Getting less MPG than what I am rated, whats the cause? - General

So I recently got a 5 speed 98' Chevy Metro, with about 160k miles on the car as a whole. However, the car had a new engine installed (its not aftermarket, its the standard engine the car was made for), a new clutch, radiator, etc. Was so new that the previous owner had the timing tuned down all the way so it could be broken in. When I bought the car, he instructed me to advance the timing about a quarter of an inch once I drove it 1500 miles or so and gave it some oil changes. Anyways, I was getting about 30MPG combined highway/city driving, which is understandable as the engine had the timing turned down to break it in. Now fast forward a bit and I put enough miles on it to feel secure to advance the timing to where it should be. I had it advanced a quarter of an inch but didn't notice anything really different so I ended up setting it to a third of an inch forward. However, my MPG is still fairly "low" for this vehicle, at around 34 MPG (33.8 to be exact). Considering its rated at 40MPG (45 highway [url]http://www.fueleconomy.gov/feg/noframes/14064.shtml[/url] ), what could be causing me to have 6-10 MPG than what it is rated? It is even more absurd to me as someone I know with an older automatic metro gets around 50MPG (who has the same body type as my car, I'm guessing its 97 or 96). Would the engine being relatively new cause worse MPG, even though the timing is advanced? Were his timing instructions not right (I'm afraid of advancing it too far, I don't want to damage anything)? I just need help in trying to figure out whats causing worse MPG here. The tires are properly inflated and all that, so that shouldn't be it.

Could simply be your right foot causing it

Its probably you, but EPA ratings are exaggerated.

I don't drive it too crazy or anything, unless going 65-70mph on a highway for half my miles on a 3cyl engine is enough to cut my milage by almost 10mpg or so :\

yeah that does seem like pretty poor gas mileage for a geo how fast are you accelerating, and how hard are you braking? also, try not exceeding 50 mph and see if that makes a difference because the faster you're going the more fuel you're using. you'll see a huge increase in gas mileage if you go 50 instead of 65-70.

I don't accelerate crazy fast often. The only time I do it is when I am working during rush hour, because its simply impossible to make a left hand turn on the street my job is located on unless I punch it. But that situation only accounts for a small fraction of the mileage I drive

are you cruising to stops and using engine braking instead of slamming on your brakes at the last second? decelerating very quickly also uses much more gas how fast are you going for most of your trip? if you really wanna get the best gas mileage then you don't want to go over 50-55

Could just be the car has higher mileage and needs a tune up. Or, how about where do you live? Do you live in a hilly area, or more flat? I live in Pennsylvania where before I had my 5.0 V8 my old 3.8 V6 Impala got better gas mileage than my Sisters 2.4 4cyl. because it takes more power (gas) for a car with not as much power to go up a large hill where I barely had to put my foot down in my 3.8. Gas mileage can be caused by so many factors. Is your catalytic converter partially clogged, or blocked? Especially on an older car. Taking the Catalytic out of my 5.0 V8 gave me 8 more miles to the gallon. (i wouldn't suggest it on a little metro as it needs more back pressure when a larger engine needs breathing room and exhaust flow) And to JDK, that's not exactly true. Going 50 may not get you better gas mileage than going 70. It all depends on the gear ratio of his car. My Caprice hits four gear around 70, therefore a drop in RPMs by almost a grand, instead of the RPMS being higher in third gear, even though I am going slower if I go a tad bit faster and up shift I'll get better fuel economy. It all depends on [B]each and every[/B] car though. It's up to him to find where his gears are in relation to speed. [editline]11th October 2011[/editline] Also, to the OP. Don't take this as an insult, but have you ever thought maybe you just aren't as efficient at driving a manual? When are you shifting each gear RPM wise? Do you *have* a tachometer in that car? I know a lot of older cars, even manuals do not have tacs..In which case I would really suggest buying one.

find a friend with a timing light and check your timing, just to be safe

[QUOTE=Halo0004;32721415]And to JDK, that's not exactly true. Going 50 may not get you better gas mileage than going 70.[/QUOTE] [citation needed]

