The invention provides an automobile engine bay cooling system. The automobile engine bay cooling system comprises a radiator, a water pump, an engine cylinder block, a heater, an air inlet valve and a speed changing box cooler; the water pump, the engine cylinder block and the radiator form an engine cooling circulation, a cooling liquid outlet of the engine cylinder block is divided into three branches, the first branch is connected with the radiator, the second branch is connected with the air inlet valve, the third branch is connected with the heater, the speed changing box cooler is arranged on the third branch to be connected with the heater in series, and the second branch and the third branch are both connected with a cooling liquid inlet of the water pump. Compared with the prior art, a single cooling water branch of the speed changing box cooler is eliminated, the speed changing box cooler is connected with the engine heater in series, and therefore cooling water flow in the engine self water circulation is increased, and passing of normal heat balance is guaranteed; and meanwhile, the amount of cooling water flowing through the speed changing box cooler is increased, cooling lubrication of a speed changing box is guaranteed, and the overall performance of an engine is improved.