In the present work a three-dimensional analysis is used to study cooling performances of copper- ethylene glycol nanofluid through the flat tubes of an automobile radiator to evaluate their superiority over the base fluid. A numerical simulation is carried out by solving the governing continuity, momentum and energy equations for laminar flow. The investigation covers Reynolds number, inlet temperature and nanoparticle concentration level in the ranges of 10-125, 348-368K and 0-2% respectively. The effects of using the nanofluid on the heat transfer inside the flat tube are investigated. Numerical results have been validated by comparison of simulations with those available in literature.