Use for questions related to fuel economy.

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26
votes
6answers
6k views

Do cars consume less fuel when in Neutral? [duplicate]

Imagine we're going down a hill and we're driving a manual car. There are two situations: If I put my car in neutral it will go downhill without any need for the injector to squirt fuel into the ...
20
votes
6answers
1k views

Will higher octane fuel improve towing power?

According to Will higher octane fuel improve gas mileage? higher octane fuel does NOT notably improve fuel efficiency. Will higher octane fuel, increase power while towing? I looked online and ...
19
votes
7answers
125k views

Is idling bad for your engine?

If I sit in my car for 30-40 minutes with the AC and the car idling, does that "hurt" the engine, or does it simply waste gas and pollute the air? Would it be better if I turned off the car? A ...
15
votes
6answers
2k views

Why or why not increase engine efficiency by running the car “fuel-lean” (using a turbo or supercharger)?

Everyone wants their cars to use less fuel, right? I read the following passage about running the car fuel lean from this website: Run the engine fuel-lean, that is, use excess air. It is well ...
15
votes
8answers
69k views

What can cause a car to consume more fuel?

All over my long driver career, I had 4 cars (5 years). I always compare my fuel consumption with other people who have the same car. 3 times out of 4, I found out that my cars were consuming more ...
15
votes
4answers
1k views

What makes two-stroke engines less fuel-efficient than four-strokes?

It is a commonly-held belief that two-stroke engines are less fuel-efficient than four-stroke engines, and some example BSFC figures appear to confirm this as well. But what is it that causes two-...
15
votes
3answers
1k views

Are there any advantages of idling a vehicle vs. turning it off and back on again?

I was sitting outside, eating my lunch the other day, and a small bus (you know, one of the short ones) pulled up to the sandwich shop I was eating at. I noticed that the driver got out of the bus, ...
14
votes
6answers
14k views

How to improve fuel economy in high-mileage car?

I'm driving an 2003 Acura TL 3.2 with 177K miles on it. I bought the car with 110K miles on it. It seems to me that the car is not getting the same fuel economy that it did when I acquired it. I ...
13
votes
1answer
4k views

how to optimize fuel consumption by changing the rear differential ratio?

Is it possible to improve the fuel consumption (decrease it) in my van by changing the rear differential ratio? I would like to optimize it for low-speed driving about 40 km/h (25 mph). Is it true ...
13
votes
2answers
18k views

How much does spark plug gap affect fuel efficiency?

I've read conflicting reports regarding how plug gap can affect fuel efficiency. For example, I've read that too small a gap won't cause a clean burn, or that too large a gap can cause misfires due ...
12
votes
2answers
5k views

How does ambient temperature affect engine efficiency and fuel consumption?

I remember from my physics class that the ideal-gas Carnot engine is more efficient if the temperature difference between the heat source and the thermostat ("heat recipient") is larger (http://...
11
votes
13answers
99k views

Is the ECON button just a placebo?

I recently bought a Honda Civic that had this in the car: I have no idea what it does, and how it's supposed to help. Even Honda's website is ambiguous, just using a lot of fuzzy words to describe ...
11
votes
8answers
2k views

Is shifting to neutral on a decline more fuel efficient than keeping the gear engaged?

I always had the habit of shifting to neutral on long declines and using the brakes to slow down as needed. Intuition made me believe I'd be saving fuel as opposed to keeping a gear engaged. However, ...
11
votes
1answer
743 views

Brake Specific Fuel Consumption of 2-stroke vs 4-stroke

How much fuel do various types of engines burn per power output? I'm especially interested in naturally aspirated piston engines, and comparing two-stroke to four-stroke. The wikipedia article gives ...
10
votes
6answers
2k views

Can a car AC unit be run on just the car battery?

This might be a silly question but I was wondering if a car AC unit be run off entirely on battery or alternator? As this could help in Preventing power loss during important times such as ...
10
votes
2answers
2k views

Pulsar 180 - How Can I Measure the Mileage?

Could anybody please tell me how to measure the mileage of my Pulsar 180 bike accurately? I have tried by emptying my tank. I failed miserably, and I had to take my bike walking long distance.
10
votes
2answers
309 views

40MPG at 100MPH?

