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5w30 or 0w20 in Gen 2 Prius in CO? Mixing viscosities?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Bill Forest, Aug 11, 2019.

  1. Bill Forest

    Bill Forest Junior Member

    Joined:
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    Vehicle:
    2011 Prius
    Model:
    III
    Hi all,
    09 Prius Touring
    103,000 miles

    I've had this vehicle serviced at the Toyota dealer since I acquired it at 18K. Every time I had the oil changed, they have used 5w30, and have been using full synthetic since 50K.
    Recently, I had the oil changed at 100K. I did not notice it at the time, but they put in 0w20 full synthetic. They did not mention this to me, I just recently noticed it as I was looking over the receipt for other info.

    Since this Prius does use some oil, in the 3000 miles since the oil change I have topped it off with Mobil 1 5w30. From reading other posts on PriusChat, I have gathered that it is OK to use either 5w30 or 0w20 (I live in Colorado, where the summers can be 100 degrees, and of course the winters will have below-freezing days.)

    Three Questions:
    1. Again, from reading other posts, it sounds like it is OK to mix 5w30 and 0w20 oils, as I have done by topping off with 5w30. Is that correct?
    2. Is 0w20 really good for 10K miles, or does it need to be changed sooner?
    3. In my climate, is it better to go with 5w30 or 0w20 for my next oil change?
    Thanks for your experience and advice!
    Bill
     
  2. srellim234

    srellim234 Senior Member

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    I did find this one here:
    Mixing oils of different viscosity...? - 600RR.net

    "All mineral oils are produced from the same basic petroleum feedstocks. Different oil viscosities will not separate or react negatively to each other because the base oil is molecularly the same. It's the different oil additive systems between brands that shouldn't be mixed - if you're concerned about the oil performing exactly how it was designed.
    Oil additives include:
    Anti-oxidants to prevent thickening at high operating temperatures.
    Pour point depressants which lower the temperature of wax coagulation
    alkaline materials to neutralize acids formed during combustion.
    Rust and corrosion inhibitors.
    Detergents to reduce sludge and varnish.
    Dispersant additives to hold contaminants in suspension.
    Extreme pressure additives to prevent metal to metal contact under high loads.
    Viscosity index improvers in formulating muilt-grade (viscosity) oils.

    The exact type and amount of these additives varies between brands and when mixed may not function as efficiently as desired. Different viscosities of the same brand oil will have different amounts of viscosity index improvers (polymers), but otherwise the additive systems will be the same.

    From the Chevron.com site:
    "Can I mix different viscosity grades of motor oils?"
    "Yes. It is always advisable to not mix motor oil brands, however, different viscosity grades of the same brand motor oil are compatible. Be aware that mixing viscosity grades will turn out a product that is different in viscosity than either what was originally in the engine or what was added."

    From Shell.ca:
    "If you mix viscosity grades such as a 5W30 low-viscosity oil and a 10W40 higher-viscosity oil, it is reasonable to expect that the resulting product will have viscosity characteristics which are thicker than the 5W30, but thinner than the 10W40. This change does not reflect incompatibility - it's simply a re-balancing of the viscosity characteristics. In all other ways, the product should work as expected. But there's absolutely no danger about incompatibility resulting from mixing engine oils," Miller says. "We've tested all of our grades and brands, and we haven't observed any problems."

    From Mobil1.com:
    "For our customers to choose a viscosity grade, we recommend they follow the engine manufacturer's recommendations as indicated in their owner's manual. There is no need to mix two Mobil 1 viscosity grades when one will do; however, we see no problem mixing different SAE grades of Mobil 1 Tri-Synthetic series motor oils.' "
     
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. This would be fine if you were using the same oil brand. If you are mixing brands, that might not be optimal practice.
    2. 0W-20 is recommended for 2010 and newer Prius and the oil change interval is 10K miles. Personally I am not comfortable with that interval and change oil at around 7K miles.
    3. If you change oil twice a year, considering the wide variation in ambient air temp, I would suggest using 0W-20 in the winter and 5W-30 in the summer.
     
  4. Bill Forest

    Bill Forest Junior Member

    Joined:
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    Vehicle:
    2011 Prius
    Model:
    III
    Thank you srellim234 and Patrick. That was a lot of good information. I suppose in the future, if I have my oil changed at the dealer, I will need to purchase some extra oil so as not to mix brands when I top it off.
    I appreciate all of your help!
     
    srellim234 and bisco like this.