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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    2011 Prius
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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
    PriusCamper likes this.
  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
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