YWW

I have a 2008 RX350AWD that I purchased new in March currently has 5800 miles. 2 of my friends also bought same model around same time currently with similar miles. We all use our RX primarily in city driving with occasional highway. My RX mileage computer had been registering around 18.2 to 19.1mpg for my typical driving since March and my friends' RX also averaged right around 17.8 to 18.6. Well, as of October, my mileage went down to 15.6 to 16.8 during the last 4 fillups. I didn't change my driving habits nor routes. My friends' RX also experienced a sharp drop in mpg around same time. In fact all of us use Shell premium gas so that ruled out some off brand gas causing problems. My RX drives fine as always. Do any of you know why we are seeing this gas mileage drop? My friends were guessing it might've something to do with the winter blend gas they sell in the Midwest vs the summer blend we were using previously. I find it hard to believe a different blend can cause such a drop in mpg. Do any of you know why this sudden drop in mpg?

jgr7

iTrader: (1)

The winter blend could be doing that, it most likely has ethanol which burns with less BTUs thus giving you less MPG.
Jeff

sup_lexio

the computer calculate your mileage according to the mileage used by the car ((this is read by flow ((sensor)) reads the how much gas is going to your injenctors. now a new tank the system Estimate the mileage and gas you used in your previous tank and give you those number thats your drop divided in mpg . not the new filled tank. what the computer is telling you.. For example if you take I95 from NY to atlanta your next tank is going to reflect 318mpg a full tank and maybe 23mpg even more on average but you stay a week of local driving it will go back maybe even 13 gpm it varies if your driving most local or both highway also you will have a low gpm reading for the simple fact that you wasn't doing 80mph for a long distance . it has nothing to do with premium or regular even winter blend. my suggestion keep using(( premium)) prevents knocking and just check what im telling you. good luck

grouch

I agree with "jgr7". We have the same thing in Montana. Read the pump. It should state if it's a blend and what the percentage is.

YWW

sup_lexio, are you saying the computer mpg reading is not the current mileage average but rather the average of the previous tank? When you fill up, the computer resets to zero and starts that calculation. In my case, the mpg I provided in my original posting is not the initial mpg immediately after the fillup but rather over a week to two weeks later before the next fillup. Besides my routes and driving habits didn't change nor did my friends' 2 RXs.

I checked on the Shell pump and it does say 10% ethanol added which I never noticed before. It translates to a 15% or more drop in my gas mileage with this additive if this ethanol is the culprit. If this ethanol is so inefficient, why would the oil company even add this into their gas? Seems like the wrong thing to do if we are to conserve energy.

grouch

I believe it's part of the "clean air" act. You sacrifice mileage and cash for cleaner air.

jgr7

iTrader: (1)

The problem with there (the EPA) thought process is that you burn more fuel to go the same distance with the ethanol additive so you put more pollutants in the air because of the loss of MPG. The fuel we burn with out the ethanol falls well within the pollution standards. This is just another failed government mandate that did nothing but raise the price of corn and cause shortages of corn for feed. It also gave subsidies to corn farmers so that many farmers switched to corn where they could and this caused shortages in the crops that they used to grow.
Jeff

CTtech

I also have an 08 RX350 and have seen similar resultsa under identical conditions. From my research I have found a couple of things could be attributing to our lower MPG's. One, as mentioned, is the winter blend of gas and another is the cold weather. This time of year it takes your vehicle longer to come up to an efficient running temp therefore your vehicle is less efficient initially each time you turn it on after sitting. I have come to accept this as normal. Enjoy your RX and the currently lower gas prices. You will see your initial MPG results again in the spring.
Just my 2 cents,

Boognish

"Winter" gas is oxygenated to reduce CO emissions. Alcohol is the preferred oxygenating agent, although MTBE was used for a while here in CA. The MTBE was kind of a "whoopsie" because it is a very small molecule capable of permeating rocks and getting into aquifers used for drinking water.

http://www.epa.gov/otaq/oxygenate.htm

Oh, and corn ethanol is just a scam to subsidize farmers...