Maybe someone out there can help me diagnose a problem I've been having with my Lexus. Over the past year, I've witnessed my gas mileage decrease steadily from about 325 miles per tank to about 235-250 miles per tank. I've taken the car to a Lexus service center, and they can't find anything wrong with the usual suspects (spark plugs, air filter, tire pressure, catalytic converter, what have you.) Furthermore, they did a mileage test and said they were averaging 20 mpg whereas the best we can get is about 13. I asked them to empty the tank and drive through a full tank of gas -- they reported back that they got 351 miles, on a combination of highways and surface streets, and suggested the problem was the method in which we're driving. I don't know what to say except we're not at all lead-foots. I kept talking to the service tech, and we got to talking about what kind of gas we're using. My wife and I almost ALWAYS fill up at the same station (Shell), which he said could be a signifier that we're simply buying bad gas. Furthermore, we incorrectly had been assuming that the car required premium gasoline, whereas it's actually balanced for regular. He said that putting too high of an octane will cause the car to not burn the fuel properly and that we could have been leaking unburnt fuel out of our tail pipe.

I'm a little skeptical about all this -- I'm skeptical that we drive this thing so horrifically that we can be getting such vastly different mileage than the service techs. I'm skeptical that too high of a gas octane can result in such a dramatic drop in fuel efficiency. I suppose we could just be getting bad gas, but... there's gotta be something else going on, right?

Anyone else run into this problem? Any ideas?

Thanks!

 

Why don't you start by describing how you typically drive your car in great details to see if we could offer any clue to your low mileage issue ...

 

Whoever told you using too high an octane will cause problems is an idiot.

Did the dealer suggest putting a data logger in the thing to record what everything is doing?

I use this one:
It pretty much records everything that is going on so it would eliminate driving style and possibly point to some sensor.

 

You are NOT getting bad gas consistently for a year from Shell.
Your car does not REQUIRE premium, but using premium will not result in a noticeable reduction in fuel mileage. Besides, you said it was getting better mileage a year ago, and you were using Premium then, right?

If they got much better mileage than you, there are only a few things that can happen. Have you moved to a location where you are doing far more city driving than before? Are you driving with the vehicle in the wrong gear, as in paddle shifing incorrectly? Has anyone else in the family started driving the car who did not drive it before? Are you certain you, or someone else, is not lead-footing the car?

Either one of the answers to the above questions is "no", or you are not telling us everything.

A car in excellent mechanical condition does not have a sudden decrease in fuel mileage without an external issue...fact!

 

Your description certainly does seems to point to driving style. Hmmm, what else can we come up with...

Are you using the car computer to come up with the mpg or are you actually calculating the mpg by recording the number of gallons purchased and number of miles driven? Car computers are incrediably inacurate with their mpg calculations... but I would expect them to be somewhat consistant.

Have you gotten new tires lately? Do you need new tires?

Were your brakes recently serviced?

Both of these should have also affected the mpg the service technician was getting... if you are confident in their honesty.

If your driving habits haven't changed has where you travel changed?

How many people drive the car?

Did the teenager next door just buy his first car but doesn't have enough money to pay for fuel?

Have you angered your spouce lately to the point she feels a need to mess with you?

 

My MPG drops 10% whenever Mrs. MellonC drives. She will not let go of the accelerator pedal from a downhill road even if there is a stop sign choosing only to stop with about 100 ft left. To her, and to a lot of people, there is no "coast" space between gas and brake pedal. It's either one of the other.........

 

I had a friend in college that had absolutely no pedal control. When he reached 56mph he took his foot off the pedal. When he then slowed to 54mph he put his foot back on the pedal... I could not ride with him. Every time I tried my neck would hurt for a week! No, his car did not have cruise control.

 

I guess you check tire pressure
is city traffic worst over the past year

I would take a long drive on a flat hiway , put on cruise a 60 mph and see what you get

 

I second this suggestion. I think doing this each direction for 1mile and averaging them would give you information about any possible drag on the car (like a stuck parking brake)

 

- Fuel injectors?
- PCV valve?
- Spark plugs and wires?

 

Well, if they returned car with 351 miles and you get less than 300 - it's YOUR driving style and drive conditions. Also, they could have really pumped as much gas as possible into tank to accomplish this but then, again, such mpg improvement should have shown itself on mpg gauge.
Hence, if you have same vehicle and one driver accomplishes MUCH better mpg under all other variables identical - it's driver. I routinely improve my wife's RX mpg simply because I have hypermiler habits from my hybrids. She's stop and go person, and stop part of it is not always at the white line.

 

honesty.. i get about 400-450km/ 250-270 miles per tank on my rx350 since new.. trip computer says about 15-16mpg on regular gas...i do about 80%city 20% highway..and that pretty light foot driving..these cars are not very fuel efficient...i do get like 26-28 mpg on the highway as advertised.. but if your in city mostly.. expect like 15 mpg..have you changed your dirving routine?