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36 votes
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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 ...
Steve Matthews's user avatar
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 ...
sweber's user avatar
  • 7,057
27 votes
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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 ...
anonymous2's user avatar
  • 5,235
24 votes
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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 ...
Zaid's user avatar
  • 39.2k
21 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 ...
GdD's user avatar
  • 17k
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 ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
20 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 ...
MadMarky's user avatar
  • 1,350
18 votes
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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 ...
JPhi1618's user avatar
  • 13.2k
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 ...
user's user avatar
  • 462
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 ...
Spehro Pefhany's user avatar
12 votes
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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 ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
12 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. ...
Solar Mike's user avatar
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11 votes
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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 ...
rpmerf's user avatar
  • 8,403
10 votes
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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.
Solar Mike's user avatar
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9 votes
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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, ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
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 ...
Gargravarr's user avatar
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 ...
andrewb's user avatar
  • 1,046
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 ...
cdunn's user avatar
  • 9,296
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 ...
rpmerf's user avatar
  • 8,403
9 votes
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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 ...
Ben's user avatar
  • 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 ...
Nick C's user avatar
  • 28.8k
9 votes
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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 ...
tlhIngan's user avatar
  • 12.2k
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 ...
Paul Ellis's user avatar
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 ...
cdunn's user avatar
  • 9,296
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 ...
Hobbes's user avatar
  • 4,412
8 votes
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Why does the engine have lesser pulling strength when the fuel in the tank is lesser?

It sounds like you have a motorcycle with a carburetor with gravity fed fuel line. (i.e. Without a fuel pump of any sort). In those conditions I can see that there is a higher fuel pressure at the ...
zipzit's user avatar
  • 6,559
8 votes
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Would not allowing my vehicle to downshift uphill be fuel efficient?

The power output of an engine is determined by how fast it can capture the energy released from fuel. There is an optimal range for that fuel-to-torque conversion, before and after which efficiency ...
ChangeMachine's user avatar
7 votes

For how long should I idle at a stop?

wear is increased at engine start When you have no oil pressure and you start the car, that is when the most wear occurs on your bearings. Crank bearings in most cars are not roller bearings anymore....
DucatiKiller's user avatar
  • 32.9k
7 votes

For how long should I idle at a stop?

fuel injected vehicles don't require a crazy amount of fuel to get started, in terms of fuel economy alone anything over 30 seconds should be safe (although we are talking about levels of fuel only ...
brettmichaelgreen's user avatar
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 ...
Dmitry Grigoryev's user avatar

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