Hot answers tagged

18

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 ...


17

Lean ≠ More Air I believe the source of the misunderstanding is in how the term "lean" is being interpreted. A lean mixture doesn't indicate the presence of more air. It indicates the presence of a higher proportion of air compared to fuel (air-fuel ratio, or AFR). Quick example Mixture A has 1,000 g of air, 80 g of fuel. AFR = 1000/80 = 12.5 ...


14

letting the car idle isn't good for the car, especially with the AC on. What you're basically accomplishing is aiding in the car wearing without racking up any miles. With the cylinders firing, you are using several electrical components, putting some small amount of stress on the belts, etc. If you've ever seen ads for cars claiming high mileage but ...


14

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, ...


13

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 ...


12

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 ...


10

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 ...


10

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. ...


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 ...


9

The key things you can to to keep your fuel economy: Keep it tuned up: for spark plugs and wires, go with the manufacturer recommended brands/default ranges. Additionally, you'll want to make sure you change the oil regularly, as sludgy oil will rob your motor of efficiency. Finally, a clean air and fuel filter will also go a long way to imrpoving fuel ...


9

No, the tachometer can not be related to fuel efficiency as the tachometer is measuring the amount of rotations per minute (RPMs) of the engine. In the same gear and at the same speed your tachometer will always be at the same RPMs. However, you can be at 2000 RPMs and be barely touching the gas pedal (or completely off of it) because you are coasting down ...


9

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 ...


9

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 ...


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

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 ...


9

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 ...


9

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 ...


8

The short answer is that yes, you can change your differential to optimize fuel efficiency. CAVEAT: it is almost certainly not worth it. Here's a very high level discussion of why there are better ways to achieve the same goal (better fuel efficiency): Think about how the air-fuel mixture in the engine is managed: for each revolution of the engine, a unit ...


8

Yes, gear ratios are the second largest influence on your fuel consumption. Number one being maladjusted timing. I always relay the story of my and my wife's cars: she has a 1.4 Opel Corsa and I have a 2.0 Turbo Coupe. While my car has more than twice the power of hers and weighs 350kg more, we get about the same consumption figures (she gets 12.5km/l and I ...


8

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 on the crude that went into the refinery and the processes the refiner has at hand to process it. Refineries vary in there capabilities. There are over 60 ...


8

It's not that the catalytic converter can't handle more air per se, it's that running lean increases the temperature of combustion (I actually don't know why, but now I'm curious) and the catalytic converter needs to run inside it's chemical operating range. Something to do with the chemistry that I also don't know. As for advantages for turbo boost and ...


7

Some good points have been given already especially as far correct spark plugs and correct fuel go. Some other points, unfortunately, I can only describe as regurgitated 'car-care' sales drivel. I'm almost surprised that no one has mentioned that you should wax your car more often. Here is a list of things that are not worth your money and time: Changing ...


7

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 ...


7

With regular driving the Air/Fuel ratio is kept constant at 14.7:1. So if a larger engine needs more air (more swept volume) per cycle then yes it will require more fuel. So the question boils down to which engine has more friction per cycle, and which car has more weight to carry around. The friction is measured in FMEP (friction mean effective pressure) ...


7

tl;dr: Ambient air temperature should generally not interfere with engine efficiency or fuel consumption, but will affect overall power output. Do not confuse efficiency with power output. These are two separate things. When your intake charge is more dense, you can throw more fuel at it and creates more power. (NOTE: The idea for the engine management ...


7

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. ...


7

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 energy, this uses energy. Rolling resistance. Although tires eliminate friction, there is little rolling resistance that converts kinetic energy to heat when ...


6

This is more complicated than a simple ratio. I present as evidence exhibit A: the comparison between the BMW M3 and the Toyota Prius on the Top Gear test track. In short, the Prius was driven at its top (not very high) speed and the M3 remained right behind it for ten laps. The resulting fuel economy results were: 17.2 mpg Prius 19.4 mpg M3 That's ...


6

As a bald indication without other context, no, the tachometer is insufficient to tell you much about fuel efficiency. Your trip odometer and fuel gauge are your only truly useful (and built-in) measures. Reset the trip after a fill-up and make a mental note of when you hit the 3/4, 1/2 and 1/4 marks on the fuel gauge. While the fuel gauge might not ...


6

It is possible that you have a brake or brakes that are dragging. After a 15 or 20 minute drive stop the car and check for a sticking caliper. Feel each wheel in the area of the lug nuts to see if one feels much warmer than the others. They should all feel warm but about the same temp when comparing both backs and both fronts.



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