drew350

Ive owned my RX for just over a year. I have about 14k miles on it. Over the past month or so i have noticed a big decrease in what the cruising range is. I used to get around 312 miles to empty on a full tank. Now im consistently getting 265 miles to empty. Ive used the same gas from the same place and my driving habits have not changed. The basic to and from work and running around town. I use 93 octane always. Ive never used regular. I have noticed that I am filling up the tank more often. I even tried a different gas station thinking i was getting ripped off. Any ideas why this is happening?

ZIN

I think that is question for the dealership or a qualified mechanic.
You seem to have done everything right .

geko29

Check the pressure in your tires. I saw a 17% drop in economy recently in my other car because the tires were low.

mandyfig

Has to be the air pressure.

sama

I also had a drop in my mpg for my 07 RX350 and after the 10K service the Mixed (Hwy & City) Average mpg increased from 21.8 Avg to 23.4 mpg with 89 Octane Fuel.

My TPM light was going on & off by itself prior to the oil change , all is well now.

The toyota dealer found that one tire had 29 PSi instead of 32 PSI.

catdaddylo

Drew, I have had my 2008 RX350 for just a little over a month and if you are referring to your dash computer read out for range in miles after fill up, my readouts (about 4 or 5 so far) have said 267 miles or so. Do a calculation your self on the next fill up. Fill up your tank and set your trip odometer back to zero. At your next fill up, divide the number of miles driven by the gallons of gas to fill the tank back up. This will give you your "real" mpg driving. Since our RX350 gas tank holds 19 gallons you can multiply your mpg X 19 and this will give you the true range of your driving habit range. Let me know after you do this if the 312 or the 265 the most accurate.

By my calculations I have been averaging about 14 mpg X 19 = 266 which is about what my computer said today after I filled up. I would expect that to be more on a trip but I have been driving in stop and go city traffic for the most part of my driving so far.

drew350

Thanks guys. I will check the tire pressure. What psi should i have in there? 32psi? I have the 18" wheels. At what point does the TPM light come on?

Catdaddylo - I will definitely try what you said and let you know.

Grumpa72

THe tire pressure your car needs is on a sticker on the driver's door jamb. Should also be in the owner's manual. While I am a proponent of checking ones tire pressure frequently, I don't think you will see a huge savings or loss with tire pressures. One to slightly more than one mile per gallon might be lost due to a 2-3 pound underinflation, in my experience. Don't forget that cold weather typically causes a lower mileage. Another thing to try is a good fuel cleaner like Chevron Techron available in Advance Auto, Auto Zone and others. I add a fuel cleaner at least twice a year.

As suggested, doing an actual calculation of your mpgs is a far more accurate method of determining your mileage. Anything else is just an estimate.

Gary

lexus114

Yeah,but that is not useable gallons in the tank.Doing the math by 19 gallons would be off slightly,or you would run out of gas.

catdaddylo

If you have 19 gallons in your tank what part of the 19 gallons is not usable ?

ZIN

What he is saying is in order to get an EXACT reading you would have to run out of gas so any gas left in your tank at fill up would be cheating. So to be exact you could run out of gas add 1 gal of gas set odometer to zero then drive around until you run out of gas again and read your mileage. filling your tank and taking it down low would get you a very good idea.

catdaddylo

You do not have to burn up all of the gas in the tank. You start out with a full tank which is approximately 19 gallons. You drive your car until you fill up with gas again. It does not matter if you burned 5 gallons or 15 gallons or 19 gallons. You fill up your tank again and do the math of miles driven divided by the number of gallons of gas used multiplied by 19 and see how close the computer comes to the actual miles calculated by your numbers. Is this as exact as seeing how far you drive until you run out of gas ? No, but you would not be off much where it would make any difference. The point is that Drew was seeing 312 miles and is now seeing 265 miles to empty and wants to know what is wrong. I am trying to show that perhaps nothing is wrong by doing a hand calculation on his driving habits. Perhaps Drew did more city driving, stop and go, short trips than he realized , thus he gets the 265 mile reading where the opposite is true where he got the 312 mile reading.

lexus114

Well,after being a mechanic for a while,I got my cdl,and went over the road,(yes the big sleeper rig)anyway,in those big trucks we had two 250gallon tanks.The problem is it isnt useable gallons.you might only be able to use 210 of that fuel on each side.(due to length of the pick up tube)Now to check fuel mileage,what catdaddylo said applies.Btw,I found I get about 1mpg more than my computer tells me.Witch isnt bad.