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
...
- 7,057
27
votes
Accepted
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 (...
- 1,533
11
votes
Accepted
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 ...
- 28.9k
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 ...
- 2,652
7
votes
Are fuel efficiency charts available for mainstream engines?
Is there a way to find such a chart for the engines in real world popular cars?
Not unless the engine manufacturer had seen a reason to publish the chart. In most cases, they probably have no ...
- 15.3k
5
votes
Accepted
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 ...
- 4,412
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, ...
- 7,057
5
votes
Accepted
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 ...
- 219
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 (...
- 5,245
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).
- 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. ...
4
votes
Accepted
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 ...
- 24.5k
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 ...
- 15.3k
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 ...
- 7,057
4
votes
Accepted
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 ...
- 1,392
3
votes
Accepted
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 ...
- 34.7k
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 ...
- 4,412
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 ...
- 3,264
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 ...
- 159
2
votes
What causes a 20% difference in fuel economy between winter and summer?
Presumably in winter you'll have lots of additional systems switched on such as the heating, demisters, headlights, etc...
All of these things sap your fuel consumption.
- 23.4k
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 ...
- 2,954
2
votes
How much can sub-optimal octane affect efficiency or power?
I can't tell about precise numbers, but have some experience with my cars and multiple gas types usage: if a lower octane is used in an engine tuned for higher octanes, the engine looses power a lot. ...
- 3,356
2
votes
Is it more efficient to drive with the windows down or the AC on?
TL DR: Windows down w/o AC nets better fuel mileage.
There was an episode of Mythbusters which covered this subject. They found windows down without A/C will run significantly further than will a ...
- 162k
2
votes
Ethanol or non-Ethanol?
small engines don't need the extra octane and the extra octane won't produce any higher efficiency. However, non-ethanol gas doesn't attract water link ethanol gas, so it doesn't corrode the inside of ...
- 1,392
2
votes
Accepted
Compression ignition in petrol engines
Don't understand the down votes. Mazda has been doing considerable research into this and is releasing a new line of engines soon called Skyactiv-X to be rolled out in consumer models. It is 20-30% ...
- 175
2
votes
Why do Electric Vehicles have higher fuel efficiency at sub-highway speeds?
It is unclear to me what you are comparing with what
electric vehicles in the city vs on the highway
city usage of combustion vs electric.
For both types, the most efficient energy use will be at a ...
- 2,473
2
votes
Accepted
What is the logic behind retractable spoilers?
In a way you have answered your own question.
The DRS wing is there to keep there vehicle planted on the road to allow the vehicle to maneuver bends at high speed. At certain straight 'safe' ...
- 25.5k
1
vote
Accepted
Where and how is engine torque measured when producing an engine map?
The manufacturer's put their engines on dynamometers during the design and build phases.
In fact, there are test engines designed to be varied in many ways to test different parameters, one ...
- 34.7k
1
vote
Ethanol or non-Ethanol?
Consider this:
What costs $2.50 per gallon of E10 costs $2.50 / 0.9 = $2.7778 per gallon of actual gasoline in it.
So, if you're wondering if the smaller energy content of ethanol is an issue, don't!...
- 15.3k
1
vote
Why don't automatic transmissions include Neutral in their range?
Let's for simplicity assume going to neutral does save the same amount of fuel as operating the engine in overrun.
Then it'd still be the wisest to choose to overrun the engine rather then selecting ...
- 2,954
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