The transmission directs the power of your car’s engine to the wheels at a steady speed. This yields the best balance of performance and fuel efficiency even under the most extreme load or temperature conditions. The transmission is made up of more than 2,000 moving parts, all of which need to be lubricated and cooled. Since even “extended life” transmission fluids can lose their effectiveness prematurely, changing your fluid every three years or 36,000 miles may prove more effective and economical in the long run. Old or insufficient transmission fluid can cause the transmission to work harder, transferring engine power less effectively. This can cause a substantial decrease in fuel efficiency. Regularly servicing your transmission fluid can extend the life of your transmission and prevent a transmission rebuild, if not a complete replacement costing $2500 or more. From a safety standpoint, if your transmission shifts unreliably or shifts erratically, you can endanger yourself and other motorists. Although there may not be a high environmental impact, leaking fluids are harmful to children, pets and other animals.