging problems? If I'm understanding you all correctly, 87 is the way to go, yet clearly that is below the manufacturer's recommendation. Thoughts?

 

My fuel studies with the 1.6L engine suggested that at very high power levels (aka., high speed, hill climbs,) a higher octane fuel will let the engine tune itself to achieve nearly the same efficiency as E87. I'm seeing a similar effect between the E89 the dealer put in the tank and E87 in my most recent hill climb data.

If I had regular, high-speed commutes in mountainous states like West Virginia or western North Carolina, I would consider running a higher test gasoline. However, I would want to do a couple of tanks both ways and see what happens.

Bob Wilson

 

Bob, i appreciate the suggestion to use 89 or better while mountain climbing. we have a trip scheduled to western NC in a couple of weeks. i be running 89 for the trip. since its summer time (higher temps) would you suggest premium (91/93) over 89?

 

With mountain driving, if you are talking about high altitude, the required octane goes down. In many western areas standard octane is 85. Lower air density calls for lower octane.

Tom

 

I don't have any 91/93 data that shows the engine tunes to use it. Understand there are narrow power bands, primarily going up a grade at high speed and needing to accelerate that the higher octane can help. This is a very small percentage of ordinary mountain driving ... important sometimes but still pretty small.

I'll still run 87 octane and 'I follow trucks' by letting them set the climbing pace. It has more to do with 'me be cheap' versus being in a car with impatient people who are anxious to find the next bathroom. <wink>

Also, I have long wanted to get some 85 octane gas for my studies. Sad to say, we're only around 700 ft. so 87 is the lowest we get.

Bob Wilson

 

fair enough, thanks to both for the replies.

 

The owner's manual has been revised since then - 87 octane is correct. Do a search for "88 Octane" in the main 2010 Forum - there's a nice long thread about it. __________________
If the owner's manual has been revised since then, why is it in the new cars? I just got mine last week and must have the "older" manual. Strange. How does one keep abreast of all the changes?