Sudden, Drastic Drop in MPG - Nissan Forum
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#1 Old Aug 23rd, 2005, 08:21 AM
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Sudden, Drastic Drop in MPG

Does anyone have any ideas on what would cause a sudden, drastic decrease in gas mileage, by 5-10mpg?

Air filter is clean, oil changed recently, tire pressure is good.

My mileage just tanked from ~35mpg on premium to ~28mpg on premium, worse on normal gas.

My knowledge is not the greatest when it comes to car maintenance, so any ideas on what else to check?
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#2 Old Aug 23rd, 2005, 08:29 AM
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If its so abrupt then it's probably more than a comman maintanice problem, for instance it could be your injectors, but they only slowly clog over time. Get some fuel system cleaner just in case though.
#3 Old Aug 23rd, 2005, 10:38 AM
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Quote:
Originally Posted by jreese86
Does anyone have any ideas on what would cause a sudden, drastic decrease in gas mileage, by 5-10mpg?

Air filter is clean, oil changed recently, tire pressure is good.

My mileage just tanked from ~35mpg on premium to ~28mpg on premium, worse on normal gas.

My knowledge is not the greatest when it comes to car maintenance, so any ideas on what else to check?
Did you break in the car? Im betting no.

Also could be the quality of the gas.

Quote:
Originally Posted by muchachomaloo
Ok... maybe I am just retarded then :(.

^^ The truth finally comes out.
#4 Old Aug 23rd, 2005, 10:41 AM
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Quote:
Originally Posted by Flying V
Did you break in the car? Im betting no.

Also could be the quality of the gas.
I bought it used, so I don't know if it got broke in or not.

The bad gas mileage has spanned over the last 4 tanks of gas, all pumped at different places. I usually run it down damn near empty, so if it was bad gas, it should be gone for the most part.
#5 Old Aug 23rd, 2005, 10:50 AM
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Next time dont run it to " damn near empty" unless you absolutely have to. Sediment and such can build up at the bottom of a tank and clog your injectors. Warranty on the car?

Quote:
Originally Posted by muchachomaloo
Ok... maybe I am just retarded then :(.

^^ The truth finally comes out.
#6 Old Aug 23rd, 2005, 10:55 AM
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By damn near empty I mean around 1 gallon left.

Only warrantly left is the powertrain warranty.

The car has roughly 77k miles on it, if that tells you anything.
#7 Old Aug 23rd, 2005, 11:03 AM
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ah well that is expected. Fuel pump may be out along with the fuel lines and injectors. Might want to take it in to have it service.

Quote:
Originally Posted by muchachomaloo
Ok... maybe I am just retarded then :(.

^^ The truth finally comes out.
#8 Old Aug 23rd, 2005, 11:42 AM
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Kinda busy this week, anything I can watch for between now and next week that might be a sign of those problems?
#9 Old Aug 23rd, 2005, 04:43 PM
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IIRC your car only needs 87. In many engines, running inproper octane can cause worse mileage and in the case of running too high of an octane, it can cause a rotten egg smell. If your filter is clean, oil is up to date, and tyres are pressured well, then I would do two things. One, run two runs of Techron fuel system cleaner. Two, check your spark plugs. More likely than not, your spark plugs need to be changed. I do not know if your car has a fuel filter or not but if it does, then it may be time to change it.

nothing to say
#10 Old Aug 23rd, 2005, 05:25 PM
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Quote:
Originally Posted by Zac
IIRC your car only needs 87. In many engines, running inproper octane can cause worse mileage and in the case of running too high of an octane, it can cause a rotten egg smell. If your filter is clean, oil is up to date, and tyres are pressured well, then I would do two things. One, run two runs of Techron fuel system cleaner. Two, check your spark plugs. More likely than not, your spark plugs need to be changed. I do not know if your car has a fuel filter or not but if it does, then it may be time to change it.
2x on the 87. I noticed I got better gas milage and acceleration using the lowest grade. Also consider the 02 sensors, they play a pretty big role in how your car does on gas.

Kindfiend

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#11 Old Aug 23rd, 2005, 08:24 PM
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Exclamation

Guys, don't forget sticking brakes.

A sticking caliper (brake always on) will cause just such a sudden drop in mileage ... and may make the car feel sluggish to boot.

After even a short drive, a sticking caliper will be easy to find. One wheel will be noticeably hotter/stinkier/smokier than the rest.

--- Bror Jace
#12 Old Aug 24th, 2005, 06:34 AM
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Normally I notice a 4-5mpg increase when I fill up with premium, which is just about enough to make it worth paying the extra cost.

I'll start filling up with normal gas and see how that handles.

My brakes are probably due for a change anyways, maybe I'll have those checked out too. Thanks for all the suggestions.
#13 Old Nov 12th, 2005, 12:44 PM
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It could be as bad as me i only get 200 Miles on a tank and i use 93 oct...

i dun know what is up with my beast...
#14 Old Nov 13th, 2005, 08:55 PM
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you live in ohio, its almost winter..... It may just be that they have started adding ethanol to the mix in your area already. I'm not sure if that would change your mileage that drastically, but mine dropperd a little when they changed it here in MN.
#15 Old Nov 14th, 2005, 06:29 AM
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Lightbulb

" ... It may just be that they have started adding ethanol to the mix in your area already. I'm not sure if that would change your mileage that drastically, but mine dropperd a little when they changed it here in MN."

I supposed that could do it. A combination of the new, winter-blended fuels being in the stations tanks ... coupled with the colder ambient (air) temps. That 1-2 punch can cause a drop of several percent in fuel economy.

--- Bror Jace
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