Author Topic: What's wrong with my mileage?  (Read 6997 times)

BearDown

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What's wrong with my mileage?
« on: January 19, 2014, 09:06:42 PM »
I have a 2009 Hyundai GS and decided to try and get the best mileage I possibly could. I usually average around 28 MPG, which is what it's rated for, but I never watch my acceleration use, so I resolved to try as hard as I could to be stingy with the gas and just as stingy with the break after my last fuel-up. I'd coast to red lights, feather the gas pedal so I rarely used the break in normal traffic, never accelerate quickly at stop signs, roll down the sidestreet to my garage after work at a painfully slow speed, when all I wanted to do was punch the gas and get home as soon as possible, convince my wife to be easy with the gas by telling her this was another way to bring us closer to early retirement, etc.

Every time someone blew by me, I'd just tell myself, "Go ahead, waste your gas". Every time I'd miss a green light be seconds, knowing that I would have made it if I had been driving my regular speed of 5 miles over the speed limit, I'd calm myself down by imagining how much gas I was saving. Today was the first day I filled up since that last fuel up and I excitedly punched my mileage into Fuelly. What would it be? 30? 32? 34?







22.

22 freaking miles per gallon, easily the worse mileage I've ever gotten in this car. I almost wanted to cry. I've done everything I could possibly do and it's like my car is laughing at me. Does it actually get better mileage when I'm driving at higher speeds, regardless if I have to use the gas more, contrary to everything I've read here? Any tips would be appreciated.

Freckles

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Re: What's wrong with my mileage?
« Reply #1 on: January 19, 2014, 09:11:23 PM »
I don't know what's wrong, but I just want to say I'm sorry.  That's a sad little tale!

randymarsh

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Re: What's wrong with my mileage?
« Reply #2 on: January 19, 2014, 09:26:56 PM »
Good question. I have a similar issue with my Civic. It's rated for 25/36. In the summer I get around 31 driving what I would say is "normal". This winter I've gotten around 28 and we've had some very cold days.

When I drive for MPG, I can get 33 or so much but not much more. I got one tank at 37 but I'm not convinced the numbers were accurate.

I have read that while you don't want to have jack rabbit starts, you also don't want to take forever to get into the most efficient gear. You want to accelerate reasonably quick and steady.

Idling kills mileage, so missing lots of green lights may actually be bad. As far as efficiency (and not safety) is concerned, it makes sense to get through yellow lights.

Jamesqf

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Re: What's wrong with my mileage?
« Reply #3 on: January 19, 2014, 09:38:27 PM »
First question: how are you calculating your mpg?  Do you have an instantaneous mpg readout, or some sort of in-car display?  if not, you could be seeing the effect of an uneven fillup, or even have just a mistake entering numbers.

Beyond that, without knowing the particular car model I can't really say much.  When do you shift up?  Sometimes lugging the engine (under load) can be much less efficient than higher RPMs, but you really need an instantaneous readout to tell.

Greg

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Re: What's wrong with my mileage?
« Reply #4 on: January 19, 2014, 09:57:47 PM »
In some cars, coasting actually gets worse MPG than engine braking, since the ECU will shut off the fuel injectors when the throttle is closed above 2000 rpm, and then reactivate them below 2000 rpm.  Other factors are engine temp, as a cold engine can use up to 2x the fuel of a hot engine, and tires and brakes.
« Last Edit: January 20, 2014, 10:05:30 AM by Greg »

wtjbatman

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Re: What's wrong with my mileage?
« Reply #5 on: January 19, 2014, 10:31:05 PM »
Good question. I have a similar issue with my Civic. It's rated for 25/36. In the summer I get around 31 driving what I would say is "normal". This winter I've gotten around 28 and we've had some very cold days.

When I drive for MPG, I can get 33 or so much but not much more. I got one tank at 37 but I'm not convinced the numbers were accurate.

Wait. So your car should get between 25 and 36MPG, and you normally get 28 to 37MPG.

I wish I had your "issue" :D

randymarsh

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Re: What's wrong with my mileage?
« Reply #6 on: January 19, 2014, 11:26:04 PM »
Haha the "issue" I guess is that I can't seem to really beat EPA ratings on a consistent basis. Combined the EPA says 29, which I guess I beat but I do way more highway driving than city. Even my city driving is more like rural country roads with occasional stop signs.

