2013 Toyota Prius — hybrid fuel economy dropped with no warning light — trying to narrow this down

Checked the easy stuff on the 2013 Toyota Prius and found one clue worth chasing before I book a shop. I'll poke at it this weekend.

Start with the test that can prove you wrong. A pressure test beats staring at a dry driveway if the 2013 Toyota Prius is losing coolant with no puddle. Save the big job until that test fails. Had a similar mess a couple years ago and that's what finally sorted it. Doing the boring step first on purpose.