37

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 and do shut down the injectors completely thus use no fuel whatsoever. If the engine is at idle in neutral, the ECU will have to use a small amount of fuel to ...


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

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 combustion chamber. This will tend to accelerate your engine, but if it's under an accelerating load (increasing incline) at a constant gear, the engine will ...


24

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 more likely to be in its sweet spot with a 5-speed manual than a 4-speed automatic during regular operation. gear selection logic which was inferior to well-...


22

Holding the clutch in is generally not a good idea. The clutch is designed to be used for very short periods between gears, and for holding in first when you are about to pull away. So if you are wanting to coast you should definitely do it in neutral. The difference between these two from a fuel consumption perspective should be marginal. From a safety ...


21

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 actually) so they do not need to move around a lot of transmission fluid like traditional automatic transmissions do. Also they have a lot of gears (7, 8 or even 9 ...


18

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 from it. Something to remember about octane ratings is, the higher number does not mean it is more energy dense. The higher number indicates the fuel is actually ...


18

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 easiest way to get the job done in a typical consumer car. An A/C compressor actually takes a huge amount of energy to operate. In fact a central A/C unit for a ...


17

The ECON button is not a placebo, though the wording from that specific web page is a bit vague. The key is that the ECON button and the Eco-Assist system are two separate things. According to Honda, pressing the ECON button configures your car to improve mileage at the cost of performance. Turning it off will improve power and reduce mileage, which you ...


16

The root problem here is that you are conflating several different terms. See Wikipedia for a calculation of horsepower from torque (tau) and rpm (f in this equation): If you assumed a flat torque curve, you can see that peak horsepower would continue to increase with RPM. In fact, if you wanted to increase your marketing horsepower for a new vehicle, you'...


16

In a word: No. To add more to it: Absolutely Not. There is one huge thing which you have not taken into account. That being carbon which deposits from the air/fuel mixture burning process. Where does it go? Right into the oil (among other places). A small amount of blow by occurs which also forces this mixture down into the crank case. Now you have it in ...


14

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 is a manual transmission car. According to the car, the fuel consumption is nearly the same whether I downshift from fifth to fourth gear and let off the gas ...


13

Aside from financial and environmental considerations, U.S. and Canadian governmental agencies say that idling produces various negative effects on engine components. During idling engine does not work at its most efficient mode, and the fuel combustion is incomplete. That leads to glazing of combustion chamber and reducing effectiveness of spark plugs in ...


13

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 like 2.4kW which is about 8,000 BTU/h or about 3HP. So using an electric motor on a conventional car might give you a few more HP briefly, but the alternator has ...


12

As I said over here, mileage calculations are pretty easy: Fill your tank. Drive a well-known standard route. For example, my commute is almost always the same from day to day. Drive to gas station and re-fill the tank. Note amount filled and cost. Take the total miles driven from steps 1 - 3 and divide by the number of gallons filled in step 3. That's ...


12

This is an easy experiment to do: Fill your tank with unleaded. Drive a well-known standard route. For example, my commute is almost always the same from day to day. Drive to gas station and re-fill the tank with unleaded. Note amount filled and cost. Take the total miles driven from steps 1 - 3 and divide by the number of gallons filled in step 3. That'...


12

As you said the crux of the issue has to do with getting every last amount of energy out of a unit of fuel. You can consider this your total fuel efficiency. Accelerating your vehicle from rest to 60mph or 100km/h will require a fixed amount of energy based on the weight of the vehicle (excluding wind, friction and rolling resistance). So you need to ...


12

The most common causes (aside from poor driving habits) are bad timing bad sparkplugs low octane fuel* malfunctioning coolant temperature sensor blocked catalytic converter(s) malfunctioning MAP/MAF sensors driving with the parking brake engaged** having aftermarket wings on the car. tyres not inflated to the recommended pressure and a few others I can't ...


12

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 called fuel enrichment. It allows the engine to warm up and keep running, but at the expense of using more fuel to make it happen. When leaving the choke on for a ...


11

Any tyre design is a balance between cost, grip, longevity, water displacement and rolling resistance. Change one, and chances are you'll adversely affect the others... Personally, I would always put grip and water displacement (which affects wet grip) above all the others on a priority list. The difference between those "fuel efficient" tyres and normal ...


11

I think you need to define your terms. Efficiency could mean at least four things in this context: Least fuel consumed per hour. Most mileage covered per unit of fuel. Most kinetic energy created per unit of fuel consumed. Most acceleration created per second. These four choices often destructively interfere with each other. Hitting some of the high ...


11

As DucatiKiller notes, coasting downhill in neutral is usually considered unsafe, as it increases the chances of overheating your brakes. It is also illegal in many jurisdictions. Questions about driving techniques are generally off topic here, but you do have a question about how engines work that I think is (maybe marginally) appropriate: why do you get ...


11

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 computers with hundreds of sensors, etc. Also consider the size/power output of the engine. It looks like your car had a 4 speed manual. Most cars today ...


10

You are driving a Saturn S-Series (My car for the last 8 years, which I am very happy to have.) You should definitely have much higher fuel economy. (19.6mpg is what you have. 33+mpg is easily achieved.) I would hardly be surprised if it is the ECTS (engine coolant temperature sensor.) These plastic temperature gauges fail with about 100% certainty. This ...


10

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 would require roughly 10 hp at sea level to overcome the forces due to aerodynamic drag and maintain speed¹. The fact that an engine can produce 100 hp or 300 hp ...


10

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 in 8th. If you need more than half throttle, I would downshift.


10

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.


9

Your question has a few unconnected points in it: as jmosrt253 said, a Humvee engine is a large diesel engine - which means its torque is low down in the revs range Humvee engines, like many large diesels, are not highly tuned. They are built to be robust and survive in extreme conditions up to a point, horsepower is irrelevant for speeds. It is relevant ...


9

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 most cases 3 times or more a year. Ignition switches about twice a year, and fly wheels every 2 years. While you won't see this type of abuse,stuff will wear out. ...


9

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 goes off creating the combustion products and power. As the downstroke begins the pressure in the cylinder is high allowing the exhaust gases to escape and ...


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