It is generally not recommended to use a power washer to clean the engine and transmission of a car. While power washers are effective at removing dirt and debris, the high pressure of the water can cause damage to sensitive components and electrical connections.

Water can seep into the electrical connectors, leading to malfunctioning sensors or even electrical short circuits. Additionally, power washers can force water into areas where it shouldn't be, such as the intake or exhaust system, which can cause damage or corrosion.

Instead, it is recommended to clean the engine and transmission by gently spraying a degreaser or engine cleaner onto the components, allowing it to sit for a few minutes to break down any grime, and then rinsing with a hose or by using a low-pressure water source, such as a spray bottle.

It's important to cover sensitive electrical components with plastic bags or waterproof covers before cleaning. Also, avoid spraying water directly onto the alternator, battery, or fuse box.

If you are unsure or uncomfortable with performing the cleaning yourself, it is best to consult with a professional mechanic who can safely and effectively clean the engine and transmission for you.