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  #1  
Old 02-21-2013, 09:23 PM
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O2 Sensors and MPGs

Well I've had my Jeep for about 13 months now and put about 25,000 miles on it. It's been a pleasure not to pay over $75/ week filling up like my last gas hog.

In my first 6 months or so I would routinely get well over 25 on long highway trips. On local two-lanes with few stops and minor elevation changes I'd get up to 27.

However over this past winter I've noticed my MPGs are not what they used to be. Now I seem to be getting less than on long trips, not even hitting 23. I'm wondering if it's simply due to winter conditions or are my O2 sensors not up to snuff. Most of my trips have been on dry roads, so I'm not factoring in snow-trips when I dial it into snow mode.

No codes present, and the engine runs just as smoothly as it always have.
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Old 02-22-2013, 12:59 PM
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Re: O2 Sensors and MPGs

I typically see a 20% or so reduction in mileage in the winter.

1. Winter gas. More additives etc. equals less BTU's equals lower mileage.
2. Winter tires. Softer compound equals more rolling resistance equals lower mileage.
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Old 02-22-2013, 07:40 PM
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Re: O2 Sensors and MPGs

X2 on winter gas even worse with winter diesel
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Old 02-22-2013, 09:32 PM
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Re: O2 Sensors and MPGs

Snow/slush on the road also adds drag as do extended warmups.

Just guessing though, we do not have that here.
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Old 02-22-2013, 11:19 PM
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Re: O2 Sensors and MPGs

I also have the problem which I think most do right now because of all of the above reasons.
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Old 02-23-2013, 08:21 AM
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Re: O2 Sensors and MPGs

I'll 2nd or 3rd the gas formulation. Ethanol content can be to blame as well. Even though it has not been terribly cold in the Mid-Atlantic, cars use more in the winter. Colder air is more dense. Thus, additional fuel is added to the mix to keep the A/F ratio correct.
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Old 02-23-2013, 11:11 AM
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Dense air doesn't make sense to me. I'd just be using less throttle for s given power output.
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Old 02-24-2013, 06:23 AM
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Re: O2 Sensors and MPGs

I think the biggest contributor is the increased use of ethanol in the winter blends which generates less energy than "pure" gasoline.
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Old 02-24-2013, 11:28 AM
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Re: O2 Sensors and MPGs

Quote:
Originally Posted by Yadkin View Post
Dense air doesn't make sense to me. I'd just be using less throttle for s given power output.
Air density is the mass of air in a given volume. It is dependent on temperature and pressure. Lower density means less oxygen available for combustion, higher density beans more oxygen is available (per given volume). Much like adding a supercharger; more fuel is added to maintain the optimum A/F ratio. The reverse happens at higher altitudes.
Your throttle input isn't controlling the ratio. The ECU makes that decision based on temp, intake pressure, load, etc. and adjusts injector duration accordingly.
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Old 02-24-2013, 12:50 PM
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Yes I understand thermodynamics. That's why colder air results in a smaller throttle opening for a given power output. You burn the same mass of O2. Now if the partial pressure varied with temperature you'd have a point.
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Old 03-02-2013, 01:19 PM
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Re: O2 Sensors and MPGs

Spend time & fuel warming it up before driving?
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