I find it interesting that I can go 300 miles on city streets and average maybe 17mpg, but then maybe 20 miles at freeway speeds will kick the average up to 19 or more.

Just today, my average was sitting at 16.9, with about a half-tank of gas burned. After maybe a twenty minute jaunt on the freeway at 70mph, the "average since last fillup" display jumped to 19.1.

I've noticed that at 70mph, the tach is sitting at 1700 rpm, whereas at 35mph it's at maybe 1100. That means the engine is turning only about 50% faster at 70, but the car is covering twice as many miles during any given time period. That certainly accounts for the better mileage, but I just find it interesting the overall average can be pulled up so much in so few freeway miles!

Guess I'll have to make a 20-minute freeway run on each tank to keep my overall gas mileage up!

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It is interesting but it does make sense. In that 20 miles of highway driving at 70mph you are probably averaging 27 mpg. I find that if I am careful and drive as if I am driving a hybrid vehicle, I can average 19 in city driving. This means you need to anticipate stops and do some coasting and you do not have very rapid accelerations. That really eats up gas. On the Interstate, I am averaging about 26 depending on outside air temperature and wind conditions. I live in the Midwest where, as you know, the winters are cold. You do not get as good gas mileage in cold weather. The colder it is the worse your gas mileage will be. I expect that once temperatures warm to at least the 50s and 60s (Spring), my highway gas mileage will jump to 28 mpg.

BTW, I had an earlier post where I stated that I am now using 10% ethanol with 89 octane instead of premium and 91 octane. I have not noticed any difference at all in the gas mileage nor have I detected any drop in vehicle performance. This is good news for me since in my state, 10% ethanol is 30 cents per gallon cheaper than premium. It is about 13 cents cheaper than even regular unleaded with 87 octane. Maybe you should all move to my state ;-).

 

don't forget it's mainly about how much gas you need to keep it at that speed / rpm.

ls460 travels at 80mph at 2k rpm. with mixed driving, i got around 22mpg constantly when it was stock. now with 22s, they are heavier. i still go at around 80mph (rpm still 2k) most of the time, but gas mileage dropped to 20.5-21mpg (constantly).

 

If you want more accurate performance readings, make sure you reset all your readings to zero - not all of them can be reset mind you, but that should set new benchmarks to compare the "average since last fillup" readings to.

 

Maybe you should all move to my state ;-).

Move to Illinois, or whatever Godforesaken state you're in, to save a lousy 13 cents on gas?! I don't think so!

 

Right, Burnaby. I always set everything back to zero at every fill-up, but of course the LS automatically calculates mpg "since last fill-up".

I've always been amused at those people who say their mileage never seems to vary much no matter what they do ... only to find out, duh, you have to reset the tripmeter to get a current average.

And PatSoxfan - we get 10% ethanol added to all our gas here (since the EPA has decided we make too much pollution ), but I still use the 91 octane stuff.
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Mike, let me get this straight. If I understand you, in your state, all grades of gasoline have 10% ethanol, right? That's not the case here. We have 3 options here: 1)regular unleaded, 87 octnane and no ethanol; 2)10% ethanol at 89 octance; 3)premium unleaded at 91 octane and no ethanol added. The 91 octane (no ethanol) costs about 30 cents more than the 89 octane with 10% ethanol. The regular unleaded (no ethanol) at 87 octane costs about 13 cents more than the 89 octane with 10% ethanol. Thus, I have been using the 89 octane with 10% ethanol recently. I don't see why not.

 

Well, it's a little more complicated than that.

Cities the EPA has ruled to not be in compliance with pollution standards are required to use something they call "oxygenated" fuels. They achieve this several ways, but as I understand it, adding up to 10 ethanol is one of them.

So, the pumps in the Dallas/Ft. Worth area, for example, have a sticker that warns that the fuel may contain up to 10% ethanol (which is the maximum allowed here), All grades - regular, mid-grade and premium - have it added.

Now, I think there are some brands of gasoline that achieve the oxygenation requirement differently, and don't have the ethanol, but most do.

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That is very interesting and wierd I might add.

 

So what octane are you guys filling up with? I just filled up my tank since I took delivery few weeks ago and I am using premium (93 octane). It states to use premuim so that's what I am using? Are you guys saying that the LS will run well on a lower octane(91octane)?

 

My mileage is very different for city vs. freeway (460L exec) I get about 16 mpg for city and 25-28 for freeway (70-75 mph). This is more extreme than my old LS400 (1991) which was still getting about 20 mpg at over 300K miles. I did drive much more freeway miles with the 400 (before I retired!). I believe the 460L gets better freeway mileage, even though it is a bigger and heavier car than my old 400. I think that is reflected by the new 2008 EPA city and highway numbers. The 600 should be closer to the same for city and highway, since it should use the electric motor more for the slower driving. The Prius actually gets better city mileage than highway.

 

91 octane is actually what is usually referred to as "premium" gasoline. In fact, it is the highest octane we can get here in Texas AFAIK. In other states, it goes as high as your 93, but I might add lots of gas in Texas that's labeled as premium is only 90 octane.

So, yes, 91 octane is fine.

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yup, i believe the 8 gear is what help the most. on the ls400/430, at 80mph, you are at around 3000 rpm. with the ls460, it drops right down to 2000

 

As I stated above, I started out with 91 octane (maximum octane here with no ethanol). However, I have switched to 89 octane with 10% ethanol. I do not notice any difference in gas mileage or performance. The manual says they recommend 91 octane but it does not say you cannot use 89 octane. It will not damage your engine or anything like that. Most think that a lower octane than 91 will result in lower gas mileage and worse performance. I do not see the logic in using 91 octane and 30 cents per gallon more expensive than the 89 octane (10% ethanol) since my car runs just fine with the 89 octane.

 

Pats - Regardless whether the gasoline has some ethanol in it or not, it's still 89 octane. IOW, ethanol octane isn't any different than gasoline octane ... it's all a measure of how well the substance burns (or resists detonation).

Your car has a knock sensor that detects detonation when you use fuel that is lower than that which the engine is designed to run on, and it responds by retarding the timing to protect the engine. You probably can't detect it, but it does reduce engine power a bit, since the engine is no longer operating at the optimal spark advance setting. Over time, it probably contributes to a buildup of carbon in the combustion chamber and on the valves and rings.

Having said that, 2 octane points is probably not enough to lay awake worrying about, but I personally wouldn't do it. The message is right there inside the filler door every time you fill up: "Use Premium Unleaded Fuel Only".

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