5th gen prius 0w8 vs 0w16 discrepancies

In the early days; 0w8 was hard to come by and most dealerships dumped 0w16 in.
My advice is if the car engine was broken-in with 0w16, stick with it. The same engine in other countries go as high as 5w30. Switching to thinner oil after break-in may cause issues (ie. higher engine oil burn between oil changes). Some OEMs claim that burning a quart every 5K miles is acceptable - I don't!!! That much oil burn would kill the CAT, just outside federal warranty. Then again, that's all the dealership is concerned with - getting past the warranty period.

Just my two cents.....

 

The 2026 engine isn't 'identical, of course'. How can you conclude that? Do you think a production line that can change which oil they put in and which oil sticker they apply can't change anything else?

There is at least one potentially related change I've spotted in the technical manuals, which is that the oil level sensor was deleted in July 2025. Maybe it didn't like 0W8?

(Another change at the same time, probably unrelated and due to new CARB rules for 2026 models, was the removal of charge mode for American PHEVs.)

The Prius oil change to 0W8 happened worldwide at the same time, aligned with those July 2025 production changes. Whoever said European cars were using 0W8 before was referring to other models.

 

And Gen 4 also switched from SAE 0W-20 to SAE 0W-16 in the 2020 model year.

Did the engine change in Gen 4 or Gen 5 that allowed a lower viscosity grade? Snowball-in-hell chance. OEMs don’t spend that much thought on minute details of engines to recommend an oil viscosity. They make general tests, even on a slightly different engine, and then make recommendations for similar engines.

What happened was basically that they determined that 0W-8 was safe after new tests, and then they changed the oil recommendation after that determination. You can use 0W-8 for earlier Gen 5, yes, without any problems.

 

Not sure what that tech manual is, but the 2026 owner's manual still makes mention of it on page 482.