Drive It Forever

High gas prices spur interest in maximizing mileage. Prices were well above $4 in San Jose, Calif., last week. (Marcio Jose Sanchez/Associated Press)

Q. My dad is thinking about installing an electrolytic hydrogen generator under the hood of his car. The idea is that water will be broken down into hydrogen and oxygen, which will then be fed directly into the intake manifold, thereby increasing gas mileage.

It kind of makes sense, but I'm still skeptical. The only way I can see you getting better mileage from such a setup would be by changing the air/fuel ratio, which would also require you to change the timing. That's assuming you have a reliable, regulated source of hydrogen.

I've spent all afternoon scouring the Internet, but have found very little credible information, and nothing at all on the Popular Mechanics website. Most of what I found looks like snake-oil salesmen offering you, for a small fee, instructions on how to build your own system.

What is your take on this fad? If it were an actual alternative fuel, wouldn't the aftermarket be teeming with manufacturers putting out higher-quality kits for this mod?

A. It's bunk. It will take more energy to separate the hydrogen and oxygen from the water than can be regained by burning it in the engine.

Q. Have you ever heard of "HHO gas" and its ability to significantly boost your miles per gallon?

The system is based on producing HHO gas from water by using electrolysis. The water is supplied by a container under your hood; the electricity is provided by the vehicle's battery. I have seen many postings of improved fuel efficiency ranging from 15 to 50 percent.

If this is true, why doesn't the automotive industry provide this already? The system could be homemade, and materials should be less than $100. It would pay for itself in a month or two.

A. I'll label it a hoax right here.

This whole principle ignores the second law of thermodynamics. In short: There can never be enough energy gained from burning the HHO to provide enough electricity to disassociate the water. Otherwise, it would be perpetual motion. Mileage increases? Voodoo.

Q. How much synthetic oil has to be added to mineral oil in order to call it "blended oil?" Is it one drop, or is there an unwritten standard minimum amount?

A. This is from Mobil's website: "Semi-Synthetics use base stocks comprising conventional or hydro-processed base oil in combination with severely hydro-processed or synthetic (PAO) base stocks. The proportion of severely hydro-processed or synthetic base stocks in semi-synthetic oil is a closely guarded secret, but it is usually between 10 and 25 percent."

Which doesn't sound like very much for the price they're getting.

Q. I'm trying to grease a set of universal joints, but the small grease zerks, the lubrication fittings through which the grease is applied, are set so deep in the universal that I can't attach my grease gun. I'm short about one-eighth of an inch. Can you help?

A. I've got half a dozen different grease-fitting connectors for my grease gun, from angled to flexible and right-angle. And on some vehicles I seem to need almost all of them to get to all of the zerks. Try a different fitting. Once in a while I've had to remove a zerk and replace it with one I could actually grease.

Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com.