Around 1987-1988 I had a Ford Fiesta/Festiva. I was in the Army and regularly made weekend trips, driving from southern California to Central Washington a trip of about 1200 miles. I would leave in ...
9
votes
6answers
663 views

Fuel consumption at same speed of different engine

I am wondering why two car running at 100 km/h for example with a 100 hp consume less fuel that an engine of 300hp. Even if I take a supercar lighter and more aerodynamics it will consume more. But ...
9
votes
1answer
246 views

Does leaving the choke closed increase fuel consumption

I ran out of fuel using my outboard engine the other day, when I had checked the tank beforehand and thought I saw plenty of fuel. I had forgotten to open the choke for twenty minutes or so. My ...
8
votes
3answers
22k views

Engine Size and Fuel Consumption

I have this weird misconception that the engine size is related to the amount of fuel being burned in one cycle(4-stroke engine). I know this is stupid but how does engine size relate to the amount of ...
8
votes
2answers
13k views

Is topping up the oil enough of an oil change?

If you use synthetic ester-based oil in a relatively new petrol engine, top it up regularly, and the engine runs very quietly and basically without any noise whatsoever (especially after another top ...
8
votes
2answers
798 views

For how long should I idle at a stop?

As I approach a stretch of road that has been single-laned due to roadworks, the sign-flipper spins the sign to STOP. Having been through these roadworks before, I know I'll probably be waiting at ...
8
votes
7answers
8k views

Fuel efficiency and Shifting/RPM

I was reading a thread in a car forum where someone wrote: The lower the RPM, the less fuel you use, the less strain you put on everything.. Another person then replied, stating: Not true. ...
8
votes
3answers
5k views

Does accelerating faster worsen fuel efficiency?

I've often heard that accelerating harder makes for bad fuel efficiency, but have yet to be given a sound explanation of why. Naturally this makes me question this advice. Now obviously when you ...
8
votes
2answers
3k views

Low power, bad gas mileage, smelly exhaust after engine work

My 92 Civic has had low power (need to use at least one gear lower than usual to get the same power) and has been getting bad gas mileage (15-25mpg vs 32-42 mpg usual) since I replaced the head gasket....
8
votes
1answer
791 views

how can I measure the amount of fuel injected into a diesel engine in real time in a purely mechanic pre-OBD vehicle?

This is a Mercedes-Benz 308D van, year 1992, model 602.316. Pre-OBD, no electronics of any sort, everything is purely mechanical. I would like to retrofit a system which would measure the precise ...
7
votes
4answers
2k views

why do engines have so much unused horsepower?

I've looked at the power rating of an engine used in a Humvee (5500 lbs) and was surprised it's only ~190 horsepower, which is exceeded by many 4 door sedans. So an obvious question is why doesn't my ...
7
votes
2answers
116 views

Driving slower at low constant rpms or driving fast to get to destination faster, which saves more gas?

As the question title says. I am a new driver and I understand that driving at higher RPMs can burn more gas faster. However getting to a destination longer would mean you were spending gas at a ...
7
votes
5answers
7k views

Can I improve fuel economy by changing differential’s gear ratio?

I would like to use my Lada Niva for normal road travel, but at 3500 rpm at 100 kph it is not very fuel efficient. I don’t know what the current differential ratio is, but I assume it has been changed ...
7
votes
3answers
197 views

Will an old engine have worse fuel efficiency than a new engine?

I have a gasoline-engine car that is four and half years old and has been driven for 60 000 kilometers. I have noticed that the fuel efficiency is not what it was when the car was new. However, I ...
7
votes
1answer
4k views

What does a healthy spark plug look like?

The spark plug pictured here: Has some black carbon on the underside of the ground electrode and has black carbon on the "base" area below the centre electrode (not pictured). Is this normal and ...
7
votes
3answers
177 views

Gas mileage down significantly the last few tanks: what should I look for?

The gas mileage in my car is degraded significantly the last three tanks. What should I look for? Details of the vehicle are below, but this question could also apply to anyone who sees this problem ...
7
votes
1answer
55 views

Gasoline grade manufacturer recommends vs what was used during testing

Toyota recommends to use regular(87) grade of gasoline, but tested cars with the gasoline grade 91(see user manual). Somebody know why they recommend to use grade 87 if they did not tested cars with ...
7
votes
3answers
763 views

Calculating MPG from MAP sensor (or converting MAP data to MAF data)

My 2002 Honda Accord V6 has a Manifold Absolute Pressure sensor (MAP). I understand that this sensor gives out information in pressure units (psi or equivalent). After doing a bit of research, I ...
7
votes
0answers
115 views

fuel consumption is high

My VW Golf 3 is over-consuming fuel, I use 10 liters for 45km, My mechanic ask me to change the automatic gear-box because it is not selecting gear above gear 3 I change the automatic gear-box but ...
6
votes
5answers
8k views

How to save fuel on downhill slopes on a motorcycle: clutch or neutral?

