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I have a Toyota C-HR Hybride Edition 1.8L 2020. I see in the specification that the fuel tank is 43L.

With every trip, when I turn off the car, I get fuel consumption statistics for the current trip. always between 3.7 and 4.1 L/100KM

I refuel only when the fuel warning is ON. so let's assume that I consumed over 40L.

With this assumption, if on average I consume 4L/100Km (most of the time less), I'm able to make 40*4 = 1600km !!!!!. but I'm only able to make less than 700km.it's less than half.

So in summary I consume 8L/100KM on average. How it's legal that the manufacturer's specification is so misleading!!

Anything I missed

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    You can't assume how much fuel will go in the tank, and the inline meters are not very accurate. The way to get the fuel consumption is to fill the tank and record the odometer reading. The consumption is the fuel used to refill, the distance is the difference from the odo reading at the previous full tank refill. Jul 19, 2022 at 17:42
  • when you stop the car, you get fuel consumption statistics for the current trip. always between 3.7 and 4.1 L/100KM Jul 19, 2022 at 17:44
  • @WeatherVane yes, so with those calculations, the car consumes 8L/100km. double than the claimed one Jul 19, 2022 at 17:48
  • There are often different settings for the fuel consumption available (like since refuel, short term, long term), and it's going to depend if you've been doing a lot of town driving, with regen electricity. Out of town, a hybrid won't get any better consumption than conventional, and 8L/100Km isn't very bad. Jul 19, 2022 at 17:51
  • @makouda - What Weather Vane is saying, take ANY guess work out of the equation. If you have both the exact amount of fuel used and the exact amount of distance traveled, you'll have your answer and it will be exact. What is on the dash is an "indicator" and nothing more. You cannot trust it to give you an accurate read of what is going on. It's just there to give you an idea. Jul 19, 2022 at 17:53

2 Answers 2

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When looking at fuel consumption, there is always a lot of "fudge" factor involved which makes getting accurate results difficult. As the saying goes: "your mileage may vary"

Following are just some of the fudge factors that will lead to inaccurate fuel economy measurements and differences between actual and advertised economy. These are all very small sources of inaccuracy, but they add up.

Fuel used

There is really no good way to accurately know the actual amount of fuel used without adding calibrated metering equipment. Unless you own your own fueling station, you cannot control when the pump shuts off, what the temperature and volume of the fuel is, and even which pump you use from time to time. It is also impossible to tell how much fuel was left in the tank unless you run it completely dry (which isn't a great idea for lots of reasons :)) so you're left with a rough approximation.

The amount of fuel used is also calculated by the car, but that generally relies on a calculated value from fuel injector duty cycle and an assumed amount amount of fuel per pulse. This will be slightly off due to the type/quality of fuel, fuel pressure, cleanliness of injectors, electrical and fuel line wear, etc. So that, also, is only going to be an approximation.

Distance traveled

Here, again, we are dealing with calculated values based on assumptions. Your car calculates how far it has been based on measured revolutions of the wheels, but it uses assumed values for tire size, tire inflation, etc. so it is also a rough approximation. If you run a non-standard tire size or run your tires in a very under- or over-inflated state, the numbers will be slightly off. Once again - small variation, but adds up over time.

The above variations only address the difference between your measured fuel economy, and the car's displayed fuel economy. Below is the big wildcard, which accounts for the wide differences between your actual fuel economy and what the carmaker says the car will do.

Your driving style and location

Simple. If you drive in very hilly areas, your economy will generally be worse than if you do all your driving in flatlands. Similarly, if you stop and go a lot, your economy will be worse than if you start once and cruise for long periods. Heating/cooling load and electrical load also contribute.

If you are lucky with location and careful with driving style, you can make a Mustang get 40 MPG and by the same token, if you wish, you can make a Prius get 15. Advertised values are based on standardized test cycles that only slightly approximate the real world.

Finally, those are the only factors for cars with a single source of motive force. Yours has another - the electrical motor. The amount of drag or boost provided by the hybrid system is another factor that adds imprecision.

All that boils down to say that advertised fuel economy is really only a very rough estimate of what the car can/will do.

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You have incorrect units

Let's see what the units of 40*4 are.

40 is measured in liters. 4 is measured in liters per 100km.

So the units of 40*4 are liters squared per 100km. Besides, 40*4 is not 1600 unlike you claimed, but rather 160.

What does this 160 liters squared per 100km tell you? Nothing.

You should have calculated this:

40 liters / (0.04 liters / km) = 1000 km.

So what is happening here is that your 40 liters is probably way off. Although the tank may have 43 liters, the fuel light is probably turning on far earlier than when 40 liters is consumed. If it's turning on at 28 liters consumed (15 liters left), then you would get 700 km.

It's also possible that your refueling style doesn't allow the entire 43 liters to be used. It's possible that the gas nozzle thinks the tank is full already when you have 38 liters. If this is the case, then the fuel light would be turning on not at 15 liters left but at 10 liters left.

You could fit the full 43 liters by "trickle filling" the tank after the fuel flow has already stopped, but I don't recommend that. Fuel expands with temperature very quickly. If you put in the full 43 liters when it's cold, then on a hot sunny day the fuel may not have enough space to expand into.

According to a Google search "fuel light liters left", the first result that Google highlighted to me says there's about 10 liters left when the fuel light comes on. So that would be consistent with you filling the tank to only 38 liters -- which is good, since there's five liters of extra room for the fuel to expand on a hot day. I suspect for that tank size two liters of extra room could be enough, though, so you may be able to put just a little bit more extra gasoline in.

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