Abstract: For decades the slow accretion of carbonaceous deposits on the upper cylinder areas of the internal combustion engines has acted to impair optimum performance and to significantly reduce gasoline or Diesel mileage per gallon. It has now been discovered that these formerly rather intractable engine deposits can be efficiently removed by dispersing and dissolving them through the use of optimized mixtures of polar protic and dipolar aprotic solvents that have the essential capability of acting in concert synergistically. For practical reasons these solvents must have a melting point higher than about 41° F. (5° C.). The finished product must also have a dielectric constant of about 20 and a pH value of at least 11.0 at 77° F. (25° C.). These parameters are considered vital to success. For example, in a test using a blend with a dielectric constant of 15, the removal of the carbonaceous deposits was either de minimus or very limited, even at pH values of 12.0 at 77° F. (25° C.) or higher.