Mileage and Octane

[bobt]

I drive 750+ miles per week so I’m very concerned about gas mileage. My local station sells 87, 89, and 93 octanes. So the recent spike in gas prices caused me to start using 89 octane. BTW - your new ’04 TL runs just fine on 89 octane with no knock or problem at all. I have been tracking mileage and comparing the MID average with actuals for several weeks now while using both 89 and 93 octane. Here are the results. And remember, these come from the same gas station with the tank filled to the same level and, usually, with the same pump (if I could get to it). All comparisons ran for about 2 weeks (1,500 miles) each. My TL now has approx 21,000 miles on it. I use 0W-20 Mobil-1 oil and the tires are inflated to 34 PSI. I drive a toll way into the western suburbs of Chicago so my speeds range from a cruise of 50+ miles at 75 MPH to 20+ miles at 30 MPH down to stop and go traffic. A pretty good mix of driving conditions. While using 89 octane I averaged 26.6 MPG While using 93 octane I averaged 28.8 MPG. Over the course of a week, 750 miles, I burned approx. 28.2 gallons of 89 octane at a cost of about $53.30 (at $1.89/gallon). Using the 93 octane, I burned about 26 gallons at a cost of almost $51.74 (at $1.99/gallon). Over the course of a year, about 37,500 miles, you would save about 107 gallons using the higher octane. This saves you $213/year buying the higher octane gas. If I remember correctly, RoadRage did a similar study a while back. He’s made me a believer now.

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[SouthernBoy]

I'm not at all surprised with your results as I've seen similar results when just the opposite situation exists; that is, using higher octane fuel than an engine is designed to use with no added-on mods to take advantage of such.

Basically, your timing was retarded by the ECU which means that the spark occurs higher up in the compression stroke. This results in less fuel burned before the exhaust valve is opened to begin cylinder purging. It also means that a slight increase in throttle would be required to attain and maintain a given speed which also results in more fuel burned.

Good test and good for you!

[Jinen]

Umm...interesting...I always fill up the highest ocatane available...I believe the one, here in Arizona, is 91...I always felt that it would be better for the car overall, but did not think it would effect mileage... ....Thanks for the info!!!

[Repecat]

Bobt....Thanks for another piece of confirming evidence. Good job and deserving of points.

[Ron A]

bobt: From one who has been saying this for a long time, here's a big

hi rets and whoever else is looking..............and one more for good luck

[GUMP]

Great post...thanks for the info..

[Tommy]

Now I can happily fill up with Premium knowing I will save money.

[ResearchFreak]

Thanks for the information! Points for you!

[Acuraluvr]

wow, everyone tells my that get cheaper fuel..... thanx for the post!!! points acoming!!!

[ayethetiense]

uhm, 91 octane here is 2.40 if you're lucky =) imagine my joy!

[UnsanePyro]

This may sound like a question, but I've always sort of wondered about accelerating. I know thats when you use the bulk of your gas, holding the car at 80mph doesn't take much, but getting there does. Now to get there, would it make sense to accelerate to the peak of the engines power, so you get the most efficiancy from the gas? Or is this just a thought... (I'm only 17)

[SouthernBoy]

To UnsanePyro;

No it wouldn't.. and a good question, by the way. Street tuned engines generally deliver their best efficiency somewhere between 2000 and 2500 RPM. This is due to the fact that at these engine speeds and with our TL engine, available torque is in the vicinity of 90% of its maximum rating and the engine is well beyond any primary metering speeds (circuit).

If you took the engine up to 6700 RPM in first and second gear on your way to 80 MPH, you would not only be burning quite a bit more fuel, but you would be stressing your engine more than necessary and too often.

The engine will easily spin to 7 grand, but you don't want to do this on a regular basis.

Hope this helps and don't start any fires, Pyro.

[producrdel]

I use 93 Octane and generally get around 22 MPG with local driving, not bad at all.

[RJANACONDA]

i used to not think that brand of gas made a differance mine use to "ride funny" according to my wife (i was deployed at the time) we were useing BJ's gas if you don't know what that is is it like Sam's club and then she switched to useing BP and the problem went away and never came back

[TheChamp531]

Originally Posted by bobt

I drive 750+ miles per week so I’m very concerned about gas mileage. My local station sells 87, 89, and 93 octanes. So the recent spike in gas prices caused me to start using 89 octane. BTW - your new ’04 TL runs just fine on 89 octane with no knock or problem at all.

