# Tag Info

31

According to wikpedia, the volumetric constant of thermal expansion for gasoline is av=950*10^-6/K For example, if the temperature changes by 20K (20°C; 36°F), the volume changes by a factor of 950*10^-6/K * 20K = 0.0192 The warmer fuel has a volume increased by about 2%, and since energy content depends on the mass, the energy per volume decreases by ...

27

Your fuel economy change is caused by the fact you're not using the same fuel. Fuel changes twice per year from summer blend to winter blend and back again causing a change in the Reid Vapor Pressure (RVP). In summer, the hotter temperature evaporates liquids easier causing more pollution, so it is blended to lower the RVP. This blend is more costly to ...

11

Generally, these systems don't activate until the engine is warm, so you probably won't see it for the first 5-10 minutes of your journey - of course it largely depends on the nature of your journey as to whether that's useful or not, plus, as Solar Mike says, what you consider useful. For example, if your half-hour journey is 20 minutes pottering through ...

7

Many countries (but notably not US) actually have regulations regarding temperature compensation of fuel volume. For example, UK has Standard temperature accounting for fuel dispensers, which allows the volumetric measurements to be corrected for the standard temperature of 15°C. Needless to say, it makes no difference when to tank in this case, as you ...

7

The simple fact is, it's all just mathematics. For instance: (Note: I'm just throwing numbers out here, it's the mathematics which are important.) Given: 20 gallon fuel tank If you are using 93 octane fuel, get 20mpg, and it costs \$2.40/gallon At 20 gal and 20mpg, that's a total of 400 miles travel distance. 20 gals of fuel at \$2.40/gal, would equate to \$...

5

Setting all other variables aside for a moment, "racing around" is something ill-defined and quite subjective, but it is entirely plausible that something like hard acceleration, while not in the short term, can get you better mileage in the long run. To understand why this might be the case, you need to understand the power band. An engine's performance ...

5

There is Brake-Specific Fuel Consumption Which is a measure of how much fuel is consumed per unit energy. Another way to look at it is the rate of fuel flow needed per unit power developed by the engine. This information is not something accessible through OBD-II. But it's not very useful in this case Note that MPG remains relevant because it is a ...

5

Looking at the market, VW has built the VW XL1 (EN, DE), a hybrid car with up to 260mpg. The german site says there was a test drive on the street where the car indeed consumed 0.89l diesel /100km, which equals 240mpg. But there are also many other confusing numbers, giving up to twice the consumption. I also find 1.82 l/100km with full and 1.94l/100km with ...

5

Several things come to mind (though I'm sure there's a lot more): O2 Sensor: As the front O2 (or lambda) sensor gets older, it gets lazy (doesn't react as quickly). Due to this, as they approach end of life, you'll start seeing declining gas mileage numbers. MAF Sensor: Your Mass Air Flow (MAF) sensor detects the amount of air being taken into your engine. ...

5

This depends on driving conditions, mainly speed and temperature. AC fuel consumption increases with temperature fuel consumption due to open windows increases with speed The SAE found that AC is more efficient at highway speeds. Modern cars incorporate tricks to reduce AC fuel consumption: the AC compressor is preferentially engaged when you're slowing ...

4

60 MPH assuming you are in the same gear at both speeds. At a constant gear, your engine turns at a fixed ratio to the distance you travel. So if you travel from A to B your engine will always turn X revolutions, regardless of speed. In other words, the piston experiences the exact same number of cycles regardless of 60 or 70 mph Air friction increases ...

4

There are two schools of though on this subject, at least in the UK. For the sake of fuel efficiency you should drive in the highest gear that your engine sounds happy with. At 30MPH in a 5 or 6 speed manual car that will probably be 4th. The other school of thought (for the sake of road safety) is that if you stay in 3rd gear you are more likely to notice ...

4

As @sweber said, the tanks are usually underground, which keeps their temperature constant. However, if you are filling a smaller bottle with gasoline (ex: for a small engine), the first few gallons (litres) that come out of the nozzle will be a slightly different temperature. This is because the pumps are above ground, and if they are sitting in the sun, ...

4

Another reason: Winter tires. Choose between hard tires (good fuel economy, REALLY bad on snow) or soft tires (worse fuel economy, good on snow).

4

Your vehicle does not operate at maximum efficiency until the engine has reached its normal operating temperature. This is generally when the coolant temperature reaches about 200 degrees Fahrenheit. In the winter it takes the engine longer to reach that temperature simply due to the colder ambient temperature.

