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Discussion Starter · #1 ·
Hi guys,

Just wonderin -- I once remember doing a math problem that stated something I think there is some truth to it.

It said that for every mph over 60 , driving on the highway, you pay x amount more for gas than driving with a steady 60. Inother words, there is a certain speed on the highway that is most gas effective, or u run most miles with least gas.

I have a Nissan 92 Sentra XE, can anyone recommend or tell me what that speed for my car? I would greatly appreciate it .

(my gas mileage is horrible and have no money so I am trying to get the best out of it from my driving -- smooth accelaration, never step the gas pedal all the way to bottom, esp. immediately after a stop, etc.)
 

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Farms suck!
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Something's wrong with the car then. A GA16 should get great gas mileage no matter what speed you're cruising at. I suggest a tune-up and a fuel system inspection. As for the speed/mpg thing, I've heard that the ratio of rpm's/mph spreads apart more as you go faster. So technically, cruising in 5th gear at the highest speed possible(with light throttle) should get you the best mpg.
 

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Destroyer of worlds.
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there are many factors that go into the most efficient speed, for instance:

-wind direction
-wind speed
-barometric pressure
-tire inflation
-humidity
-ambient temperature
-road temperature
-number of passengers
-cruising gear ratio
-aerodynamics of vehicle (can change via owner and/or age)

the national highway commisioner has established that 55mph is the most efficient speed for most vehicles, and it seems to be about right. 55-65 is the most efficient unless you have unusual aerodynamics and gearing.
 

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well what he said... if you haven't tuned up in a while, go for it. new cap, rotor, wires, air filter, and plugs. NGK plugs are the best for these cars. don't get lured into the Bosch pit. the bosch supers aren't bad, but their platinum series are garbage in these cars. I have bosch wires and they're great.

also, I've noticed that if I drive the way I normally do -- taking each gear up before I shift, and doing 75-80 mph in the passing lane constantly, gas mileage isn't anything to brag about. but last week, as an experiment, I drove to and from my mom's house in maryland... about 60-70 miles each direction... keeping up with the speed limit, between 55-65. I made that round trip using less than a quarter tank. how you drive does make a difference. there's a couple other things you can try too. look in your owners manual where it says "economy hints" and has the upset car looking at money flying away.. there's a whole list of stuff you can do.

Dan
 

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also, get a good fuel injection cleaner. the chevron techron works decently, but it's a little pricey. the best I've used is the lucas fuel treatment. I love that stuff. pep boys, advance, auto zone, etc, should carry it. I haven't seen much improvement from the lower priced brands, but maybe someone else has, so I'm not gonna rule them out. but the lucas works fantastic.

Dan
 

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Discussion Starter · #6 ·
Well, to be honest havent done much tune up -- I have just changed to NGK sparks, wires holding them seem to be fine.

My gas.mileage drop during the past few months seems to be, as weird as it may sound, it happened before the winter started when I put one of those liquids u put in the gas tank to mix with the fuel to do some cleaning of the system. I put one of those and eversince them, is it the cleaner, is it the winter, is it the tune up .. I dont know but my gas mileage dropped .. and 20 mpg for city driving is not really what im happy about. At the same time I cant afford to take it to a shop cuz I just got the news I got in to George Washington for Masters and the basterds are giving me only 1/3 tuition. So I have to save every damn penny to pay the tuition and living expenses in DC.
 

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dude that's a blow. I know how that is.

but 20 mpg is awful for a GA motor. even if it's never been tuned up, it shouldn't be that bad. does it run smooth? does it idle ok, or does it seem to fluctuate or idle high? does it sputter, buck, or jump?

you might want to check your timing. but first, I'd be checking for a gas leak somewhere. check the lines at the filter on the firewall, and at the fuel rail. then climb under the trunk and check the hose connections for leakage. I had to replace a dryrotted fuel line that was dripping. for a multiport injected engine, especially the GA, you've got a problem if you're getting 20 to the gallon. I'd check for a gas leak.

Dan
 

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Discussion Starter · #8 ·
It runs perfecly smooth -- never had any doubts somthing does not feel right. Never jumps, nver anything. Its just that gas mileage. Everytime I getoff the car I look around the tires, in the back at the exhaust -- seems dry and no leak.

I do not know to tell u if it idles "OK" or "high" ...

I am gonna ask someone to look over it but the problem is that hes doing that all the time for his friends and he does not get any rest, so lately he's been rejecting anybody calling him to fix their car -- u know how it is if u r the mechanic of the local community :)
 

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Lowest fuel consumption per mile traveled is generally that speed at which rolling resistance and aerodynamic resistance are equal. This assumes tallest gear available.

This is modified to some extent by the torque curve and gearing.

As a rule of thumb, the crossing point is between 50 and 60 mph. That's why DOT set speed limit at 55 mph in the Dark Ages of the two "Fuel Crises".
 
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