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Still learning about the milage thing since delivery yesterday. I drove 150 miles from dealer to home. I got around 30.9 mpg. I saw the sticker had 39 mpg and I said to myself - what did I do wrong? I tried to keep below 75 mph for the "break-in" period. Now it looks like I will probably only expect something around 31 +/- mpg, not 39, right?
As to the main topic here: I tried on my other car before and knew that the manufacturer probably worried that some people will run out of gas on the highway so they tell you 0 miles now - still secretly keep 1-2 gallons for you to find next gas station. I did a few times by only refilling the gas after the car reached miles. My wife was not happy!!
Now for the peace of mind, after the gauge is below 1/4, I will look for next gas station.
To calculate the MPG manually, one might want to use the SAME station SAME pump so that the auto stop will stop at the same level. The error of 1-2 mpg is no surprise to me. As I also know, the speed is also 1-2 mph higher than the actual speed measured by GPS???
For my other car, if I need to continue to drive after refilling the gas, I usually add more gas - just save a few miles interval before my next gas station visit. I can always add more than 1 gallon...
Originally Posted by SeismicGuy
I noticed thata "shut-off" was mentioned a couple of times in previous posts. I assume you are talking about when the pump nozzle shuts off by itself when fueling and this is one of my small peeves with this vehicle. With most vehicles I can always add a bit more after the pump auto shut-off. With the NX it seems to shut-off long before it needs to and I can always add quite a bit more fuel. Maybe has something to do with the shape of the tank or the filler tube?
For my other car, if I need to continue to drive after refilling the gas, I usually add more gas - just save a few miles interval before my next gas station visit. I can always add more than 1 gallon...
Just adding some more info into this subject of calculating gas mileage. It's really not all that black and white as you would think.
There are government regulations in Canada and USA and I'm sure elsewhere in the world too. Gasoline pumps are calibrated on a regular basis, look for a sticker applied to pump which states the last time it was calibrated and when it is due again, this is the law. Also gasoline volume pumped as stated on the gauge in Canada is calculated at 10 degrees Celsius as gas expands and contracts in volume based on its temperature, this is also done in USA using Fahrenheit. It's my understanding the change in volume is very slight, but never the less does exist. So gas volume is more dense when cold and has more volume or less dense when hot.
The shut off system used on gasoline pumps are also complex and are prone to wear over time and thus they actuate or stop the flow of fuel slightly differently from pump to pump as their state of wear are unique to each pump. This video shows how a gas pump nozzle works ( yes it will make your brain hurt and it's 14 minutes of your life you won't get back ) You will see there's lots of moving parts, o-ring seals, small air holes etc that all can contribute to exactly when the pump will shut off.
Also the reality is that gasoline in warmer weather does evaporate too, that's why cars have an evap system to catch the fumes. So gas mileage will ultimately be affected if you fill up in warm temps, don't drive enough to consume the tank while it's still all liquid and not fumes etc. The fumes that are captured are burned up when the engine is turned on next, but your mileage isn't the same using fumes instead of liquid gasoline.
I too have confirmed with my '22 NX350h that there's about 10 litres or 2.6 US Gallons left in my fuel tank when it says 0. I also noted when I first picked up my car it stated I had over 900kms (559 miles) till empty. Now with all my data, even after clearing the mileage memory, I can't get anything over 700 kms to empty.
USA EPA Testing Procedure for mileage (see link). Note that there is not much 'highway speed' in Highway and High Speed test procedures. See graphs. And rates of acceleration are quite mild. So achieving highway gas mileage ratings going 60 + mph constantly won't cut it.
I always hand calculate my mileage. My 16' RX350 calculated mileage was always +/- 0.2 MPG of what the computer said. My 22' NX350h difference is +/- 2.0 MPG! Most of the time my empty light comes on & car says I have ~17 mi to empty. When I fill up, it takes 11 gallons (3.5 to spare). One time, empty light didn't come on until 585 miles on tripmeter. I put in 14.3 gallons (running on fumes!). I don't trust the NX computer readings and reset my trip meter and fill up at 450-475 miles.
Will the hybrid car computer calculate this with the EV battery in consideration and your driving habits/history? If you always push the pedal harder to accelerate vs you have more downhill to drive thus charging the battery with more efficiency - that will make a bigger difference...
I usually fill when I'm at 1/2 tank. Even then I'm always shocked by how seldom I ever look at the fuel gauge. Average fill is monthly or a bit more. I calculate mpg every tank but it's obvious there is some elasticity in how much the fill takes. So my 'official' score is the total average MPG shown on the dash display. Currently at 44.9 (premium fuel) and that is very close to my eyeball calculation from my data set.
