31 votes

At what time of day/temperature should I refuel my vehicle?

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 ...
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  • 6,997
27 votes
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What causes a 20% difference in fuel economy between winter and summer?

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 (...
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  • 1,518
11 votes
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Will I be better off turning the start stop function off?

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 ...
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  • 28.6k
7 votes

At what time of day/temperature should I refuel my vehicle?

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 ...
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7 votes

How can I determine if it is more cost effective to run premium fuel in my car?

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 ...
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5 votes

Fuel Consumption Paradox

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 ...
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5 votes
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Alternative fuel consumption metric to MPG to measure actual engine efficiency?

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 ...
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  • 38.9k
5 votes

Is Tom Ogle's 100+mpg engine actually feasible?

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, ...
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  • 6,997
5 votes
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What non-driver, non-terrain factors can affect vehicle miles per gallon?

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 ...
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5 votes
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Is it more efficient to drive with the windows down or the AC on?

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 ...
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  • 4,402
5 votes
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Why do Electric Vehicles have higher fuel efficiency at sub-highway speeds?

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 ...
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  • 219
4 votes
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What would be better for an engine driving at 60mph or 70mph? I wish to get the most miles out of my engine?

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 ...
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4 votes
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Is there correlation between fuel efficiency and preferred gear at certain speed?

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 ...
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  • 1,658
4 votes

At what time of day/temperature should I refuel my vehicle?

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 (...
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  • 5,216
4 votes

What causes a 20% difference in fuel economy between winter and summer?

Another reason: Winter tires. Choose between hard tires (good fuel economy, REALLY bad on snow) or soft tires (worse fuel economy, good on snow).
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  • 145
4 votes

What causes a 20% difference in fuel economy between winter and summer?

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. ...
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4 votes
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Trip computer gives inconsistent remaining mileage estimates

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 ...
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  • 24.3k
4 votes

Will I be better off turning the start stop function off?

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 ...
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  • 13.4k
4 votes

Could the OBD2 connector be used to switch gears?

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 ...
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  • 6,997
4 votes
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How are new cars (with HO2Ss) affected by cold starts?

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 ...
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  • 1,316
3 votes

Is a gas car as sensitive to terrain as an electric?

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 ...
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3 votes

What causes a 20% difference in fuel economy between winter and summer?

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 ...
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  • 159
3 votes

Fuel Consumption Paradox

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 ...
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3 votes

What would be better for an engine driving at 60mph or 70mph? I wish to get the most miles out of my engine?

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 ...
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  • 4,402
3 votes

What non-driver, non-terrain factors can affect vehicle miles per gallon?

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 ...
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3 votes
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How effective is Italian tune-up?

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 ...
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  • 34.4k
2 votes

Does the size of engine cylinder affect the efficiency?

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 ...
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2 votes

Does using heat in the car SAVE gas?

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 ...
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  • 15.9k
2 votes

What non-driver, non-terrain factors can affect vehicle miles per gallon?

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 ...
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2 votes

How much can sub-optimal octane affect efficiency or power?

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 ...
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