The development of a successful fuel additive requires considerable effort, a large share of which must be expended on the effect of the additive on engine durability. Durability may be affected as soon as the fuel enters the fuel tank and the possibility of such good or bad effects continues until the exhaust gases have cleared the rear bumper. Some of the durability aspects which can be either improved or made more severe are listed, these include fuel system corrosion, carburetor and manifold deposits, combustion chamber and spark plug deposits, engine wear and general cleanliness and bearing, exhaust system and rear bumper corrosion.
It is shown that of seven experimental additives tested in a fleet of passenger cars of one make operated under severe duty conditions, four additives decreased exhaust valve life while three increased exhaust valve life by from twenty-five to fifty per cent. In another make of passenger car operated under the same severe conditions, none of the additives affected valve life. It is also shown that as little as one gallon of additive in 50,000 gallons of fuel may reduce exhaust valve life to half of normal. Increased amounts of the same additive may actually increase exhaust valve life by more than half.
Consideration of all of these factors make it necessary to conduct thousands of hours of dynamometer tests and millions of miles of road tests in a wide variety of engines before a fuel additive can be marketed with assurance that its over-all effects will benefit the ultimate user. The philosophy of durability testing, choice of test equipment and actual test schedules used by Ethyl Corporation in their durability tests are discussed.