Does Ethanol Affect Fuel Economy, Replacing An Oxygen Sensor, How Plug-in Vehicles Work, Preventing Moisture Inside Windshield: Mike Allen's Weekly Online Auto Clinic

Q: I pay attention to the factors that result in good gas mileage for my car, like checking tire pressure, spark plug gap, clean air filter, fuel pump pressure, clean transmission fluid, etc. Since I started using gasoline with "not exceeding" 10% ethanol, my fuel economy has decreased by almost exactly 10%, average and highway driving. Does the gas/ethanol mix have inherently less potential energy that straight gas? If so, because most ethanol is corn based, are we being hit with a double whammy of higher food prices and less efficient gasoline?

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A: Ethanol has approximately 2/3 the energy content of gasoline. Vehicles running on E85, a mixture of 85% ethanol and 15% gasoline, routinely see a 20-30% decrease in fuel economy/gallon.

The 10% ethanol blended gasolines across the country should have about 96-97% of the energy in straight pump gas. In theory, there should be little enough to change in economy to notice. On the other hand, a lot of PM readers mirror what you say: i.e., a 10% (or more) decrease in fuel economy.

Frankly, I have to be suspicious of any real-world anecdotal testing. It's way too easy to inadvertently influence fuel economy with subtle changes in driving style. Add in the fact that it's impossible for most people to tell what the actual ethanol content of gasoline is—the pump says it may be as much as 10%, but who knows?

10% Ethanol is added to gasoline for emissions reasons, to reduce CO output during the summer. It's not a conspiracy between the petroleum companies and the Corn Belt Mafia to reduce your fuel economy.

Q: A couple of years ago, I read an article about a tinkerer in India who modified the pistons in his car by adding a dimple in the face of the piston head. The result was a remarkable increase in power and fuel efficiency. I would very much like to find this article again. Can you help?

A: I can't help you because that article was in Popular Science, not PM. This revolutionary technology seems to have gone nowhere, however. Which makes me doubt the veracity of the story.

Q: I have a 1996 Ford Contour and i want to remove the upper O2 sensor to clean it but i can barely turn the wrench because of the fan assembly and its a bad spot to get leverage. There is also a bolt holding the parts together right next to the sensor and the wrench doesn't work that way. Is there a way to remove it without having to remove the fan and other parts?

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A: Welcome to the nightmare that mechanics have to deal with every day. Now you know why mechanics have so many different kinds of wrenches and sockets. If one won't work, you can usually find one that does.

See if a specialized oxygen sensor socket helps.

And you might look at this Saturday Mechanic story on oxygen sensors we did while ago.

Oh, by the way: never clean an oxygen sensor. They're not like the spark plugs in your lawnmower. If you've got one out of spec or not working, just replace it.

Q: Other than the power plants not getting any money for the power used for plug-in hybrids, why can't the manufacturers put an alternator or generator on these cars to recharge the battery as they do on gas power cars?

A: The power companies most certainly will get money for the electricity used to charge electric vehicles and PHEVS. That electricity goes through the meter just like all the rest of the electricity the runs your lights, TV, and air conditioning. I can't imagine why you would think it was free.

Plug-in hybrids do have a generator and motor on board. That's the definition of a plug-in hybrid. It uses electricity from the grid to charge a battery pack, which propels the car for the first 20-40 miles. After that, you can either plug in and recharge from the grid again, or continue driving and the engine and generator will provide power. Of course, now you're burning gasoline or diesel, but at least you can get home.

Q: The inside of my windshield keeping getting a frost buildup overnight. Any clues as to why and what i can do to prevent it?

A: You have moisture inside your car. If you reduce the amount of moisture in the car overnight, there will be less on the windows in the morning. Obviously.

Where's that moisture coming from?

Start by making sure you are not bringing it in with you. Knock the snow off your shoes before swinging your feet inside. Eventually, if your car gets a lot of wintertime use, the carpets can become saturated with snow melt. If you have mats or removable carpets, bring them inside somewhere warm overnight to dry off. If the glued-down carpets are wet, park the car inside with the windows open to dry the carpet out. If you don't have access to a heated garage, an electric space heater in the footwell could do the job.

Check that the drain hose out of the evaporator core is working. That's where the water comes from that you see dripping out of the bottom of cars on humid days when the a/c is on. And, no surprise, your a/c is sometimes on during the winter. It's used in the DEFROST setting to—you guessed it—remove water from the air being blown onto the windshield. There's a tube that lets this water drip out of the car—and if if it's plugged with lint, leaves or just frozen, water can back up into the car interior.

Check for leaky door or sunroof gaskets allowing water inside, probably manifested as wet carpets.

Once you you've got the inside of the car dried out, keep it that way. Just before you park the car for the evening, set the air conditioning system to the RECIRCULATE or MAX COOL setting. This will close the vents under the dash that let in outside air. Cool, humid outside air, which will fog up the inside of the windows overnight.

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