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What is your fuel economy and how to improve it?

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December 9, 2011 4:21:59 AM

Ok, 1999 Mazda 121 (Demio) Metro is suppose to have fuel economy of like 7L/100km from manufacturer. But I am getting something like 13L/100km. The car has about 90000km on it. Is this normal? I don't think it is and what could possibly be causing this? Is it my driving behaviour or do you think there is something wrong with it mechanically and how can I tell?

Also it would be interesting to know what is the actual fuel economy of your car (not the one reported by the manufacturer). Tips on how to save fuel are welcome.

More about : fuel economy improve

December 9, 2011 9:20:30 AM

Maruti is not available in my country (Australia).

I don't speed.

Can't be easy on the throttle (don't want to drive like old people). But I will try.

Can't do that. Traffic in my area does not stop long enough for a real stop/start. It will probably deplete my battery and people will kill me (road rage).

Already have a mechanic looking after the car every so often (scheduled maintenance after certain number of km).

Can't do that, I am driving myself only and ok may be I am overweight, I am by no mean very heavy (75kg).

December 10, 2011 12:11:01 AM

I have an '02 Dodge Durango so i get about 16.8 mpg (14 L/100km) on a normal week, good weeks with no traffic on the highway its about 17.2 mpg (13.6 L/100km).

One thing to keep in mind is that stop and go really kills the gas milage so if its possible to find a route between home and work with fewer traffic lights, even if its a bit longer, it can lead to a decent change in gas mileage which could add up to make a difference depending on how far out of your way it is and how much gas is for you.

You also dont necessarily have to be light on the throttle, just be smooth with your acceleration, if your car is shooting up to a high RPM to get you off the line then dropping significantly once you are up to speed you could probably smooth it out so it stays at a more moderate RPM during your acceleration and this can help a fair amount. I have an hour commute to work and have played with this theory over a few weeks and it did help a small bit, but its also a fun game to keep me entertained so its not super scientific and your results may vary, but when you are getting really low gas mileage a 0.2 MPG improvement actually adds up over several weeks.


Depending on your regular drive and how patient you are, mythbusters did show that following about 100 ft behind a semi truck gave about an 11% boost in their gas mileage so if you really want good mileage you can follow a big truck to work and it should help a fair amount.


Question for those of you on the metric system, whats the equivalent word for mileage or do you all just use fuel economy instead?
Related resources
December 10, 2011 1:28:37 PM

I will see if I can find a route with less traffic lights. The dashboard does not have the rpm on it, I will just have to listen to guess if I am on high rpm or not. Yeah I tend to accelerate fast and reach the speed limit and let the foot go.

Following a truck? I overtake them. I also don't think there is enough truck to follow for the entire trip.

Yes, I think you can express fuel economy in 7L/100km or in 14.3km/L. I perfer 14.3km/L but looks like car website express them as L/100km. Milage is just strange considering metric use meter not mile (meterage??).
December 12, 2011 7:26:39 PM

Maintain an even speed and stop tromping on the gas. Using fuel injector cleaner can help if you have never used it.

I get 26mpg on average in my 2010 m3 2.5L. And i tromp on it.
December 12, 2011 8:25:16 PM

How do you use fuel injection cleaner?
December 13, 2011 11:39:48 AM

It comes in a bottle you add to your gas tank every so often. Any auto store and most chain stores like an eu version of walmart should have it. It cleans any build up. Its also good to open up on the throttle once in awhile [high rpm spirited driving] as it helps do the same.

If you still get horrible gas mileage after driving like a granny and following our tips then perhaps its an issue with your car. Hard to tell without many more tests though.
December 13, 2011 9:03:32 PM

According to your initial comments you should be getting somewhere around 33.6MPG (factory specs) and you're getting around 18MPG.. That represents a 46% decrease in fuel efficiency which in my opinion will not get better with any injector cleaner. The cause could be any of the OBD-II sensors or as simple as the air filter… but you will not know exactly which is the cause without getting it on the computer or at least reading the OBD-II computer codes… AutoZone is know to have that service available to their consumers, and that company must be available in AU, so take your car to an AutoZone auto parts dealer and ask them for a computer code extraction, they will use a portable OBD-II scanner that according to the code readout should produce the faulty sensor or cause. And if AutoZone is not available in your area ask your mechanic to use an OBD-II scanner. The likely sensor at fault may be the Oxygen Sensor but without a computer readout it would be guesswork and possibly a waste of money.
December 13, 2011 11:42:49 PM

Thank you Chicano. I will see where I can find mechanics with a scanner. Do you think an engine specialist will be able to check it?
December 14, 2011 12:21:31 AM

Yes I do think so... a basic scanner as far as I know is around $90 US dolars so any mechanic should afford at least a basic scanner. Good luck!!
December 14, 2011 12:46:33 AM

A basic scanner is pretty cheap to get. Your throttle body could be sticking a bit as well. Like Chicano said a sensor can also be doing that but you would most likely get a check engine light on if that was the issue. At 90000km you might have bad spark plugs or spark plug cables if your car has them. A plugged air filter will drastically reduce your fuel economy as well. Does your car have a rough idle when you start it or does it run smooth? A 46% decrease in fuel economy is big so it would be good to know if you have noticed anything else at all.
December 14, 2011 1:03:29 AM

Didn't notice any rough idle. Will check spark plug and air filter.

