Oil recommendations for high mileage 2009 Prius?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Bill Forest, Jul 5, 2026 at 5:24 PM.

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  1. Bill Forest

    Bill Forest Junior Member

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    Hi all,
    2009 Prius Touring
    175,000 miles

    Conventional 5W30 oil used in this car until 50K miles, when we switched to synthetic 5W30. All oil changes have been done by the dealer.
    Dealer used synthetic 5W30 until around 140K, when they started using 5W20.
    This car has occasionally use some oil, so I added Mobil1 5w20. (I know that some of you feel that it's a bad idea to add Mobil1 after the oil change with Toyota oil).

    I recently had the oil changed at 170K--they put in the usual 5w20 synthetic.
    Since then, I have had to add over a quart of Mobil1 5w20, as it was low.
    I am having the oil changed this week.

    A few questions:
    1. Some folks have said that it's better to use synthetic 5w30, as opposed to 5w20. Thoughts about this?
    2. Does the fact that my car is getting up there in mileage change which oil should be used?
    3. When the dealer changes the oil, should I purchase extra Toyota synthetic oil to refill with if it needs it?
    4. Any other recommendations regarding it using more oil lately? (It is not leaking oil, and I do not see an unusual amount of smoke from the tailpipe.)

    Thanks much!
    Bill
     
    #1 Bill Forest, Jul 5, 2026 at 5:24 PM
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    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.
     
    #2 Leadfoot J. McCoalroller, Jul 5, 2026 at 7:24 PM
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  3. BiomedO1

    BiomedO1 Senior Member

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    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....
     
    #3 BiomedO1, Jul 5, 2026 at 7:42 PM
  4. Tombukt2

    Tombukt2 Senior Member

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    I stayed with the 5:30 until 600,000 no reason to change it . Generally works perfectly no need to lighten anything up especially
     
    #4 Tombukt2, Jul 5, 2026 at 9:56 PM
  5. Mendel Leisk

    Mendel Leisk MMX GEN III

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

    IMG_4273.png

    no mention of “full synthetic”.

    Nor 0W20, for that matter.
     
    #5 Mendel Leisk, Jul 6, 2026 at 8:37 AM
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  6. ColoradoBoo

    ColoradoBoo Senior Member

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    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.)
     
    #6 ColoradoBoo, Jul 6, 2026 at 10:22 AM
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  7. BiomedO1

    BiomedO1 Senior Member

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    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
     
    #7 BiomedO1, Jul 6, 2026 at 2:09 PM
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