Is it safe to use synthetic oils in transmissions and rear ends?
If the oil has the proper additives for the materials, it is safe to use synthetic gear, transmission and power steering fluid in a street rod or restoration car. What is an API rating? How is different from an oil’s viscosity rating? The viscosity ratings of the oil describe the cold start and high temperature flow rates of the oil. A 0W-30 flows better at start up than a 10W-30. The number before the “W” is the cold start viscosity, so the lower the number, the easier it is to start the engine. The higher the number, the more power it takes to turn the motor over when you hit the ignition. The number after the “W” is the high temperature flow rate of the oil. For example, while a 0W-30 flows better at start up than a 10W-30, both oils flow like a SAE 30 grade at high temperature (212F). The higher the number after the “W”, the heavier the oil is at higher temperature. A 5W-40 is a heavier oil at high temperature than a 5W30, so SAE viscosity ratings only tell you about the flow chara
