Each is designed for its own place in the vehicle. I would definitely avoid putting any Power Steering fluid in the crankcase. I would also avoid putting motor oil in the power steering. Power steering fluid is generally thinner than motor oil and would not be an advisable alternative to put in the crankcase. Now motor oil is thicker and can potentially damage components in the power steering with prolonged use. The detergents in motor oil may cause different issues with seals in the power steering, including leaks. On older vehicles the power steering generally called for automatic Transmission Fluid, but using power steering fluid in its place shouldn't hurt and may actually help.
You will screw your steering system. You need to flush steering system ASAP. And of course do not drive with engine oil in steering.
What fluid? Engine oil, transmission oil, power steering oil, coolant fluid, brake fluid.
I have a 1996 model, but I'm sure they're the same. The power steering fluid (as if you are peering into the hood) is on the right side of the engine, and closer towards the front of the engine. There's only two obvious places to pour fluid into on this side of the engine, and this one is the lower of the two places. One of them is the engine oil, which should say "Engine Oil Only", and the second is your power steering, which SHOULD SAY, "Power Steering Fluid".
The BMW 318i has a tank inside the engine that houses the power steering fluid. This tank is near the oil cap.
Power steering fluid is typically hydraulic or transmission oil. Drain the engine and change the filter. Replace the oil in the crankcase with the correct oil and amount. I don't believe it will damage the car but PS oil was not designed for use in a crankcase of an internal combustion engine.
Engine coolant fluid? Engine oil? Transmission oil? Brake fluid? Power steering fluid?
YES. your power steering pump is a hydraulic pump that pushes fluid through lines to make your wheels move. hydraulic fluid such as ATF or POWER STEERING FLUID is good for your power steering pump. it is a PUMP after all. OIL has the purpose of lubricating, and has very different qualities than hydraulic fluid. DO NOT put OIL in your power steering pump... put POWER STEERING FLUID or if you can't get power steering fluid AUTOMATIC TRANSMISSION FLUID will do...
Next to the oil filter inside the engine bay
No. Put in power steering fluid.
Brake fluid in the oil won't be much of a problem. It probably won't hurt anything, but to be on the safe side, just change the oil. In the power steering pump it will be harder to get out. You'll have to disconnect the high pressure line and let it pump out, then re-fill it with power steering fluid.
No problem
You could get an oil change as soon as possible to flush the system.