A method for adjusting a fuel composition to increase liquid fuel heat tolerance is described that includes directly injecting a first fuel (such as liquid propane) to the engine via a fuel rail when a fuel temperature falls below a threshold; and in response to a fuel temperature greater than a threshold, directly injecting a liquid mixture of the first fuel and a second fuel (such as gasoline) via the fuel rail. For example, gasoline may be added in sufficient amounts to the liquid propane to ensure the mixture remains a liquid during engine operations. In this way, the amount of gasoline introduced into the propane may be based on an extent of the fuel temperature above the threshold which further acts to extend the operating range of the first fuel.