waymay1305

I've noticed that the MPG averages around 19.4 but the tank average is usually higher which is about 23.4. What's the difference? So, with my combined city and highway driving which one should I be concerned with? Of course, I want the highest MPG.

LexBob2

The MPG average is the cumulative total since the function was last reset. The tank average is since the last fill up. The tank average resets each time you fill up or add gas.

dreyfus

LexBob2 is correct about what the the two MPG readings mean. But what you want isn't the highest MPG, you want the true MPG.

To figure out the actual MPG of your car fill the tank up to the top and record your odometer reading (or reset one of the trip odometers). When the tank is nearly empty, refill to the same level and record the number of gallons used (this won't be exact but it will be close enough). Take the current odometer reading and subtract the earlier one to get the number of miles driven (or read directly from your trip odometer) and divide this number by the number of gallons used to get your actual MPG.

I (and others here) have found that the car's calculation of MPG is optimistic by about 1.5 to 2 MPG. Since no one has yet said their car gets better gas mileage than the display readings I suspect this isn't random error but rather is intentional on the part of Lexus to give the appearance of better MPG than the car actually gets.

jagtoes

waymay I guess I would not be happy with your results. I just returned from a weekend trip where I put 475 miles on the car. I still have not filled the tank but my tank MPG was 30.6 . This was at highway speeds (80MPG ) mixed with about 60 miles of city driving. I usually get a combined avg of 27 mpg and 23 mpg city. In the past when I have done an actual calulated mpg it pretty much is the same as what's on the instrumentation.

codex57

My other car is a Honda truck. It gets 21-22 mpg on the highway. So even if it's optimistic by 2 mpg, I've gotten the Lexus to show 33 and 34 mpg quite a number of times. If this thing is getting 30+ on the highway, I'm thrilled. 3.5L engine with all that power? My old BMW with a dinky 2.5L didn't get as good mileage.

toneman

I did a simple test using the cruise control to see what kind of (indicated) fuel economy the ES gets at certain cruising speeds (65 and 70 mph)--what I did was to find a relatively flat road (i.e., no rises/dips/hills), set the CC at the desired speed, then--while vehicle is still in motion--reset the overall fuel economy reading so that the computer would be computing the mpg based on a fixed (i.e., speed did not vary at all during the test) speed. This eliminates any variance in mpg that would result from varying the speed--i.e., the mpg readout won't be affected by changes in speed.

I ran a few tests at both 65 and 70 mph--at 65 mph my ES was reporting anywhere between 35-37 mpg; at 70 mph it was anywhere between 33-35 mpg. Test was done using regular unleaded gas, and I was the only occupant in the vehicle; I would guess that using premium would return an extra 0.5 mpg or even 1 mpg on top of those figures. It goes without saying that other factors could affect the results--e.g., wind, drafting, ambient temperature, tire pressure, weight--but AFAICT there was very little wind during the test, and I ran the test during the morning hours (outside temp 55 degrees F).