A system for an internal combustion engine (10) arranged for being powered with a fuel mixed with a lubricant, which system includes:—a detector (16) arranged for detecting the presence of a given additive in the lubricant mixed fuel—an electronic module (24) arranged for comparing the detected presence of the additive with a predetermined threshold value, and designed so that if the lubricant is not mixed in the fuel, or has been mixed in the fuel in an amount lower than a through the additive against the threshold value correlated amount, by means of an indicator (30) indicate that a lack of lubricant is at hand in the fuel and/or by means of a connection (26) to an ignition or injection system (11) for the engine (10) prevent or modify the operation of the internal combustion engine if said lack of lubricant is at hand in the fuel. The invention also refers to the method of how the system operates.