Transmission fluid is a vital part of your vehicle's transmission, and it needs to be replaced on a regular basis to keep your car running smoothly. However, if you're in a pinch and need to replace your transmission fluid but don't have any on hand, there are several substitutes that you can use.
One option is to use motor oil in place of transmission fluid. Motor oil is thicker than transmission fluid, so it may not work as well in cold weather. However, it will still lubricate your transmission and should get you by in a pinch. Another option is to use power steering fluid. Power steering fluid is thinner than transmission fluid, so it may not provide as much protection for your transmission components. However, it will still lubricate and cool your transmission, and it's unlikely to do any harm if used temporarily.
If you're really in a bind and can't find either motor oil or power steering fluid, you can also use automatic transmissions fluids from other vehicles. These fluids are typically compatible with most transmissions, so they should work just fine as a temporary replacement for your own vehicle's transmission fluid. Just be sure to check the compatibility before using this method.
In short, there are several substitutes that you can use for transmission fluid if you find yourself in a bind without any on hand. Motor oil, power steering fluid, and other automatic transmissions fluids are all viable options that will work temporarily until you can get your hands on some proper transmission fluid