Wednesday, May 23, 2007

98 Jeep TJ - Gas Mileage Experiments - Testing Acetone.

If you own one of these things, then you know why I'm talking about this. Mine is a '98 2.5 liter. It has all the power, loud noise, and my personal favorite, bad gas mileage. You'd think a four-cylinder would be fuel efficient. You'd also be wrong.

To be fair, this engine has over 80,000 miles on it and has been completely bulletproof. If the gas mileage were better, I could live with the lack of power...I could rationalize it as a tradeoff.

I can't do much about the power, or lack of it, but I have had some minor success in the gas mileage department. The thing about Jeeps is that they remind you of the importance of good aerodynamic design. Every mile in a Jeep is a rolling battle with the molecules of air that don't wanna get out of the way. And instead of coaxing them gently to the side, the Jeep rams its way through like a rabid bull.

That makes it hard for the TJ to maintain speed going up steep hills on the freeways. It also makes the gas mileage take a nosedive.

So, for over a month now, I've been avoiding the freeway on the trip to work. Fortunately for me, I was able to find a route that takes just about the same amount of time as the freeway trip.

I used to get roughly 230 miles out of 13-14 gallons of gas. That's roughly 16-17 miles per gallon. When I cut out freeways, my gas mileage improved to between 18.3 and 18.9 MPG, and my distance per tankful increased to 250 miles or more. Not much, but it's a start.

Something else I plan on trying...I'm going to inflate my tires to 38 psi to reduce rolling resistance. Also, take Jeep's advice and follow the horrible, annoying shift light. Hopefully those will make a difference, too.

Another thing that I am trying is somewhat controversial. It is said that adding 2-3 oz of acetone to every 10 gallons of fuel will result in a gas mileage increase. I've read all over the internet about people doing this and achieving significant mileage gains. I've also read about Mythbusters trying this unsuccessfully. I've ALSO read that Mythbusters did not conduct the experiment correctly, and that yes, by Golly, it really does work! So, since there's so much contradictory information about it, I decided to try it myself.

The story is, you're supposed to use 100% pure acetone, and that decreases the surface tension of the gasoline, allowing it to vaporize more completely, yielding more power per piston stroke. At my local drugstore, "pure" was labeled as "professional" quality fingernail polish remover, consisting of "100% Acetone". It was about $4 for a 16 oz. bottle. According to my tank size, that should be enough to treat 3 tankfuls of gas. That's about $1.30 extra per tank, at least for me. It will be interesting to see, should there be any benefit, if it will be great enough to offset the extra cost.

Yesterday, I filled the tank and put in the acetone. Today, I drove it for the first significant amount of time, on the way to work. I didn't notice much, except for one took longer for the engine to come up to full operating temperature. About 3-5 minutes longer. And, at first, when the thermostat would cycle on and off, the temperature would drop significantly, according to the temp gauge. Usually, with most late 90's Jeeps, the temp doesn't stray far from 210 degrees, but it was coming down considerably during thermostat cycles. By the end of my commute, the temp gauge was firmly at 210, like always, but it took longer to get there, because the engine wasn't generating as much heat. And everyone knows...a well cooled engine is an efficient engine, right?

Time will tell if this makes any difference. My gut says no, but I figured, for $4, what's the harm in trying?

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