MPG improves on PU with tonneau cover?

The beginning of this month I bought a soft tonneau cover for my 97 Nissan PU, 2.4 l, 4 cyl FI, 62,500 miles. He's a good old boy and looks
almost as good as when he was new. I buy him a present every once in a while. Last time it was a cat-back dual exhaust, and the time before that, a keyless entry system. When I installed the cover, I had about 3/4ths of a tank of gas left. Since driving it with the cover on, it seemed that my trip odometer was getting a higher reading compared to my gas gauge than before. I usually traveled 50 miles between the 1/4 markings on the gas gauge, winding up with about 190 miles with about an 1/8th tank of gas left when I refill it. I got to 212 miles with about an 1/8th tank left. When I filled the tank yesterday and made the MPG calculations from my last fill up, it seems that I was getting 18.34 MPG. I rarely put more than 11-12 gallons in the 15-7/8 gallon tank. This time, it was 11.595 gallons. Before the cover was installed, I was averaging around 16.5 MPG. The last time I filled up before the cover, I got 16.62 MPG. I haven't changed my driving habits despite the rising gas prices, or made any long trips, so it may be aerodynamics. The next time I fill up, the MPG will be calculated with having the cover on for the entire period between fill ups, so we'll see what develops. Watch the mpg drop and burst my balloon! :-)
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Bill
In Hamptonburgh, NY
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I've read that a bed cover does give better mileage. The tailgate acts as a spoiler with a lot of drag,so blocking the airflow into the truck bed reduces drag.
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Jim Yanik
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willshak wrote:

Some mpg savings is to be expected. You have eliminated the rolling low pressure drag zone in the bed and created a boundary layer. The worst thing you can do is drive with the tailgate down, or off, or with one of those air gate things. However, to accurately determine the mpg, you will have to fill up the tank. "About" 1/8 tank is not good enough. Your gas gauge is not linear, either.
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wrote:

There are some detailed studies you can read on this... the cover would generally help, but you can get people to argue both sides. Depending on driving speeds, styles\, and conditions, you could find better results in a lot of different ways (same as other changes to a vehicle).
Bottom line is that what counts is whether _your_ mileage improves.
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on 4/25/2008 8:13 PM Paul said the following:

I 'fill up' when the gauge gets 'down' to about 1/8th of a tank, not just put 1/8ths of gas in the tank.
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Bill
In Hamptonburgh, NY
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who cares ! did you buy the cover for gas savings ? Dick

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on 4/26/2008 7:27 PM D. said the following:

Well, you care enough to comment. Dick is a good name for you.

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Bill
In Hamptonburgh, NY
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why don't you stick the cover in your ass , ASSHOLE !!!!!!!

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D. wrote:

I bought mine to cover the illegal aliens I employ........
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Urban Legend
This theory was disproved on Mythbusters an while back
I'm glad your getting better mileage but I don't thing the cover is causing it

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