Distribution transformers are designed to operate in an oil temperature range named the allowable range. This range depends on various factors such as the insulation class of the coils, the cooling fluid, the cooling method and the environmental conditions. If a transformer operates at a low temperature, its insulation life will increase. Based on this fact, it can be said that temperature is an important factor in transformer optimization. One of the major problems of the power distribution network is the overheating of the distribution transformers during the summer that resulted to failure and damage of that. Increasing the load due to the use of cooling devices and solar radiation on the transformers causes them to heat up and helps to increase its temperature. The normal life of transformer insulation is 85, 000 hours, which is equivalent to 10 years for Class A insulation. This life is halved or doubled for every 8 degrees of rise or fall of the specified value. Hot spot temperature is one of the important and key parameters in determining the insulation life of the transformer. The hot spot temperature of the transformer depends on the ambient temperature, high oil temperature and coil temperature. Also, the temperature of the hot point of the coil is a function of wind speed, thermal radiation of the sun and the height of the transformer installation relative to the sea level. In the present article, the effect of oil type, solar radiation, color and external environmental factors on the heating of distribution motors is reviewed and investigated experimentally and analytically.