Transmission fluid is where the lines start to get a little foggy. Manual transmissions typically use heavy-duty gear oil to lubricate them and require far less attention than their automatic counterparts. There are also CVT-type transmissions now being used, and they are completely different.
Women ‘n’ Wrenches will worry about the more complex maintenance operations in a subsequent feature, but for now, if you don’t have a dipstick somewhere on the top-side of your engine, you needn’t worry so much about checking it. (That’s not to say you don’t have to worry about it, but sealed transmissions are better off left to a service facility, for now.)
If you do have a “checkable” transmission fluid level, the procedure for checking the automatic transmission fluid can be very unusual, but by design, must be performed a certain way – usually with the engine running.
It is also one fluid that must be checked warm, in many cases, after the transmission has had a chance to cycle through the gears and circulate fluids through the clutches and valve bodies. As with engine oil, the transmission dipstick should register a range that the fluid level should fall between. It will usually only read correctly at operating temperature.
New transmission fluid was once red in color. The standard automatic transmission fluid ages just like engine oil, progressively getting darker as time wears on. New fluid almost smells sweet (compared to burnt, used fluid). Improper transmission fluid levels create common driveability problems that can easily be circumvented by keeping your transmission topped off with fresh fluid.