Wanderer

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Re: What's wrong with my mileage?
« Reply #7 on: January 20, 2014, 07:50:25 AM »
Is this an automatic transmission?  I'm used to manual transmissions so I can give better advice there.  But I'd say if you were traveling the same route as usual, your car doesn't have a sudden undetected mechanical problem, your tires are inflated properly, etc., maybe you're going too slow.  Most cars prefer to operate in the 40-60 mph range, with no stops.  If you're spending a lot more time operating below 40 mph and getting caught at lights, that could decrease it.  I would say definitely creeping along through your neighborhood is lowering it, though it's good for not running over little kids! 

Nothlit

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Re: What's wrong with my mileage?
« Reply #8 on: January 20, 2014, 09:05:57 AM »
What was the weather like during these test periods? I've found that when it gets colder, my mileage drops even though my driving behavior remains unchanged. If your 22 MPG period was affected by the "polar vortex" or similar cold snap, I wouldn't be too surprised by that.

Spork

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Re: What's wrong with my mileage?
« Reply #9 on: January 20, 2014, 10:35:58 AM »

Gas quality can also affect mileage.  I know I lose 4-5% with the E90 gasoline.  You may have just gotten a bad tank of gas.

milla

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Re: What's wrong with my mileage?
« Reply #10 on: January 20, 2014, 11:08:21 AM »
My 14 yr old Toyota is now starting to consistently get 18 mpg. 18!!! He used to get 27-30. I don't know what's wrong with him but I don't wanna buy another one! 18 is minivan territory! I don't have any useful advice for you, just sympathy.

FastStache

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Re: What's wrong with my mileage?
« Reply #11 on: January 20, 2014, 11:15:06 AM »
My 14 yr old Toyota is now starting to consistently get 18 mpg. 18!!! He used to get 27-30. I don't know what's wrong with him but I don't wanna buy another one! 18 is minivan territory! I don't have any useful advice for you, just sympathy.

It's good to track your mileage, this could be a sign of a sensor on the its last leg, try replacing your O2 sensors.

milla

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Re: What's wrong with my mileage?
« Reply #12 on: January 20, 2014, 11:18:01 AM »
Always track the mileage, this was a sudden drop. Mechanic can't find anything wrong, O2 sensors have been replaced among other things. It's like he's losing the will to live...

N

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Re: What's wrong with my mileage?
« Reply #13 on: January 20, 2014, 11:25:05 AM »
maybe you miscalculated somehow?

my car gets 19...in the city. on highway, 33. and we 98% drive in the city.

Greg

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Re: What's wrong with my mileage?
« Reply #14 on: January 20, 2014, 11:31:32 AM »
My 14 yr old Toyota is now starting to consistently get 18 mpg. 18!!! He used to get 27-30. I don't know what's wrong with him but I don't wanna buy another one! 18 is minivan territory! I don't have any useful advice for you, just sympathy.

Your car should have OBDII or similar, and should be able to tell you what's wrong with it.  You may need a "code scanner" to find out what's wrong.  Some parts places will help you with this, in the hope of selling you the required parts.

Cromacster

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Re: What's wrong with my mileage?
« Reply #15 on: January 20, 2014, 12:04:42 PM »
Some Ideas to note:

First, its winter.  Your mpg for average commuting is going to be much worse for the fact its cold.  Of course I'm saying this assuming you are in a cold climate.

Every time someone blew by me, I'd just tell myself, "Go ahead, waste your gas". Every time I'd miss a green light be seconds, knowing that I would have made it if I had been driving my regular speed of 5 miles over the speed limit

Second, Its not necessarily the speed you are driving, but its the change in speed that really wastes gas.  I get the same MPG at a  steady 30mph and at 40 mpg (well I get 50 or so mpg at these speeds but my instantaneous gauge tops out at 50).  It would be my suggestion to go faster to make the light rather than miss it....You will waste alot more gas by stopping and starting than by speeding up slightly.  (This assumes you can time the light based on traffic flow and walk lights, and not just pure luck that it happens to change).

If you don't have the instantaneous read outs in your car, it might be worth picking up this

http://www.amazon.com/Newest-Bluetooth-Diagnostic-Scanner-Adapter/dp/B009F4JHHO/ref=sr_1_2?ie=UTF8&qid=1390244509&sr=8-2&keywords=bluetooth+odb2

Should work with your 2009 hyundai.  Syncs to your smartphone phone or otherwise bluetooth android/apple device.  A good app is called Torque, but others work as well.

https://play.google.com/store/apps/details?id=org.prowl.torque&hl=en

So for about $16 you can have instantaneous diagnostics, fault code recognition, some other cool stuff.

theSchmett

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Re: What's wrong with my mileage?
« Reply #16 on: January 20, 2014, 12:05:57 PM »
If the driving distance is equal and all that,

I would like to blame the winter blend gasoline, or maybe underinflated tires.

