patricksr5

patricksr5

I guess I should of searched the Forum first...my bad. This seems like a well known issue. I do not remember a similar issue with my 2008 GS.

Sundaym3ch

I have 2018 RX 350L just purchased used. I drove until the 'low fuel' indicator light turned on.
My assumption is, the 'low fuel' light turns on when the fuel is below 1/8 as the fuel meter needle went below 1/8 mark.
Online manual says the fuel capacity of RX 350 is 19.2 gallons; I thought 350L was the same, if not more since it's 'little' bigger car.
But when I filled it up from 'BELOW' 1/8 mark, ~10 miles more driven after 'low fuel' indicator light came on, it capped at 16 gallons.

I thought there was a mistake so I tried to pump in some more, but it kept stopping, confirming that the tank was full. The fuel meter does show full tank.

...so I had ~3 gallon in my tank? That's when the 'low fuel' indicator light comes on? If i really did have 3 gallons, the meter should have been above 1/8 mark, as 1/8 of 19.2 gallon is ~2.4 gallons.

If my math is correct, supposed little over 7/8 of tank is 16 gallons, my 350L fuel capacity is 18 gallons. More like 17.8 gallon-ish?
Can someone confirm/enlighten me about this?

thank you

Cocal

You will notice that the 1st half of the tank goes down much more slowly than the 2nd half as in my 2017. The needle is only and indicator, I should also tell you that it is not good for the fuel pump to let go below the 1/2 mark as it likes cool fuel to keep it healthy and since there is a return of unused fuel from the line, this fuel is warm and on 1/2 a tank its effect is minimal, but and tanks almost empty it has a considerable effect on fuel pump longevity.

DocRock

Based on my experience with my 450h, I believe the onboard computer "reserves" 2 gallons of fuel when "Miles to Empty" is 0 (zero). Every time I fill up and calculate my MPG, the new "Miles to Empty" value is approximately 15.2x my calculated MPG. Given the car has a stated fuel capacity of 17.2 gallons, that translates to a reserve of 2 gallons. Lexus doesn't want you to run out of fuel, so the computer intentionally gives you a buffer so that doesn't happen. Running the tank dry can create all sorts of issues beyond the inconvenience of getting stuck somewhere with an empty tank.

dibl

I discovered this situation way back shortly after I bought my RX. On mine, the low fuel light comes on when there are over 4 gal. left in the tank -- i.e. 80+ miles of range. I asked the technology specialist at my dealer about it. He said "Lexus REALLY, REALLY, REALLY does not want you to run out of gas."

The fuel pump is cooled by the gasoline in the tank. Considering how the fuel will slosh to one side of the tank when cornering, the pump could be exposed to brief periods of running dry even when there are one or two gallons of fuel left in the tank. So the consequences of losing a fuel pump is what drove them to set the low fuel warning at such an extremely conservative point.

redhot47fl

This is interesting - and somewhat frightening - information insofar as when we picked up our new 2021 RX350 two weeks ago, the dealer's make-ready department had failed to make it ready. They almost sent us on our way with virtually no fuel in the tank - and with the tires preposterously overinflated to 55 psi. Luckily, we caught both failures before we took to the road for a three-hour trip home.

dibl

That's the type of dealer incompetence that really needs to be reported to the US corporate office, IMO.

Mmuscat80

I purchased a 2020 CPO RX a few weeks ago with 28k miles on it. I'm noticing that the fuel sensor is incorrect. I'm getting about 21 mpg, however, my range on the car's computer is only showing about 330 miles when full. Today I filled up, the car read empty, gas light on and range said I only 1 mile left, however, it only took 16 gallons. This is really frustrating to me, as I drive a ton for work (put 1300 miles on in the 2 weeks I've owned it), and I hate having to stop for gas. I've got an appointment at the dealer to have this looked at, but is this a common problem?

dibl

YES, however Lexus does not consider it a problem. The sensor is designed to scare you in to the gas station when there are still 2 or 3 gallons left in the tank. The reason is that there is a fuel pump inside the gas tank, which depends upon the gasoline for a coolant. If you actually run very low on fuel, that fuel pump can burn out, resulting in (a) a dangerous breakdown on the road, and (b) a rather expensive repair job.

So the reality is, you don't have a range of (19.2 gal. x your mileage). It is more like (16 gal. x your mileage). Thus your sensor design.

Bear in mind that when the fuel is running low, merely driving around corners can slosh the remaining fuel away from the fuel pump. So this is not a scenario that you want to push to the limit.

There is a "sticky" mileage thread on this general topic, in the top section of this forum.

jrobe

If this is the only problem I ever have with my Lexus, I will be very happy.

I can go about 350 miles between fill ups. The last thing I want to do is run out of gas on the side of a busy freeway with endless semi-trucks and speeders flying past me 3 feet away. I won't even let my car get to the point where that warning light comes on. These must be good cars if this is a "problem."

stlgrym3

iTrader: (4)

mine only shows 310 miles on a full tank of gas, it was around 330-350 miles before. fueleconomy.gov shows 422 mile range for the exact model. why such discrepancies? what is your range on a full tank of gas? is that number calculated from the previous tank's mpg figure? i know last couple tanks of gas the mpg numbers were pretty bad, but that's for another discussion.

ravenuer

I'm not sure but I do think it's calculated from the previous tank. Otherwise, what would it have to go by?

bamalam

Government fails once again. The brainiacs /s at fueleconomy.gov just took their 22mpg "combined" mileage and multiplied it by the RX's 19.2 gal fuel tank capacity. 22 x 19.2 = 422.4. That number assumes you run the tank bone dry. Given that the tank includes a low pressure fuel pump that depends on fuel for lubrication, it also means you'll be replacing that pump very often if you try to duplicate the government's numbers.

My practical reality is that I get 280-330 miles on a tank. I do a little better occasionally with lots of highway miles on flat terrain. (My RX is not an F Sport, but the F Sport package does not materially affect mileage or range.) It does appear that the Range figure after a fill-up is based on the mileage from the last tank. At least that's my anecdotal experience. BTW, I've run my RX down to zero miles remaining on the Range display, and never put more than ~16 gallons in the tank. Lexus tries to protect drivers from themselves, at least with respect to low fuel problems.

FastFord

Mine is all over the map. If I go on a road trip, after about 50-100 miles it doesn't move, sits at range 260 for 20-30 minutes. City driving it goes down too fast lol

I usually just go by what the gauge looks like, and rarely let it get low anyway. Hey 60 MPH with a good tail wind you might get 30+ MPG