I have a two wheeler i.e. bike (Honda company, four stroke) which has four gear. While driving my bike, when I come to downhill slopes, I shift the motorcycle to neutral to save the fuel. (The slopes ...
6
votes
4answers
2k views

Does the tachometer provide any indication of fuel usage?

So, I'm driving along on the highway with the A/C blasting when I notice the price of gas. It makes me think, "what can I do to increase my fuel efficiency?" Some of the tips I've heard have included ...
6
votes
4answers
1k views

Are there any disadvantage to fuel efficient tires?

I'm in need of new tires and I saw some fuel efficient/low rolling resistance tires. Is there any disadvantage to this type of tire?
6
votes
2answers
120 views

Does starting and stopping the engine lots over a short period of time in a non start-stop car damage anything? [duplicate]

In my 2003 Opel Agila 1.2, I try to save fuel and stop the engine manually (by turning the key) when in traffic or waiting at traffic lights etc. Sometimes when in traffic I can stop and start my ...
6
votes
3answers
250 views

Tapping into the on-board computer

I'm thinking of replacing my car's radio panel with a custom built Raspberry Pi device, something like this device. However, it's usefulness would be much larger, if I could get information from the ...
6
votes
4answers
234 views

Cheap vs Expensive Fuels [closed]

What is the difference between the cheapest fuels in a place like Tesco's and the 'high quality', highly priced competitors? Is there actually any noticeable difference in available power, engine ...
6
votes
3answers
434 views

Does Max Power RPM Equal Max FE?

I was looking over the specs for a 98 Mazda 626 2L and noticed that it says the max power is at 5500 RPM. Will the Max Power RPM also be the RPM at which the engine is most efficient assuming you'...
6
votes
2answers
9k views

Why does my engine perform poorly and get bad gas mileage after using fuel injector cleaner?

At the advice of someone at a local auto parts shop, I poured a bottle of fuel injector cleaner into my gas tank. This happened around the same time that I had a brake job done and rotated my tires. ...
6
votes
1answer
191 views

Why vehicles use fuel and how can fuel economy be improved?

Why vehicles use fuel? Where does the energy in the fuel go? Vehicle fuel efficiency is continuously increasing. Why is this the case? What technologies car manufacturers are using to improve fuel ...
6
votes
3answers
222 views

Optimal acceleration for automatic transmission? [closed]

In a car with automatic transmission, what's the best way to accelerate so as to minimize fuel consumption? Assume I'm not going to change the gears manually. Note that I'm also considering non-flat ...
6
votes
2answers
374 views

How to find the cause of sudden high fuel consumption of a motorbike?

About my bike Model: Honda CBR 250R Total Run: 35000kms Total Time: 2 years 3 months Clutch Plate changed at 30k kms after an accident Engine oil, engine oil filter and air filter changed in ...
6
votes
1answer
513 views

Oily Sludge in the Intake Manifold

When taking off the throttle body to clean my IAC, I noticed that there was a thick layer of oily sludge coating pretty much everything inside the intake manifold: I have two queastions: How did ...
6
votes
1answer
184 views

Alternative fuel consumption metric to MPG to measure actual engine efficiency?

MPG is all very well and good, considering that most people that are concerned about their fuel consumption tend to want to get as many miles as they can out of it before they need to fill up again. ...
6
votes
1answer
48 views

1967 Ford F100 miles per gallon

I plan on getting an 1967 ford f100 and saw that the gas mileage isn't the best on these trucks. The certain truck I have my eye on has a V8 5.8L engine and was wondering if more liters in the engine ...
5
votes
3answers
730 views

For 2 identical car models, 1 being cabriolet, which consumes less fuel?

What is the effect on car fuel consumption of having a roof or not? I guess it may depend on the car model, but generally, considering common commercial cars, which setting saves more fuel?