Rx Fuel Requirement ?

[fbsdmd]

Just a little anecdotal evidence. I had a 2004 RX330 that was traded with near 80,000 miles on it. Never used anything but regular, never heard any pinging, no complaints about performance, no apparent damage. I now have a 2008 RX 350, only regular gas used in it for about the first 4,000 miles, same as above. I live in the great NE and we now have gasoline with 10% ethanol, all grades, no choice. I recently did two tests, using the MPG calculator on the dash. I realize that this readout may not give an absolutely correct MPG figure, but I think that comparison between MPG readings may be meaningful. The first test was done using regular gas with 10% ethanol and gas without ethanol. Ethanol containing gas was used to fill the tank so that the tank would be near empty after a 150 mile trip. The tank was refilled with gas without ethanol, and the 150 miles was reversed. The MPG readout was carefully observed during the trip, and the maximum MPG for each trip was recorded. I have been told that 10% ethanol will lower gas mileage as much as 2 MPG. Both legs of the trip yielded approx 24 MPG. Now as to test two. I have begun to use high test. Have been using it for the last 4 tank fulls. Today I repeated the same trip as in test one, using high test. Maximum MPG observed was 27.4. I was not able to detect any difference in performance during either test. I realize this is most certainly not an absolutely scientific testing regimen, but there may be a flash of facts here. My first thought is that 10% ethanol, at high, steady speed may not give a noticeable loss of MPG. Secondly, if high test gives a roughly 10% increase in MPG, and the difference between regular and high test is $.20 more than regular, at $3.60 a gallon for regular, you should save money by buying high test. I know, this is a sample of one, but it may have some validity. Thoughts anyone?

Yes... the readout on my wife's IS250 is not accurate all the time. Secondly, in order to do a valid comparison test as you described, and admitted that it wasn't "scientific", it would take more than a single test. There are too many variables that will effect fuel consumption - like: did you use the exact same fuel sample? Was the ambient temperature the same? Was the relative humidy the same? What atmospheric pressure, traffic conditions, wind speed, etc., etc.?

It would be interesting to see some real test data. :D

I would agree about real test data. Almost a year later the issue of regular vs high test is still around. I am over 20,000 miles with the car now, and for the last several months, since the price of gas tanked, have been using regular. There has been no noticeable difference in performance between the two fuels. This Lexus has been trouble free. Did the first two services at the dealer, did the 15,000 at my local mechanic. It would appear that high test may yield about 2 miles more per gallon. Not enough difference to justify high test.