Joel Robinson has not been able to convince the folks at the Environmental Protection Agency, Car and Driver magazine or the U.S. Postal Service that his invention significantly reduces gasoline consumption in cars.

But he has been able to convince a U.S. District Court judge. As a result, the Postal Service can't stop him from selling the device, known as the Platinum GaSaver, through the mail. And the government had to pay him nearly $23,000 for expenses he incurred in fighting the agency -- and winning.

Robinson's story illustrates not only the trials and tribulations of inventors, but also a big problem that potential consumers face:

How can you tell whether to plunk down some of your hard-earned money to order an inventor's product through the mail?

Robinson claims that the Platinum GaSaver produced by his National FuelSaver Corp. of Stow, Mass., can increase the gas mileage in an average vehicle between 15 and 30 percent. He says it does this by introducing small quantities of platinum into automobile engines' combustion chambers. According to Robinson, the platinum acts as a catalyst, increasing the amount of gasoline that undergoes combustion from 68 percent of each gallon to 90 percent.

This claim raised eyebrows at the Postal Service, which concluded that National FuelSaver "engaged in a scheme to obtain money through the mail by means of materially false statements," and the agency issued an order preventing the company from marketing its product by mail, according to court documents.

National FuelSaver asked the U.S. District Court for Massachusetts to void the Postal Service's decision.

The Postal Service had alleged that the company had made three misrepresentations: that installation of the GaSaver would increase gas mileage by up to 48 percent or better, that the device had passed an EPA emission-reduction test, and that its fuel-economy claims are supported by research tests.

The company won its case, as Judge D. J. Skinner ruled on Feb. 28, 1984, that the first and third representations were true. And, although the EPA had not approved the GaSaver for marketing -- the second representation -- the judge said that "the misrepresentation, if indeed there was one, was a minor one unlikely to have a significant impact on consumers."

And early this year, the judge also ruled that, because "the government's position in this litigation was not substantially justified," it had to pay National FuelSaver Corp. $22,747.51 for its expenses in the case.

According to Robinson, the GaSaver consists of a rectangular dispenser 7-by-4-by-2 inches containing a solution, which he won't identify, in which platinum and rhenium (to raise the engine octane) are dissolved. The dispenser is strapped under the hood, and the PVC vacuum line is cut in half to permit installation of a new vacuum line from the dispenser. This causes two or three bubbles of air per second to rise through the solution, releasing platinum and rhenium to be drawn through the vacuum lines into the engine.

The GaSaver is sold by mail for anywhere from $39 to $69. Once it has been used for 12,000 miles of driving, the customer has to pay another $39 for two new vials of platinum, which will last for another 12,000 miles, Robinson said.

The EPA has not fully evaluated the Platinum GaSaver because the company has not submitted data from tests conducted by one of the agency's approved private laboratories, according to Merrill Corth, EPA's device evaluation coordinator. Corth said EPA therefore compared GaSaver with similar devices and concluded that it saw no reason to believe that it would aid fuel economy because not enough platinum was being introduced into the engine. Robinson said tests were run at an approved lab but, because road vibrations help the GaSaver to work and the tests were conducted without actually driving, the data did not reflect the GaSaver's performance.

Corth said that EPA has been testing alleged fuel-saving devices for cars for 15 years and that only one or two reduce fuel consumption -- and those by very small amounts. "A lot of people -- especially the inventors -- do believe these devices work. And they don't," Corth noted.

Don Sherman, Car and Driver magazine's technical director, said that none of the 15 or so fuel-saving devices that his magazine has tested over the past 15 years have worked. He said that injecting platinum into an automobile engine is "an absurd proposition" because it could not act as a catalyst in the engine because of the lack of a large enough surface area.

Robinson responded by saying that this would be true if the platinum were bonded to the engine's interior, as it is to the inside of a catalytic converter. But because the platinum is floating free in the engine, it presents enough surface area for the catalytic reaction, he asserted.

Robinson said that he started National FuelSaver in 1977 to produce and sell a product that was similar to GaSaver but was designed to reduce fuel consumption in -- and pollution from -- industrial oil and coal furnaces. Then he adapted the idea for the GaSaver. He said that, since he began shipping the device in April 1979, he has sold 40,000 units. He also said that he owns the company and holds two patents for the invention.