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5w30 A5 Certified vs 0w20 non-certified?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by alevinemi, May 16, 2009.

  1. alevinemi

    alevinemi Junior Member

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    All,

    I'm a new Prius owner and I have read a few threads here regarding oil weight. Basically, I glean that Toyota recommends 5w30, but 5w20 or 0w20 generally yield improved mileage. This mileage comes at a cost that the oil is not recommended and might not protect the engine as well.

    I noticed that Mobil1, and many other oils, are A5 certified in the 5w30 weight. This means they are certified for a higher level of fuel conservation.

    In contrast, the same Mobil1 oil is NOT ACEA A5 certified in 0w20 and 5w20 weights. (Source: The Motor Oil Evaluator: Motor Oil Comparison Software). A5 oil in these weights is hard to find.

    So, two questions:
    - Will A5 certified 5w30 give better or worse mileage than A1 certified 0w20 or 5w20?
    - What risk is posed by running 0w20 or 5w20 in my Prius vs. 5w30 weight oil?
    - Given I just bought my used Prius, is there an easy/free way to figure out what weight of oil is currently in it?

    -->Adam
     
    #1 alevinemi, May 16, 2009
  2. FireEngineer

    FireEngineer Active Member

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    The A5 rating means the oil in question is better than a 15w40 reference oil for fuel comsumption while meeting certain minimum shear characteristics. Mobil 1 5W30 is very close to a 5W20 in viscosity when new and this is why they can meet the A5 while maintaining the required shear characteristics. A 0 or 5W20 would probably be better, especially if it had a A3/B3 for higher shear wear.

    Many have used 0W20 in a Prius with good used oil analysis results, in particular Jayman and The Force.

    Only way would be with a used oil analysis, which will only tell you the current shear potential of your oil and you can see where it fits for viscosity. Impossible to tell the actual starting viscosity.

    Go ahead and use the Mobil 1 5W30, it's better than most dino oils, though it's not a full PAO synthetic. If you want better engine protection go for the European Formula Castrol Syntec made in Germany which is a 0W30. Better MPG for 0 or 5W20, though windy weather or wet roads will affect your MPG more than the oil will.

    Wayne
     
    #2 FireEngineer, May 16, 2009
    2 people like this.
  3. alevinemi

    alevinemi Junior Member

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    So, if I understand correctly, any 0W20 or 5W20 will probably meet A5 standard for fuel economy, but it may not do so for shear wear, thus failing the spec.

    I'm not a mechanic, but shear wear sounds like a bad thing - a synonym for "your engine won't last as long". Now, on a Prius, that could be the difference between a 500,000 mile engine or a 300,000 mile engine (both irrelevant, because the rest of the car probably won't last that long). However, it's still something that I am not willing to give up for 1 or 2 MPG.

    I haven't found any 0W20s that meet A3/B3 or A5/B5, but I have found two 5w20s that do:

    Wolf's Head Synthetic 5w20 meets A5/B5
    Lucas Oil Synthetic 5w20 meets A3/B4, thus should be as good on shear wear as A5, but for some reason failed the fuel economy part of the standard.

    Are these likely to give me better mileage than an A5-specced 5w30 like Mobil1, Pennzoil, or Amsoil?

    -->Adam
     
    #3 alevinemi, May 17, 2009
  4. spitinuri

    spitinuri Member

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    My understanding is that Toyota is moving most if not all vehicles to 0W-20 synthetic. They would have done so earlier except for the scarcity of it. I am using Mobil 1 OW-20 with excellent results.
     
    #4 spitinuri, May 17, 2009
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