I have been tracking mileage and comparing the MID average with actuals for several weeks now while using both 89 and 93 octane. Here are the results. And remember, these come from the same gas station with the tank filled to the same level and, usually, with the same pump (if I could get to it). All comparisons ran for about 2 weeks (1,500 miles) each. My TL now has approx 21,000 miles on it. I use 0W-20 Mobil-1 oil and the tires are inflated to 34 PSI. I drive a toll way into the western suburbs of Chicago so my speeds range from a cruise of 50+ miles at 75 MPH to 20+ miles at 30 MPH down to stop and go traffic. A pretty good mix of driving conditions.

While using 89 octane I averaged 26.6 MPG
While using 93 octane I averaged 28.8 MPG.

Over the course of a week, 750 miles, I burned approx. 28.2 gallons of 89 octane at a cost of about $53.30 (at $1.89/gallon).

Using the 93 octane, I burned about 26 gallons at a cost of almost $51.74 (at $1.99/gallon).

Over the course of a year, about 37,500 miles, you would save about 107 gallons using the higher octane. This saves you $213/year buying the higher octane gas.

If I remember correctly, RoadRage did a similar study a while back. He’s made me a believer now.

----

[lusid]

lol? 4year necro bump!

[YeuEmMaiMai]

it's abvoius with the results on an engine that is tuned for higher octane.

but people don't see it that way........

I have never run anything lower than 91 octane and I get pretty good mialge in the CLS

[SouthernBoy]

This does not surprise me at all. However, I would have been surprise if you had reported results just the opposite of what you experienced. The reason for this difference is in the ability of the engine and its management system to extract (produce) power from a given amount of fuel/air mix during each cylinder fill. Burning a lower grade of fuel will force your ECU to retard ignition timing a little and alter the fuel/mix slightly to compensate. Now we have the engine producing a little less power which equates to the driver having to tip into the throttle a little more to attain a desired rate of acceleration and speed.

I did something like this in reverse 14 years ago. I had a Honda Accord EX 5MT which required 87 octane fuel. I filled the tank with 93 before heading out on a vacation road trip. I recorded not only less economy, but a distinct drop in usable power. I knew this would be the results, but I just wanted to prove it.

[YeuEmMaiMai]

car and driver did it with a V6 J30a accord and got the same results

slower accelleration
less power

[juruki]

those good old days, when gas used to cost 1.80 sigh
20 bucks for a full tank i miss you!!!

[TLTrance]

Having sub $3 gas makes me happy...

[lusid]

1.96 in MN as of today!

[Hpdrifter]

I have been tracking my milage since I bought my TL. I write it down in a book I carry in the car. After reading several articles, including ones in Car and Driver I decided to put the Octane claim to test. Although I'm not sitting with my milage book in hand (I can post the actual numbers if needed) I can say that I came to the same conclusion that Car and Driver did. I see no difference what so ever in milage based upon octane. I have run 87, 89 and 91. I average about 23-26 MPG on each tank of gas. I generally get just over 300 miles per tankful. I drive at least 22k per year. I can tell you that I generally run 87 or 89. I tend to alternate tankfuls. I have been told that the biggest difference between 87 and 89 is that the lower grade doesn't contain the detergents that help clean the injectors. (That's why I switch back and forth). I'm going to try and post the info about the Car and Driver article because they came to the same conclusion. Higher Octane doesn't mean higher milage.

[vinnier6]

i can tell you for a fact that my type s gets better milage with 93 vrs 89, and its a big enough difference that it cost me more money to use the 89 octane...

i dont believe you or car and driver for that matter....

simple math for me, a tank of 89 gets me 300 miles, and a tank of 93 gets me 350, simple as that....one octane gets me about 23mpg, and the other gets me about 26....your car, your money, do what you want, but dont tell me about facts, i can do math....

[I hate cars]

I've been preaching this for a while now that it's cheaper to run premium in the TL.

I'm sure other cars with lower compression or less aggressive management could get by with less octane with no mpg or power hit but the TL needs it.

Keep in mind retarding the timing makes EGTs go higher so not only are you losing power and economy but you're heating everything up from the exhaust valves on. It might not be enough to hurt anything but it's still happening.

[SouthernBoy]

Originally Posted by Hpdrifter

I have been tracking my milage since I bought my TL. I write it down in a book I carry in the car. After reading several articles, including ones in Car and Driver I decided to put the Octane claim to test. Although I'm not sitting with my milage book in hand (I can post the actual numbers if needed) I can say that I came to the same conclusion that Car and Driver did. I see no difference what so ever in milage based upon octane. I have run 87, 89 and 91. I average about 23-26 MPG on each tank of gas. I generally get just over 300 miles per tankful. I drive at least 22k per year. I can tell you that I generally run 87 or 89. I tend to alternate tankfuls. I have been told that the biggest difference between 87 and 89 is that the lower grade doesn't contain the detergents that help clean the injectors. (That's why I switch back and forth). I'm going to try and post the info about the Car and Driver article because they came to the same conclusion. Higher Octane doesn't mean higher milage.

