37
votes
Accepted
Do cars consume less fuel when in Neutral?
If the car is equipped with a modern fuel injection system, it will likely use less if left in gear and allowed to run against the transmission with no throttle as modern fuel injection systems can ...
- 23.5k
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
...
- 7,047
27
votes
Accepted
Does flooring the throttle while traveling at lower speeds increase fuel consumption?
Bear with me, I'm going to clear up a myth, then answer your question. You will see that they are related.
Higher throttle doesn't mean higher RPM. Higher throttle just means more fuel entering the ...
- 5,245
25
votes
Accepted
How do the latest automatic transmissions match the efficiencies of manual gearboxes?
Traditionally...
The major drawbacks of automatic transmissions were:
parasitic losses in the torque converter, something which manual transmissions don't have.
fewer gears, so a given engine was ...
- 39.1k
22
votes
What is most fuel efficient at 130km/h?
It depends on several factors:
The car's aerodynamics
The AC compressor load
Temperature differential between the desired temp and the outside temperature
The SAE did an experiment, the full results ...
- 16.2k
21
votes
How do the latest automatic transmissions match the efficiencies of manual gearboxes?
A lot of new automatic transmissions (e.g. Volkswagen DSG) arent actually auto transmissions, at least not in the traditional sense. They have a normal computer-controlled dry clutch (well two ...
- 1,350
20
votes
Will higher octane fuel improve towing power?
That is a great question. I believe the true answer here is "it depends".
Like so many other things you can do with your vehicle, if your vehicle cannot use the higher octane fuel, it won't benefit ...
- 153k
18
votes
Accepted
Can a car AC unit be run on just the car battery?
I can't give you numbers or calculations without some work, but I can tell you than energy is never free. Cars have an A/C compressor that is mechanically driven by the engine because this is the ...
- 13.3k
14
votes
Does flooring the throttle while traveling at lower speeds increase fuel consumption?
My Volvo V70 (model year 2006) has the digital dashboard fuel consumption meter. I also have a nice, fairly long uphill climb on my way to work, so I've had opportunities to try various methods. This ...
- 452
13
votes
Can a car AC unit be run on just the car battery?
Well, Teslas (and presumably other all-electric cars) have A/C so it's not impossible, but A/C takes a fair amount of power.
On the other hand, Teslas store a lot of energy. The A/C is something ...
- 565
13
votes
What is most fuel efficient at 130km/h?
Keeping a constant speed using cruise control with windows shut and ac on because once the cabin is down to temperature it requires little to keep it there and the ac will modulate its power needs.
...
- 34.6k
12
votes
Accepted
Does leaving the choke closed increase fuel consumption
It absolutely does use more fuel. What the choke does is creates a restriction in the carburetor, which in turn creates a higher vacuum so the engine will draw more fuel when it is cold. This is ...
- 153k
11
votes
Accepted
Fuel consumption at same speed of different engine
A couple of things to contemplate:
You need a certain amount of power at the wheels to maintain a certain speed.
This assertion is (correctly) made in the question.
At 100 km/h, a typical sedan ...
- 39.1k
11
votes
Accepted
40MPG at 100MPH?
One of the reasons is loads of extra weight added by safety features and options. 8 airbags, 12 speaker stereo, 14 way adjustable seats, tons of insulation all around, power windows, power locks, 18 ...
- 8,443
10
votes
Accepted
Is manual start/stop good on older cars?
I work for a fleet delivery service. Due to safety regulations all vehicles must be shut off at every delivery point. This equals up to 150 stops a day. The starter motors fail with regularity. In ...
- 19.9k
10
votes
Accepted
What makes two-stroke engines less fuel-efficient than four-strokes?
Just so we're on the same page as to how two strokes work, here's a pic. I had to look it up because I had the wrong picture in my head.
In looking at how the cycle actually works, the power stroke ...
- 9,326
10
votes
Accepted
Driving down hill in gear without throttle
As you say you change gear from 3rd to 4th, this means you have changed the gear ratio between the engine and the wheels causing a different engine rpm.
- 34.6k
9
votes
Do cars consume less fuel when in Neutral?
If you're looking at just the fuel consumption whilst going downhill, then yes, as Steve Matthews said you'll use less fuel if you're in gear and foot off the throttle - likely no fuel at all.
But ...
- 1,046
9
votes
Do cars consume less fuel when in Neutral?
As Steve Matthews noted, modern cars will not use fuel while coasting downhill in gear. This is called Deceleration Fuel Cut-Off and uses various sensors to determine the engine load (i.e. the car is ...
- 630
9
votes
Accepted
How can vehicles run on E?
The gas gauge is just an indicator and each vehicle is going to be different. I know the older Datsun Z cars had two gas gauges, one was the main one which showed the volume of gas down to 1/4 tank, ...
- 153k
9
votes
Can a car AC unit be run on just the car battery?
The short answer to your question is no. As @JPhi1618 noted, the compressor is mechanically driven. Without the compressor you don't have any cooling. The AC runs by changing the state and pressure of ...
- 9,326
9
votes
Would not allowing my vehicle to downshift uphill be fuel efficient?
The primary reason to down shift is more power.
The 2 things effecting your gas mileage here are throttle position and RPM. As long as you can stay in 8th at less than half throttle, I would stay ...
- 8,443
9
votes
Accepted
How does cylinder deactivation work?
The link @cory posted is the description from the service manual. Just a repaste and I'll add some images and additional information.
Cylinder deactivation is accomplished by not allowing the ...
- 10.7k
9
votes
Best way to repair a rotten fuel line?
To be honest, if part of the fuel line is rotten, I'd be tempted to replace the whole line - chances are the rest isn't far behind...
Modern rubber hoses should last a decent amount of time, they're ...
- 28.7k
9
votes
Accepted
Does thick snow considerably reduce fuel economy?
Driving through snow of any thickness is increasing the rolling resistance of the vehicle, meaning you will need to use more engine power just to maintain your speed.
Since there's no such thing as a ...
- 12.2k
8
votes
Why vehicles use fuel and how can fuel economy be improved?
Vehicles use fuel because the energy in the fuel goes to these uses:
Air resistance. Because vehicles aren't moving in a vacuum, the air has a resistance force and because force times distance is ...
- 14.5k
8
votes
Accepted
Cheap vs Expensive Fuels
Gasoline is made in large batches. Each batch has a number of attributes that should be met; Octane, specific chemistry, volatility, contaminates, ethanol content, and others. The output is dependent ...
- 11.6k
8
votes
What makes two-stroke engines less fuel-efficient than four-strokes?
The efficiency of any internal combustion engine is directly related to its Carnot efficiency, where efficiency equals the inlet air temperature minus the exhaust temperature divided by the inlet ...
- 81
8
votes
Accepted
Does starting and stopping the engine lots over a short period of time in a non start-stop car damage anything?
Something to keep in mind is that the time an engine takes a great deal of its wear is cold starts. The oil isn't up to temperature yet, so parts are not separated as they should be and you get more ...
- 9,326
8
votes
Can a car AC unit be run on just the car battery?
Yes, this is possible. Several companies (VAG, BMW) have switched to AC units that are driven by electric motors. For BMW, this is part of their Efficient Dynamics strategy, where they'll switch the ...
- 4,422
Only top scored, non community-wiki answers of a minimum length are eligible