Use for questions related to fuel economy.

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17
votes
7answers
89k 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 ...
13
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 ...
12
votes
1answer
3k 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 ...
12
votes
1answer
8k 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 ...
11
votes
8answers
34k 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 ...
11
votes
6answers
12k 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 ...
11
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, ...
10
votes
13answers
60k 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 ...
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
2k 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 ...
9
votes
3answers
134 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 ...
9
votes
1answer
574 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 ...
8
votes
8answers
1k 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, ...
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 ...
8
votes
1answer
752 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
8k 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 ...
7
votes
5answers
270 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 ...
7
votes
5answers
5k 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
6answers
6k 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. ...
7
votes
1answer
2k 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
157 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
3answers
424 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 ...
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
18k 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 ...
6
votes
4answers
191 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
1answer
151 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
90 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 ...
6
votes
2answers
144 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
155 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
305 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
25 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 ...
6
votes
1answer
45 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 ...
5
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 ...
5
votes
3answers
4k 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 ...
5
votes
2answers
8k 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. ...
5
votes
2answers
313 views

Is manual start/stop good on older cars?

I have an old car (but with electronic injection) that predates by far start/stop systems which are used nowadays to save fuel (turning off the engine brings savings after 3-5 seconds, see Calculating ...
5
votes
2answers
361 views

When do engine type and mileage of a car affect pricing?

I'm currently designing a customer relationship management tool for auto shop owners and was wondering: Does engine type or the odometer value of a car ever affect pricing for a customer? What ...
5
votes
1answer
33 views

Fuel system question

See red arrow in the image. I place fuel additive in my car, all of the additives went into that pipe (in the red arrow image) because i didnt know how to place it. Will it still work? or just a ...
5
votes
2answers
56 views

What senses/controls how much fuel is spent for a given RPM?

When maintaining a constant speed on the highway whether up, down or flat the engine still has the same RPM (assuming the incline is shallow enough not to require a gear change) - common sense would ...
5
votes
1answer
53 views

2008 Toyota Corolla 141 Fuel Consumption Too High

I recently got a Toyota Corolla 141. The petrol consumption is too bad. It does only around 7.5-8 Km/l. Could you please let me know the reason behind this ? I was told that the vehicle is too heavy ...
5
votes
1answer
36 views

Why does my 2005 Mitsubishi Pajero use excessive amounts of fuel?

I have a Wagon with excessive fuel consumption. It's using 30 litres of petrol per 100 ks. I have seen many mechanics who can't find the problem. I know it has good intake and no exhaust problems. ...
5
votes
0answers
511 views

What causes more gas consumption - Idling with AC or Heat? [duplicate]

So I have begun doing some research on the effects of idling. So my question is, does idling with the AC or heater on affect how much gas is given off? If possible, please give the percent of extra ...
4
votes
5answers
7k 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 ...
4
votes
5answers
840 views

Can I save money using E85 in my flexible fuel vehicle?

Where E85 Ethanol is available (not very common), the price per gallon is often lower than regular unleaded gasoline. Though I've read that fuel economy is commonly reduced by 20% or more, when using ...
4
votes
2answers
759 views

How much improvement from replacing an O2 sensor?

I'm currently getting about 19.6 mpg city in my 97 Mazda Lantis 323 / Protege 1.8L. According to fuelly a car like this should be getting around 26 mpg. The car has about 127k miles on it, and I ...
4
votes
3answers
84 views

How would a bad barometric reading affect gas mileage?

My wife drives an '08 Hyundai Azera Limited 3.8L with ~79k miles. Over the past few months she has been complaining that the gas mileage has gone down. Normal around town driving was getting us ~19.6 ...
4
votes
5answers
35k views

What to check if fuel consumption is too high?

I think my car is consuming much more fuel than it should, I've compared it to other versions of the same model which have more powerful engines and mine seems to be on the higher end when is supposed ...
4
votes
3answers
12k views

Effect of loss of fuel tank vapours on mileage

Are there any estimates available on how much fuel you can expect to lose from a fuel tank that is leaking vapours? Leaking vapours would be caused by cracked/missing evaporative emissions hoses, a ...
4
votes
1answer
55 views

How is “Fuel consumption (economy) - combined” Calculated?

I have a Mazda - 323 S V (BA) - 1.8 i 16V (114 Hp) and the data sheet for it says: Fuel consumption (economy) - combined 7.9 l/100 km. How is this calculated and under what driving conditions?