4

tl;dr: Your indicated estimate of range to empty will always lag the actual fuel burn rate since the system collects data over time to estimate future performance. I think you've found a situation where the running estimate of the range to empty given your remaining fuel is lagging a bit behind the actual data. Let's do the math. Your Altima has an 18 ...

4

When I had about 60 000 km on my 2011 Toyota Yaris with start/stop, the start/stop meter showed the engine had been stopped for 14 hours. So, 300 000 km, a useful lifetime of a car, means the engine will be off for 70 hours. At 0.7 l / hour, this is 49 liters of saved fuel. Depending on the fuel costs, the expense may vary, but it'll probably be below 100 ...

4

The commands to read out Speed, RPM and some other sensor data was well as fault codes are standardized for all cars and commonly known. That is, one can "easily" develop some software to read out these, and even to reset fault codes. But all other functionality like reprogramming/tweaking the ECU are implemented by the manufacturer, and each manufacturer ...

4

It's true that heated O2 sensors shorten the time the engine is in open loop. So the whole "wasting gas thing" while you wait for the engine to warm up isn't as big an issue. But there are many other reasons to not sit and warm up your engine. The most important one is that warming your engine will warm the coolant, but it doesn't warm the oil as quickly as ...

4

Combustion engines have greatly varying degrees of efficiency, depending on the load and rpm. This is usually shown in a specific fuel consumption diagram like this: Generally, lower speed and higher load results in less fuel required for the same amount of power. This applies to electric motors too, but is far less pronounced there - to the point where it ...

3

My answer is - yes, gas engines are affected in the same ways by hills and wind... but that doesn't mean surface streets are the better option. When you look at the question as a raw physics question you find the answer that all resistive forces do not discriminate between drive type. Doesn't matter if you all electric, hybrid, gasoline, diesel, car, truck ,...

3

In the winter the ambient air is much colder, making the air more dense. Denser air will contain more oxygen and so the car will inject more fuel in order to maintain the correct ratios. This effect could be exaggerated by the fact your car is turbocharged and that the inter-cooler will be working much more efficiently in the winter, further reducing ...

3

If "racing around" means generally higher speeds, then you could get better economy because you happen to be in a higher gear. The best economy comes about at low rpm but in a high gear. If you drive a manual, shift up soon without lugging the engine, get to top gear and stay at low revs there for the best mileage figures.

3

While @Robert-Ryan is technically correct, I'd be surprised if there was a measurable difference in engine lifetime. Engine wear is dominated by cold starts. Once the engine is thoroughly warm, engine wear is minimal. If you want to maximize engine life, minimize the number of short trips where the engine doesn't get warm, or invest in an engine block heater....

3

Some obvious factors that haven't been mentioned. Weight - if you carry a full load of passengers (or other heavy stuff), mileage will drop. Aerodynamics - open windows, add-ons like badly-adjusted spoilers, and dented or missing parts of the body will drag you down, especially when driving fast. AC - adds directly to fuel usage the more often and intensely ...

3

Well, I find my car will run much smoother after giving it a 750km run at 130km/h only stopping once for fuel... Really does get it properly warm and cleans all its pipes. Took an old RV / motorhome on a long run (2 week holiday) with constant speed running - that also made a difference : before all it had done was small local running around and was ...

2

There is no way (to my knowledge) to affect the displacement of an engine while it's running (dynamically). You can, however, change the two working parameters of an engine dynamically, those being the volumetric efficiency and compression ratio. Volumetric efficiency (VE) is explained as how well do the cylinders fill with air/fuel mixture during the ...

2

Using the heater has no effect on fuel consumption. Using the heater won't lower the engine temperature because the thermostat will keep the engine temperature constant. It may actually use a tiny bit more gas from the electrical draw because of the blower motor.

2

Do not forget how long has elapsed since the last vehicle service. This is important because components like spark plugs require regular replacement to keep your engine efficient. Also, things like the condition of the brakes can have a massive effect on gas mileage. For example, a brake that isn't releasing cleanly and hangs on slightly is akin to ...

2

It's obviously not like: 10% lower octane is 10% less timing advance, 10% less power, and 10% more fuel consumption. I don't think it's even possible to calculate beforehand how much you will benefit or not from lower or higher octane fuel, even if you precisely know how the ECU will react. And that's the thing: It heavily depends on how the ECU deals with ...

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