One thing I notice is that sometimes after I stop the car and my foot is on the brake, the brake resistance (how hard it push against my feet) drops a bit. It builds up again after I step on the accelerator. Is this normal?
December 14, 2011 1:34:38 AM

wip99gt said:
Like Chicano said a sensor can also be doing that but you would most likely get a check engine light on if that was the issue.
You're right about that.. the check engine light thing just skipped my mind... may be because I've never had a check engine light turn on.. but Pyree didn't mention it either when it's obvious it should be on with the mileage it's getting, so who's to say if the Check Engine light is working correctly?..
December 14, 2011 1:52:47 AM

I am sure the check engine light is not on, that's why I did't mention it. I would call the RAA (roadside assistance service) if the engine light is on while driving.
December 14, 2011 4:23:22 AM

That's strange because at the mileage it's getting, the computer should detect something is wrong and send a check engine light warning. Maybe the codes will show something even if the light doesn’t turn on. As you can see here, the light should turn on even for minor problems so more the reason it should be turned on in your car.

What you mentioned about the brake pedal loosing pressure, that may indicate the power brake booster has a leak… that can cause an engine vacuum leak below the throttle body that may cause the engine to idle at higher than normal rpms, and possibly waste fuel. If the computer compensates for the additional fresh air injecting more fuel, that may be the cause for your lowered mileage. If you had a tachometer in the dashboard you would be able to tell if it’s idling higher than normal but if your transmission is automatic, you can tell if the rpms are high as follows: When you come to a stop sign on a level street, put the shift lever in neutral, then without touching the gas pedal, release the brake pedal, and shift the lever into D (drive),.. if the idle is normal, the car should start crawling slowly to equal the speed of a slow walking pace.. but if the idle is higher than normal, it would start moving faster to equal a faster walking pace... if this happens, that may explain the high rate of fuel consumption. Whatever the results, have your brake booster checked and computer codes read, and you can check the codes here
December 14, 2011 11:51:56 PM

Good call on the brake booster chicano. I have seen some large industrial diesels that have had codes that were not present on the screen so like he had stated the check engine light not being on does not mean there are no codes. It's just rare when that happens.
December 15, 2011 3:14:37 AM

wip99gt said:
Good call on the brake booster chicano. I have seen some large industrial diesels that have had codes that were not present on the screen so like he had stated the check engine light not being on does not mean there are no codes. It's just rare when that happens.
Thanks wip99gt... Sounds obvious there should be a check engine light... if they turn on for small issues, why not for this one,.. right? Maybe the bulb is blown if it even uses an incandescent bulb... a LED would be more durable.. infact I've never known of a blown LED so who knows what goes on.
December 15, 2011 11:03:42 PM

I have seen wires short out in dashes before, never for a check engine light though. Of course whenever I say it could never happen I'm proven wrong.
December 20, 2011 11:56:56 PM

RXP if you can find it burns the carbon in the engine and restores performance and slightly helps gas mileage.
Dave
December 26, 2011 4:28:03 AM

Emptied the fuel again and do another run, and getting fuel from another service station. This time I am getting 9-10L/100km (specification is 9L/100km driving in the city). Maybe the fuel from the other station is dodgy?
December 26, 2011 8:59:06 AM


One of the options on my car is to be able to see the current average and although it's a bit mesmeric watching it when you're driving, it does throw up some interesting reading. For instance, I can start off from a roundabout doing 8.9 to the gallon and get up to 23 then by lifting my foot slightly and without losing any speed, I can leap to forty five or more. Braking down to the next roundabout increases to a doubtful 99.9 but overall, by using lighter right foot, I've got my tank average up from 21.5 to 23.4 and with petrol (including over 70% tax) in the UK being over £6 a gallon, that's a start.

I'm mostly local journeys of less than ten miles and may three or four of those a day. I'm sure if I did longer runs I could get up to almost thirty and for a 4litre V8 pulling nearly two tons, that ain't bad!


December 26, 2011 10:48:33 PM

Pyree said:
Ok, 1999 Mazda 121 (Demio) Metro is suppose to have fuel economy of like 7L/100km from manufacturer. But I am getting something like 13L/100km. The car has about 90000km on it. Is this normal? I don't think it is and what could possibly be causing this? Is it my driving behaviour or do you think there is something wrong with it mechanically and how can I tell?

Also it would be interesting to know what is the actual fuel economy of your car (not the one reported by the manufacturer). Tips on how to save fuel are welcome.


Good simple ways to increase fuel economy:

Accelerate slower...instead of nailing the gas once the light turns green, take it easy, let your car roll and once it gets moving well, then start you start giving it gas.

Don't gas it on hills. If you see you are about to get onto a hill, give it lots of gas before you enter the hill.

Don't carry loads of crap in your trunk. It won't save much, but penny's do count.

A huge one is keeping your tires properly inflated, don't neglect that.

Here are some BIG NO-NO's

-If you drive a manual, don't shift up your gears to keep your engine at low rpm's. You think this saves you gas, but it doesn't. Infact, the engine has far more load on it which kills it eventually and you have to give it more gas to keep accelerating. For your and your engine's best interests, keep the rpm's higher rather then lower when in doubt.

-Do not shut your engine down when stopped. When you shut-down and and turn it back on, your entire array of electronics, starter, cooling system and such must all stop and restart...they have a very limited amount of times that they can be used. It may save you insignificant amounts of gas, but you'll have to replace all of those parts sooner which costs thousands.
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