I think you'll go though a lot of dry cell batteries with a radiator fan. That's why I suggested a computer fan. Around here we have a Fry's electronics. They have 12v computer fans for about $12, in many colors, designed to move air using very low power. With all the colors, including black and clear, you can even make a popular fashion trend statement.
http://www.frys.com/search?cat=-69582&pType=pDisplay&rows=25&resultpage=2&start=50&rows=25The human eye can't see heat. Short of touching the motor, the only option for heat determination is instrumentation. You can buy an infrared Thermometer at Harbor Freight for about $20, that you can take out of your pocket and check the engine temps while waiting in traffic.
Signs of overheating are poor shifting smoothness/dragging clutch due to the oil changing behavior from heat damage. The next sign is the engine slowing down due to pistons seizing in the bore. Both these signs are after some damage has occurred either to oil or engine and should be avoided.
Overheated oil is damaged oil and should be replaced ASAP. Synthetic oil can withstand higher heat and still provide needed lubrication to save all the metal bits. But, it has a withstand limit as well. A blend of oil type is less costly yet still has some synthetic to help the motor survive.
Oil coolers will help the oil survive over temp conditions. It does very little to keep the engine itself cool. It's is not an oil cooled engine design. That's why the huge fins and large surface area on the outside of the motor are exposed to the surrounding air to accept waste heat. However, saturated heat laden air can only accept heat from a hotter source than what it has currently attained. 300 degree air won't take heat from a 275 or 300 degree surface. That's why you have to move the hot air away and replace it with the abundant ambient cooler temp air in the vicinity.
