Something to keep in mind and pay attention to is the weather.

In Portland you are at sea level. The mountains are higher. Its typical in late October to get snow at Government Camp mountain pass on US 26 by Mt Hood--part of a loop you could do going out I-84 to Hood river then south then west on US 26 taking you back to Portland. For Government Camp you can turn off and head up the mountain to Timberline Lodge.

Another option as a day trip on Friday is a loop where you head south on 99W through wine country then cut over to the coast and drive north on 101 ending at Cannon Beach around sunset.

Another option is to drive and see St Helens. In late October is when the main visitor center closes for winter. You could go morning to hear then afternoon to Canoon beach for sunset before coming back to Portland.

If you are going to stay in downtown look at Friday as the day you do a day trip where you rent a car for the day.