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car fuel mileage

L

luapp

Member
my sis has 2009 mercury mariner v6 she was complainen about her mileage. it has the digitale readout it always got like 20 to 22 mpg and all of the sudden before it got cold it went to 12 or 13 mpg and stayed there any ideas thanks
 
(quoted from post at 01:49:58 01/25/13) my sis has 2009 mercury mariner v6 she was complainen about her mileage. it has the digitale readout it always got like 20 to 22 mpg and all of the sudden before it got cold it went to 12 or 13 mpg and stayed there any ideas thanks
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Get an OBD2 scanner and see what codes it throws. Could be a mass air flow sensor or O2 sensor problem.
 
I wouildn't trust the digital readout, what is she really getting for milage. Miles driven divided by gallons pumped in? That is the most accurate way of getting mpg. My wifes car is off 15%, that alot in my book. Is she letting it warm up for half an hour everyday? My truck has been known to get 2-3 miles per gallon in the winter, then again I rarely drive it-2002 K2500 with 8.1 gas hog, pocket drainer and optional 4.10 rearend. I get 8 mpg on a good day.

Nate
 
A mass air flow sensor can get dirty and cause poor mileage. There is actually a cleaner specifically for mass air flow sensors, I tried it today on my 03 2500HD, I suspect i'll know in a couple of weeks if it made a difference. Jim
 
(quoted from post at 22:46:49 01/24/13) I wouildn't trust the digital readout, what is she really getting for milage. Miles driven divided by gallons pumped in? That is the most accurate way of getting mpg.
Click to expand...

The newer Fords dash computer actual measures based on the fuel put through the injectors(pressure*Pulse time*revs/ABS wheel revs). In every case where I have ever checked they have been within 5% of what the "fill it up and watch your miles" method gives, IMHO 5% is as close as you can get with the fill up method. As such I'd trust the dash first. Pretty fun toy to play with when you reset it at a stop light and screw around some.

Short trips and cold weather will make your mileage suffer terribly. Particularly if you let the car "warm up". My daily driver DOHC V6 Ford is is under 20 right now an usually does 27 or so.

Pushing snow, snow/studded tires?, increased rolling resistance from lower tire pressure, more alcohol in the fuel, warm ups... it all adds up.
 
Start with Dignostic Trouble Codes (DTC's) to see if there are any obvious problems. The engine compartment should be checked to see if there are any hoses that have cracks in them or have fallen off of their connections including all of the tubes that connect to the intake air plenum. The next classic problem areas are thermmostat stuck partially open so it never heats up and also a partially plugged exhaust. Moving on from there I would begin to suspect oxygen sensors and misfiring due to spark plug or coil issues. After that MAF, TPS, MAP and other sensors would be suspect. Has the vehicle had an air cleaner changed and oil and filter changed recently? Are all the intake air systems intact and factory original?
 
We"ve got a 2008 Mercury Mariner,Premier Edition,
with a 3.0 liter V-6. The dash fuel meter says,
24.9 to 25.3 on long trips, but dividing mileage
by gallons shows 26.4. Over 65 miles per hour the
mileage drops,(about 20 mpg at 70 mph)so I stay in
the right lane and set the cruse control at 60,
and let the speeders pass this "old Guy".
 
We have an '07 Ford 500 and the computer gives the same result as manual calculation. It's surprisingly accurate.

I usually get between 31 and 32 with mostly highway miles but on some tanks it will drop to 29 or even 28. I think there's a difference in the fuel density from station to station or batch to batch that is hard to account for.
 
Vern mentions a stuck thermostat. I never realized what a difference that makes until the thermostat went bad in the wife"s Explorer. Mileage dropped off 3-4 MPG in the dead of winter. New thermostat and it went right back to normal.
Heater worked a lot better too!! LOL
 
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