Oil recommendations for high mileage 2009 Prius?

For a machine like that, the game is 99% about keeping enough oil in it and 1% about what kind.

The thing that changes the most with high mileage is how fast you use it.

How fast you use it tells you how often you need to check it and top it up.

Don't be late.

If it were mine I'd be using whichever store-brand 5W-30 I could get cheapest.

 

I believe your OEM manual called for 5w30 full synthetic oil at 5K mile intervals or every 6 months. You've run the car on 5w30 for 140K miles, then went to a thinner stock oil - seems your oil burn question has answered itself.
Go back to the 5w30 oil and the problem should rectify itself. The advertised "high-mileage" oil is formulated to burn less oil; assuming your putting the correct weight oil in your car.

IMHO; a dealership that doesn't follow the OEM recommended maintenance, parts and service - makes me think; what other corners or recommendations are they ignoring? If they refuse to put full synthetic 5w30 oil in your car; Take your business elsewhere....

 

I stayed with the 5:30 until 600,000 no reason to change it . Generally works perfectly no need to lighten anything up especially

 

Seeing is believing? This is all I’m seeing, in Toyota USA’s publication Owner’s Manual, for 2009 Prius:



no mention of “full synthetic”.

Nor 0W20, for that matter.

 

I've always used full synthetic oil in all of our cars. (I, currently, maintain all 8 of them....6 Toyota's, a VW, and a Hyundai)

For the older ones (we have two 2008 Toyota's) I switched them to Valvoline Restore and Protect (full synthetic) a couple of years ago. I switched the GDI engine in the Hyundai to it when it first came out and noticed the oil VERY black coming out after 3,000 miles the first two oil changes but, now, it's a dark golden, brown....so that's encouraging. (The Hyundai and VW get changed every 3,000 miles, the Toyota's seem okay with every 5,000 miles or 6-months...whatever comes first.)

I never play around with viscosity...whatever the oil is on the filler cap is what they get. (VVTi gears in the Toyota's are sensitive to viscosity and it, actually, changes when the oil gets old so that's why 10,000 mile oil changes is NOT a good idea.)

 

My old 2012 Prius C started burning a good amount oil around 80K miles. I didn't know about the low tension piston rings at the time, so I went from the OEM specified 0w20 to 5w20, high mileage formulation. That decreased my oil burn by 75% and I no longer had to add oil between oil changes.

YMMV