It is most likely that it is because of the thermostat, they may previously take it away, or simply stay open, but it is unlikely, because when they fail they produce temperature problems, but at the reverse, they get hot, while at more speed transitas the radiator will ventila The thermostat works, to prevent the engine from working at a low temperature, the ideal is that it always works in the normal temperature, the two accessories that the engine has for it are the thermostat and the fans, these can be Motores elétricos, ou outros com controles viscosos, outros que são ativados por uma temperatura do sinal elétrico prejudica o motor. Espero dissipar um Tantito a dúvida sobre a temperatura do motor.