jime

I was too slow to respond to a previous thread and the thread is now closed so I started this new one. I burn premium because it is more economical. The information below came from a 2005 thread when gas was much cheaper. My “rule of thumb” is that the TL gets about 10% poorer gas mileage from regular than premium. So if the price of gas is more that $2.00, it is cheaper to buy premium and at $3.75 (SF bay area) it is a “no brainer”.

jime
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Join Date: Jan 2005
Location: Bay Area, CA
Age: 41
Posts: 1,250
I did the math on this with my car. When I used 87 for a few tanks, my AVG MPG dropped by 2-3 MPG. Here's what I found:

87 octane:
Average MPG: 22 MPG
Cost per gallon: $2.39
Cost per mile: $0.1086

89 octane:
Average MPG: 23 MPG
Cost per gallon: $2.49
Cost per mile: $0.1083

91 octane:
Average MPG: 25 MPG
Cost per gallon: $2.59
Cost per mile: $0.1036

So, it's actually cheaper to run the 91 on a per-mile basis if the engine wants it. If an engine is happy running 87, there is probably no improvement in performance going with the higher octane. The TL's engine is not such an engine with its 11:1 compression ratio.

enigmaos

iTrader: (4)

interesting numbers. premium FTW!

princelybug

iTrader: (16)

I always fill up with premium.

randomhero

Nice breakdown jime. Did you use the same gas station?

MWalsh9152

in my 06 I ran the car both ways, I never heard any detonation. But then I never beat the car either. I always did my comparisons on the highway during long trips with the cruise control set at 65-70ish and no matter what fuel I ran in it it always would average 32 mpg. And I ran a few tanks of each before compairing

Ive never did a comparison with mixed driving though

My Type S has only had premium

phee

iTrader: (5)

i thought the TL retards the timing to compensate for the Gas octane, maybe that is why you still got a consistent mileage...either that or the gas companies are lying

MWalsh9152

Im assuming that it only retards the timing when it senses detonation from the knock sensor, and at highway speed with lower RPMs its not detonating

Jesstzn

Nice break down but like other comparrisons all things aren't equal , only the gallons used per miles traveled.

Variables:
1) Unmatched speeds
2) Traffic conditions
3) Temperature
4) Humidity
5) Barometric pressure.
6) wind ( speed & direction )

All can contribute on any given day to a +/- on any of the octanes.

Something to keep in mind when the difference is so little.

MWalsh9152

very good point

ndabunka

Do'ah - We all already KNOW that man modern cars retard the timing when the octane isn't high enough to warrant the more advanced timing. That is why the premium gets better fuel economy (because the car automatically advances the timing as well). One point many miss is that some older cars do NOT automatically adjust timing and THOSE are the ones where running regular fuel is more efficient. Some newer cars can also advance and reduce timing but since they are lower compression engines, there is no benefit to using premium fuel. An EXCELLENT example is the Lexus GX470. The manual says "using premium fuel may provide better performance" and while it may well be "peppier", the fuel economy actually suffers with premium. SO MANY idiots seem to think that "better performance" equates to "better fuel economy" which simply is not accurate in that case. People interpret (i.e. mis-read) things the way they want too most times.

harddrivin1le

Please provide objective, scientific evidence to support your claim that "the gas companies are lying."

vincethe1

stop "burnin" gas

harddrivin1le

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

Any fuel economy test that was performed in accordance with the scientific method would conclude that any differences in actual fuel economy are next to negligible (e.g. 5% or less between 89 and 91 octane) and that the added cost of premium fuel more than offsets any advantage in fuel economy.

I run 93 octane in mine ('07 Tl-S auto) - mainly to avoid the "pinging" problem that others are receiving. I average 19 MPG in mixed (mostly city) driving, which is 2 MPG less than what I averaged with my LS1 Z28 over the same roads during 6 years and 80K miles worth of driving.

That conclusion isn't in strict accordance with the scientific method, either, though it is based on tens of thousands of miles worth of driving (as opposed to one or two fill-ups of a certain octane fuel).

ggesq

iTrader: (1)

Sorry but this topic has been beaten to death.

If you would like to discuss the scientific method and its outlook on differences in actual fuel economy, please do it in the Off Topic part of the forum. Since we can't move threads there, feel free to restart the discussion. Thanks.