Car doesn't have an RPM gauge but I'm 99% sure I'm shifting at the right times. To give you an idea of just how small my gear ratio is, I'm in 5th by 40mph if I'm cruising, (40 MPH in 4th gear audibly sounds at least to be 2000 - 2500 rpm). Fifth gear gets at about 2500 RPM or so at around 50MPH. Sadly, I can only take the highway to school (half of the miles at least on my tank) so going 50MPH on the highway isn't an option. On that note though, its not like I am flooring it either - often while highway driving I can easily just cruise by barely touching my pedal. If driving 65 on the highway is the cause I'd find that a little odd for small stuff like that causing me to lose almost 10MPG - doing the same behavior in my old accord would only nudge my MPG's 2-3 one way or another, if that (and thats an extreme). Like I said the engine is new, so would a newer engine cause worse MPG? It's got about 2000 miles broken into it, I figured it'd be good by now.

[QUOTE=KorJax;32723776]Car doesn't have an RPM gauge[/QUOTE] This is your problem. Buy and install an aftermarket one that straps to your steering column. It's not that hard/expensive.

You'll never get the book figures. Those figures are obtained in a lab on a rolling road. Real world conditions mean you can usually knock 10-15% off the book figure. Once the new engine has run in you'll see an improvement.

Temp has to do with it too in many cases.. there's a warmup time where it gets poor gas mileage no matter what. Then if it's cold out I usually see about a 3 -4 mpg drop on my oldsmobile. Plus factor in that if you're on the highway you'll be getting, say, 40... but on anything but the sideroad it will be drastically cut down. For example I get 28 on the highway @ 70mph @ 70*F (according to my info center thing).... so if the car was warmed up and I drove perpetually on the freeway I'd get 28. But in the end I end up around 24 or so mpg after I have to deal with the starting/ stopping / warm up of daily city driving. My city drive is pretty short compared to my highway, too... like 5 minutes city and 20 highway. Sounds about right probably.. you could spend money on little tweak to increase it slightly maybe, but probably best to say meh.. I would check the timing with a timing light, though.. just guessing while adjusting may have it a little off.

Try cleaning your MAF sensor and let your car idle for a few minutes before going anywhere to let the engine warm up.

How are you braking at lights? The instant I see a red light ahead of me, I let off the gas and just coast to a stop at the light. If it turns green before I reach it, I can gently accelerate back up to speed. It lets me get pretty decent MPG (21, car is rated at 23-25) despite driving it hard with the AC blasting on max pretty much constantly. [QUOTE=JDK721;32723025][citation needed][/QUOTE] Read the rest of his post.

I pretty much do the same, too. It's a little harder in this car though as I can't effectively engine brake due to the gear ratio being so tiny and if I just coast I take quite a while to lose my speed. Still, I don't really slam on my brakes or anything and when I'm working I know the area well enough to judge my timing at lights pretty well. And I don't think I need an RPM gauge. My old accord had one and I got pretty familar with it and what certain RPM levels sound like - I know when to shift audibly in other words. I'm sure I could get even better MPG if I had a calcuated way to accurately shift at just the right moment, but honestly I doubt small differences would cost 10MPG Anyways thanks for the input everyone. I'm pretty sure I just need to break the engine a little more and I'm pretty sure going 65-70 on a car that hits 5th gear at 40-45 for half the milage would easily cause less MPG too.

[QUOTE=sam.clarke;32726929]You'll never get the book figures.[/QUOTE] not true I easily exceed the EPA ratings for city and highway for my car [editline]11th October 2011[/editline] [QUOTE=Saber15;32730569]Read the rest of his post.[/QUOTE] you obviously don't know what [citation needed] means

maybe theres a cat stucki n the cat

[QUOTE=JDK721;32736344]not true I easily exceed the EPA ratings for city and highway for my car [editline]11th October 2011[/editline] you obviously don't know what [citation needed] means[/QUOTE] you don't need to cite physics, do you? low mechanical advantage = engine sacrifices torque but in turn, doesn't have to work as much