Can be attached to the back of the radiator and increases the efficiency of the engine fan by forcing air to be pulled through the radiator instead of around it. More importantly, it keeps air that does go through the fan from spilling over the tips of the fan blade, and from recirculating around the ends of the blades to pass again through the fan. The combination of an improved fan and use of the radiator cowl gives a marked improvement in cooling at low speed. Please check also if the fan is correctly installed. This problem is actually quite common, as some people mistakenly install the blade backward figuring it should be farther away from the radiator.