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Discussion Starter #1
I was consistently getting 33 - 34 MPG with my normal driving. I hit 3500 Miles and decided to change oil. Went with Pennzoil Ultra and K&N Oil filter. Same driving habits and I am down to 31 MPG. Only other thing that has changed it I pumped tire pressure up a little..38 all around. Anyone else switch oil and have this issue? I have never seen this before.
 

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Winter gas has arrived. Winter formula gasoline has lower mpgs...
With a really high efficiency car like the Focus, the difference is more than 2mpg..
So figure you gained at least one for the oil, and lost three for the poorer quality winter formulation gas.
For all sorts of articles about "winter gas formulation" in Google.

It has something to do with the lower volatility gasoline (desired in Summer) portion costing more for, but that also gives a little better mileage.
So going back to Winter, the gains from that stuff is gone.

Raising the tire pressure should help a little.
I have my front at 44psi (the firmness in the front is less noticable due to the engine, and it give better handling) and 37psi in the rear. (any higher psi in the rear just creates a really harsh ride)

So your oil did not cause the loss in mpgs.. IMO anyway.
 

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I was consistently getting 33 - 34 MPG with my normal driving. I hit 3500 Miles and decided to change oil. Went with Pennzoil Ultra and K&N Oil filter. Same driving habits and I am down to 31 MPG. Only other thing that has changed it I pumped tire pressure up a little..38 all around. Anyone else switch oil and have this issue? I have never seen this before.
Is the new oil 5W20 ?
Different oil and filter combinations can cause a slight increase or decrease in oil pressure which could affect fuel consumption slightly.
Ford themselves brag about their oil being specially designed for increased MPG.
Mobil 1 also makes this claim.
Thicker oil causes oil pressure to increase.
How is the level? Not slightly overfilled ?
 

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Your problem, I think is your use of a K&N air filter. The MAF or mass airflow is very sensitive. They have a special cleaner you can use to clean the MAF you can get from a NAPA auto parts store. The oil mist from your K&N air filter does affect your MPG. I just found that if the large hose from the air filter to the intake manifold is laying loose & only partially covered the intake manifold opening that my Focus ZX3 (16 valve engine) wouldn't start. I assumed all kinds of other problems but when I discovered my mistake & connected it properly, my Focus started & ran like a champ. I am a great fan of Amsoil & have used it after putting on the first 2000 miles. My 2001 ZX3 5 speed now has almost 144,000 miles & I just changed the oil & filter after over 25,000 miles & over 2 years since the last change. Last year after one year I had to add one quart & when I changed the oil last week it was still at the full mark & my oil analyser said the oil was still good for further use. I have been running Amsoil's top of the line 0W30 "signature" synthetic.
 

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FWIW, if a K&N air filter is oiled properly there will not be any oil mist.

I have been using them since the early 80's and have either had no change or a very small positive change in economy/power.

BTW, the OP is using a K&N oil filter not air filter.
 

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Discussion Starter #7
Yes K&N Oil filter not Air filter. Although, I am considering that as well. I am going to try 89 Octane next fill up. Maybe Winter gas is the cause. Very odd though. Probably did start after Synthetic oil, but, that also was the time of winter gas and colder temps.
 

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Is the new oil 5W20 ?
Different oil and filter combinations can cause a slight increase or decrease in oil pressure which could affect fuel consumption slightly.
Ford themselves brag about their oil being specially designed for increased MPG.
Mobil 1 also makes this claim.
Thicker oil causes oil pressure to increase.
How is the level? Not slightly overfilled ?
+1 on this point. Are you sure you put the correct oil in? Synthetic is said to deliver better mpgs but the viscosity needs to be correct... how many tanks/ miles have you observed the decrease?
 

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The K&N oil filter might be harder to push the synthetic oil through? I'll probably just stick with the Motorcraft with my 0W-20 Mobil1 synthetic.
 

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Yes K&N Oil filter not Air filter. Although, I am considering that as well. I am going to try 89 Octane next fill up. Maybe Winter gas is the cause. Very odd though. Probably did start after Synthetic oil, but, that also was the time of winter gas and colder temps.
I fill up with 89 or 90 have a K&N filter and use castrol synthetic getting about 32mpgs with a stick.
 

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My current mileage is hanging around 35mpg to 36mpg.. with combo city/local freeway driving.
It is down from earlier, but i am hoping it stays at least up around where it is now.. as temps drop.
 

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My current mileage is hanging around 35mpg to 36mpg.. with combo city/local freeway driving.
It is down form earlier, but i am hoping it stays at least up around where it is now.. as temps drop.
That's excellent Elizabeth.

You've got your Focus running "on the sniff of an oilrag".
Well Done.
 
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