Also, maybe your next to last fill up wasn't complete, and your last fill up made up for the difference.

Try it again! Sciency types will say the experiment must be repeatable.

« Last Edit: January 21, 2014, 07:03:19 AM by theSchmett »

frugal_engineer

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Re: What's wrong with my mileage?
« Reply #17 on: January 21, 2014, 08:16:56 AM »
Every time someone blew by me, I'd just tell myself, "Go ahead, waste your gas". Every time I'd miss a green light be seconds, knowing that I would have made it if I had been driving my regular speed of 5 miles over the speed limit, I'd calm myself down by imagining how much gas I was saving.

Does it actually get better mileage when I'm driving at higher speeds, regardless if I have to use the gas more, contrary to everything I've read here? Any tips would be appreciated.

Driving slow does not result in better MPG!

All else being equal, going slower will net you WORSE mpg.  As mentioned above, in speed ranges less than say ~50 mph, the wind resistance is almost a non-factor.  Your car might need to make 30 HP to go 30 mph and 32 HP to go 45 mph in an idealized situation.  That means that by going slow, your car is burning almost the same amount of fuel and going less distance, resulting in lower MPG.

In fact, internal combustion engines are inherently less efficient when you are going slow!  The throttling of the air-flow into the engine reduces the thermal efficiency of an already inefficient machine.  The most efficient your engine will ever be is when it is at 100% wide open throttle.  While counter intuitive, there is an example of this principle in effect in little mopeds getting 150 mpg+.  They drive down the road pretty much pedal to the metal (or handle twisted as the case may be) which allows their engines to run at near maximum efficiency a lot of the time.

So, in short, the fact you were going slow and accelerating slowly was working against you in the mpg department.  You'll find that optimal mpg is attained when you find the right level of acceleration for your car, and it might be counter intuitively faster than you'd think, but more acceleration means you are letting your engine get closer to max efficiency.  The key is finding the balance that maximizes your vehicle.

exranger06

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Re: What's wrong with my mileage?
« Reply #18 on: January 21, 2014, 10:01:49 AM »
I can't believe no one has mentioned it yet...tire pressure. When was the last time you checked the tire pressure? It makes a huge difference in gas mileage. You might have gotten a nail in your tire and the pressure may have dropped because of it. Or it could just be because of the cold weather. Tire pressure is directly proportionate to temperature. The colder it gets, the more the pressure drops. I always have to add air to all my tires in the fall when it starts getting colder out, and come spring time, I have to let that air back out.

Or the pressure may be low because tires leak air. All tires. Every one of them. Doesn't matter what brand, size, or age they are, every tire ever made leaks air. So check your tire pressure at least once a month.

prodarwin

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Re: What's wrong with my mileage?
« Reply #19 on: January 21, 2014, 10:21:31 AM »
Wow, there is a lot of misinformation in this thread.

1)  22mpg sounds like an error in your instrumentation, calculation, or fill-up.  Repeat this over several tanks and look at your average.  I suggest tracking with something like fuelly.com

2)  Application of throttle isn't a bad thing, as long as you are using that energy.  As frugal engineer pointed out, higher throttle positions are more efficient.  If you use 25% throttle to get to 40mph cruise, or 60%, its unlikely that there will be any measurable difference.  Over 80% will bring many cars into open-loop mode, so it is not advised.

3)  Higher speed != better mpg.  Lower speed != better mpg either though.  In general, the efficiency sweet spot for many cars is going to be the slowest you can go in your highest gear (and not need to downshift frequently).  This is the point where you will get closest to the sweet spot in your BSFC curve with the least sustained road load.  In many cars I've driven, this ends up being around 30-40mph.  Extended periods of coasting while the engine is idling will waste fuel.

Some commutes lend themselves to hypermiling, some do not.  Some cars do, some do not. 

My Saturn averages around 30mpg (exactly 30.0 running avg. on fuelly currently).  Hypermiling without engine-off-coasting, and without interfering with the flow of traffic can sometimes get me as high as 32mpg.  Driving like an ass will bring it as low as 28-29mpg. 

My gen 1 Prius on the other hand...  drive it like a "normal" person to work, and I may get 42mpg.  Drive it with care and 55-60mpg is easily achieveable.  Drive it like my GF does (I can't figure this one out), and you can somehow get 36mpg.

grantmeaname

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Re: What's wrong with my mileage?
« Reply #20 on: January 21, 2014, 10:31:01 AM »
Are you taking short trips or combining them into longer ones?