Whenever fuel prices rise, our inboxes get topped off with press releases breathlessly claiming gains in miles per gallon simply by strapping something to a car’s fuel line, injecting air or water into the engine, splitting hydrogen out of water to use as fuel, or pouring a bottle of additive into your fuel tank.

Instant fuel economy improvers are good for more effectively vaporizing the money in your wallet, and little else. But there must be a market for this stuff, or else these companies wouldn’t exist to send us their annoying sales pitches.

If someone you love is at risk for wasting money on a product advertised to make a Suburban sip fuel like a Volt, direct him or her to this page on the Federal Trade Commission web site, this excellent test that Popular Mechanics did a few years back or this short piece by Consumer Reports.

If they insist that better gas mileage is just a credit card number and expiration date away, tell them to consider one of those meters that plug into the OBDII port on 1996 and newer cars and offer instant feedback about MPG as well as keeping track of the car’s average.

Many newer cars have this built in, but older vehicles don’t. There are a few of these accessory gauges on the market, and if you poke around over at Ecomodder you’ll find various discussions about these devices.

Of course, on cars without OBDII, you can always hook up one of the old vacuum gauge type economy meters that have been around forever and started showing up on production cars in the fuel crunched 1970s.

The key to these gauges, either electronic or vacuum, of course, is that they help the driver modify his or her own behavior rather than modify the vehicle in some way – which is actually the most sure-fire way to achieve better fuel economy.