Just had my first fillup since getting the car. I pulled into the gas station with the fuel light on and the trip computer telling me that I have 17 miles left of gas, with a tank average of 21.8 MPG...

My highly advanced math skills tell me that the 'puter thinks there's less than a gallon of gas left.

To my surprise, at the gas station, I only filled 14.5 gallons, which, using the same advanced math, means there's potentially 2.7 gallons of gas left in the tank. I'm pretty sure the dealer filled it up initially, as I went with him on the gas run.

I'll test this again the next time I get gas, but given the rate I get to drive the car (400 miles since 12/23), it'll be a while. What are your observations regarding the trip computer and the "real" amount of gas we have in the car at each fillup? Thanks.

-KC

 

I think you are close. I noticed the gas light seems to come on pretty early.

 

okay. the light on all lexus cars come on around 2-3 gallons left. However, the trip computer is the one that is not correct. It will never be exact. What is says is not how many miles you can actually drive. It is based on previous driving mpg averages. the car cant actually "weigh" how much gas is left. all these numbers are estimates.

now my second point is that you should never wait till you see the light to fill up. In fact, a lot of people dont let it drop below the last tick mark if possible because of all the "stuff" that floats in the gas.

 

Right, I understand that the computer isn't meant to be precise, but assuming it takes the data from your most recent usage, i.e. the MPG for this most recent fillup, which for me was 21.5+... It still was way too conservative by 2 gallons. Now that I know, I can plan accordingly...

Is there a definitive answer on this? I hear both sides. Don't let it get past 3/4 empty, it's fine to drive until the last liters, don't mix gas brands if you can avoid it, etc... Just for my own convenience, I'd rather maximize my range per fillup, but I'll change my habit if there's strong opinions/evidence that this is bad for the car... Thanks for your advice guys.

-KC

 

ok, from my experience with all the cars i've driven, the light would come on with 2-3 gallons left depending on manufactures, which is very typical. As for the computer, i have driven the car for another gallon or so AFTER it hits 0 miles left, but it is not recommended to do because you are really pushing it once you hit 0 miles, i doubt there's anymore than 1 gallon left so you should really find a gas station when it hits 0, that's kinda like your last warning..

 

With almost 7k miles on my IS, I can confirm that when the low fuel light turns on, you have apprx 3 gallons of gas left. My experience also shows that when the trip computer hits 0, you usually have at least 25 miles to go before being truly empty, but I don't recommend that you test this too often. Also, it's an urban myth about the debris in your tank, since all modern gas stations have advanced filtration for the gas you pump. I usually drive until the low fuel light comes on and then fill up, never been stranded by the side of the road yet . . .

 

Sheeeeeet..i tested that theory..and got burnt!!! ..sure the gas LIGHT came on way before but when range says 0. i was out of gas in like a mile....first time i had to use roadside assistance

 

The fuel system may be able to hold 17 gallons, but that doesn't necessarily mean that it can actually use the whole 17 gallons. I've coasted into stations before with other cars, and have NEVER been able to put the rated volume of gas back in.

Regarding when to fill back up, I always wait until it's as close to empty as it can be while still being practical. I would rather enjoy better performance and fuel economy (less weight), and spend less of my life at the gas station.

 

The most Gas I have ever put back into my car was 16.1 gallons. The car said I still had 30 miles left. That was the scariest trip to the gas station ever. I never got so antsy on the interstate before!

 

Methinks you have an extra heavy right foot . . .

 

I'm glad you said that. I didn't want to admit that I was influenced by years of watching Formula 1 racing (pre-refueling) where the cars performed signifcantly better on the empty tank...

yes yes, I know that 2 extra gallons of gas won't make that much of a difference, but I still get the irrational good feeling that driving at the end of the tank, you are at your most fuel efficient (or peak performance)...

I guess I should just lose 15 pounds myself...

 

I think the gas pump must have been miscalibrated. Either that, our your fuel guage sensor is hosed up. As many have said, it shouldn't take much more than 14 gallons to fill up the tank even when the guage and "miles remaining" gets to and indicated 0.

 

or that the poster is the only one with an accurate gauge, since 30 miles with 1.1 gallons left on an interstate trip is pretty close...

Either way, bottom line for me is to play it safe and either 1) not let the computer miles left hit 0 or 2) at most stretch 30 miles after the light first comes on.

 

As I learned from that trip there are varying degrees of how bright the gas light LED gets. Call me crazy but it went from a soft orange to a blazing bright one.

My gas pointer was below E.

Dumb me I have a 90 mile round trip and neglected to fill up once I got under a quarter tank. In my estimation each quarter of gas is roughly 100 miles. At half tank I'm at about 220.

And I don't think my pump is wrong. My milage meter is usually off on the low side by .3 or on the high side by a mile. I usually just take how much gas I put in the car divided by the mileage I used. = / It has yet to fail me or be off more than a mile. Or is my calculation incorrect? I reset my everything everytime I fill up. = /

 

IMO, the trip computer will be more consistent than the pumps at the gas station. Unless you pump your gas at the same exact pump every time with the car sitting in the same direction on the same patch of concrete and top it off at the exact same level ... your method of calculating will be less consistent.