Combustion engine (E) provided with a Waste Heat Recovery System (WHR) draining thermal energy from an exhaust pipe (EP) of the combustion engine (E) in order to produce mechanical energy (ME) by exploiting ethanol or ethanol based medium as working medium, wherein the combustion engine comprises injection means (EJ) to supply the combustion engine with a fuel, and wherein the WHR comprises: - a WHR circuit comprising the following components, arranged in succession according to the circulation of the ethanol or ethanol based medium in the WHR circuit: a) a pump (P), b) a main heater (HE), c) an expander (EX), d) a condenser (CD), - a fresh ethanol tank (ETH-T) able to contain fresh ethanol or ethanol based medium and connected with a first point of the WHR circuit via a first control valve (V1), to replace ethanol or ethanol based medium circulating in the WHR circuit with the fresh ethanol or ethanol based medium, and - a pipe connection (D-ETH) and a second control valve (V2), connecting a second point of the WHR circuit with said injection means (EJ) in order to supply the combustion engine with ethanol or ethanol based medium from the WHR circuit, and wherein the combustion engine further comprises control means (CPU) adapted to perform the following steps: - adjusting a highest temperature of the ethanol or ethanol based medium in the WHR circuit, even beyond a predefined critical temperature of the ethanol or ethanol based medium, - estimating a thermal degradation of the ethanol or ethanol based medium in the WHR circuit according to the highest temperature reached within the WHR circuit, - adjusting the replacement of a degraded ethanol or ethanol based medium circulating in the WHR circuit with said fresh ethanol or ethanol based medium, by opening said first and second control valve (V1, V2). - a WHR circuit comprising the following components, arranged in succession according to the circulation of the ethanol or ethanol based medium in the WHR circuit: a) a pump (P), b) a main heater (HE), c) an expander (EX), d) a condenser (CD), a) a pump (P), b) a main heater (HE), c) an expander (EX), d) a condenser (CD), - a fresh ethanol tank (ETH-T) able to contain fresh ethanol or ethanol based medium and connected with a first point of the WHR circuit via a first control valve (V1), to replace ethanol or ethanol based medium circulating in the WHR circuit with the fresh ethanol or ethanol based medium, and - a pipe connection (D-ETH) and a second control valve (V2), connecting a second point of the WHR circuit with said injection means (EJ) in order to supply the combustion engine with ethanol or ethanol based medium from the WHR circuit, - adjusting a highest temperature of the ethanol or ethanol based medium in the WHR circuit, even beyond a predefined critical temperature of the ethanol or ethanol based medium, - estimating a thermal degradation of the ethanol or ethanol based medium in the WHR circuit according to the highest temperature reached within the WHR circuit, - adjusting the replacement of a degraded ethanol or ethanol based medium circulating in the WHR circuit with said fresh ethanol or ethanol based medium, by opening said first and second control valve (V1, V2). <EOS>