Do you recommend using a thicker oil on a 05 scion xb with 31,000 miles when getting an oil change

l would not increase the weight of the oil unless the engine uses more than a quart of oil in 3000 miles and/or the oil pressure is below normal. 30,000 miles is a very young engine unless it has been abused. Always change the oil every 3000 miles with petroleum oil or about every 6000 miles with a good synthetic oil. High quality synthetic oil cost more, but it goes further.

No. 31k is low mileage for that vehicle. Follow the owner is manual suggestions.

Toyota makes great engines, At about 50,000 l would start to up a high end synthetic oil. That well help the engine when it start getting older.

But your only at 31K, l would not worry about putting and thing new in. Just do what your manual says and you will be fine.

Absolutely not. There is no reason for it, and besides, you have variable valve timing, which could be affected adversely with thicker oil in a cold climate (it is operated hydraulically by oil---so thicker oil, less flow, no valve timing).