I lease my cars for the last 10+ years as I want new features/tech all the time. Every time I pickup my car, they always remind me not to fill it up after it stopped and did mention about damaging the "Charcoal Canisters"
I tried not to use the gas down to the warning light because of the fuel pressure sensor replacement and similar costs to replace a Charcoal Canister.
As many have stated, fill it up at 1/4 and enjoy the car as 1-2mpg delta is acceptable this day
OP here - interesting read on the thread. Just to re-iterate, I'm not concerned about how much the tank actually holds, the distance-to-empty (which is skewed to make sure you always have gas left), or even what mpg I'm getting.
I do use the same gas station every time, though not necessarily the same pump.
(and FYI I do the "update" on the trip mpg screen before I leave the station, so that every time I fill my instrument cluster is showing me the mpg on the current tank)
My only concern was that when I pull into the gas station and I've driven X miles since the last fill, and the car says I got Y mpg since the last reset, I should have to put in X/Y gallons to fill up again, but I always have to put in more (usually ~5% more) than that. You could say I'm overfilling, but unless the gas is leaking out somewhere, that would be impossible to happen every time! If I wasn't truly full when I started, then the next time I could put in more than the car burned, and I'd calculate less than the dash shows. But in that case, the prior time I would have calculated a higher mpg (like, if I drove to nearly empty, and only filled halfway up, I'd say WOW, I got 80 MPG on that tank because I drove 400 mi and only put in 5 gallons!)
Over a long period of time, it should average out and I'd be fine with it reading high one time and low another because of the difference in the pump shut-off or how much I squeeze in. But the car always claims I got 1-2 mpg more than reality, except for once which is not enough to make up for all the other times
Maybe this is evaporation? But if my car is evaporating 1/2 gal into the atmosphere every 3 weeks or so, isn't that a problem?
Maybe this is evaporation? But if my car is evaporating 1/2 gal into the atmosphere every 3 weeks or so, isn't that a problem?
You would get a check engine light if you had this level of evap occuring. Evap control systems are pressure tested by the vehicle regularly, this is similar to why you'll light up your dash lights if you forget to properly secure your gas cap. Your issue sounds like every Toyota/Lexus product I've owned in the last 20 yrs, they all tended to be slightly optimistic as well as a few other mfr cars I've had. Some are a bit more accurate than others, but I've never seen a car that consistently under rates the MPG on the calculated display, even a tiny bit. As the old saying goes "don't worry, be happy", once you know the typical error rate for your conditions and fuel usage, you just factor it in to bridge estimates to reality.
And besides that, the MPG display on the dash will always just be an estimate, even if slightly estimated high. Your car doesn't actually know how much fuel is injected with each pulse at each injector. It knows injector pulse duration, approx fuel pressure, nominal fuel rates for a stock injector, and the result of (or lack of, in the case of a misfire) combustion, but how much fuel actually makes it out of each individual injector is, well, an estimate. The difference in amount of fuel injected per pulse between your actual MPG and calc MPG is on the order of less than a microliter of fuel (an amount not even visible to the naked eye).
You would get a check engine light if you had this level of evap occuring. Evap control systems are pressure tested by the vehicle regularly, this is similar to why you'll light up your dash lights if you forget to properly secure your gas cap. Your issue sounds like every Toyota/Lexus product I've owned in the last 20 yrs, they all tended to be slightly optimistic as well as a few other mfr cars I've had. Some are a bit more accurate than others, but I've never seen a car that consistently under rates the MPG on the calculated display, even a tiny bit. As the old saying goes "don't worry, be happy", once you know the typical error rate for your conditions and fuel usage, you just factor it in to bridge estimates to reality.
And besides that, the MPG display on the dash will always just be an estimate, even if slightly estimated high. Your car doesn't actually know how much fuel is injected with each pulse at each injector. It knows injector pulse duration, approx fuel pressure, nominal fuel rates for a stock injector, and the result of (or lack of, in the case of a misfire) combustion, but how much fuel actually makes it out of each individual injector is, well, an estimate. The difference in amount of fuel injected per pulse between your actual MPG and calc MPG is on the order of less than a microliter of fuel (an amount not even visible to the naked eye).
Thanks! This is probably the best explanation I've gotten. I'll just be annoyed by it but have to set that aside!
And the real reason I was tracking this so closely, honestly, was to figure out the real distance to empty, and now I have enough data to know that when it says 0 it is at least 40 and more typically 70 miles, so I can drive another 30 if that's where the next exit is and not be in a panic.
03-30-24, 04:34 PM
Don't overfill
) You will see there's lots of moving parts, o-ring seals, small air holes etc that all can contribute to exactly when the pump will shut off.