This is a very generalized statement in that higher octane burned in an engine not designed for it will produce less power and lower fuel economy. Higher octane used in an engine that is designed for it will allow the engine to produce the power and economy for which it was designed. Using a lower grade of fuel will have negative results of which I spoke in a prior response.

As for your statement, "I have been told that the biggest difference between 87 and 89 is that the lower grade doesn't contain the detergents that help clean the injectors", I have to tell you that whoever told you this misinformed you. All gasoline grades sold in this country since 1995 are required to contain detergent additives as mandated by the EPA.

[SouthernBoy]

As a follow-up for those who seem to have difficulty understanding the concept of octane, what it is, how it "works", and the why of it all, here is a link to a good start.

http://en.wikipedia.org/wiki/Octane_rating

In the simplest manner possible, octane is a measure of a fuel's resistance to detonation in a gasoline engine. Gasoline engines burn a fuel/air mixture.. they do not induce an explosion - at least not deliberately. Factors which affect this are the mechanical compression ratio, ignition timing, load, altitude, temperature, and the general condition of the engine and its components.

One of the biggest fallacies is the idea that burning 93 octane fuel in an engine designed for 87 will produce more power and result in increased fuel economy. If nothing else, common sense dictates this to be completely false. Such and engine will not be able to utilize the fuel to its maximum advantage because it will not be able to create as an efficient burn as with the lower grade of fuel. Also, higher levels of carbon will be deposited on the piston tops and valve faces. This will raise the compression ratio some, but not in the manner in which you would want.

The reverse is true for an engine designed for premium fuel, but worse since the potential for damage exists.

Gentlemen, read the link and do some research before you believe an old wife's tale or are sold a bill of goods.

[liquid-s]

I am getting around 310 to 320 for 14 gallons which is tankfull for my 2008 TL-S, is that normal?, i use 91 octane.

[TLAdvanced]

Originally Posted by liquid-s

I am getting around 310 to 320 for 14 gallons which is tankfull for my 2008 TL-S, is that normal?, i use 91 octane.

When you say a tankfull do you mean 14 gallons or 17 the tank really holds? If 14 that sounds about right...

[liquid-s]

yes its for 14 gallons, i did not know it could hold 17 gallons

[Wish I Had A TL]

Originally Posted by liquid-s

yes its for 14 gallons, i did not know it could hold 17 gallons

Yeah, 3 gallon reserve.

[hirsch014]

Just read the gas door. cars will either say premium fuel ONLY, or premium fuel RECOMMENDED. most people dont notice the difference, but its significant. From looking through the acura site, looks like every car of theirs requires premium (min 91), except the TSX, where its only recommended, but is also designed to run on the 87 without issues. (this is for the newest models, i dont know about the earlier ones).

For all BUT the TSX, they even state "Using gasoline with an octane lower than 91 octane may cause damage to the engine." for the TSX, they say "Gasoline with an octane number lower than 91 may be used, with reduced performance. Use of a gasoline with a pump octane number less than 87 can lead to engine damage."

i understand the lack of trust in dealerships, but not sure why people keep trying to ignore the designers of the car. they obviously know what theyre doing if they can build a car like this. and if you want it run as long as possible, give the engine whats it's designed for. i just dont get it.

[Majofo]

Originally Posted by hirsch014

Just read the gas door. cars will either say premium fuel ONLY, or premium fuel RECOMMENDED. most people dont notice the difference, but its significant. From looking through the acura site, looks like every car of theirs requires premium (min 91), except the TSX, where its only recommended, but is also designed to run on the 87 without issues. (this is for the newest models, i dont know about the earlier ones).

For all BUT the TSX, they even state "Using gasoline with an octane lower than 91 octane may cause damage to the engine." for the TSX, they say "Gasoline with an octane number lower than 91 may be used, with reduced performance. Use of a gasoline with a pump octane number less than 87 can lead to engine damage."

i understand the lack of trust in dealerships, but not sure why people keep trying to ignore the designers of the car. they obviously know what theyre doing if they can build a car like this. and if you want it run as long as possible, give the engine whats it's designed for. i just dont get it.

huh? you know this is a revived thread right? but yes.. there's still those out there who think their 11:1 CR engine can handle 87 octane with no issue.

Although this is a revived thread the matter of fact is that running on anything less than 91 is senseless since a few cents saving at the pump pretty much evens out in fuel efficiency and engine maintenance.. until knock starts to occur.. then you're fkd.