Oil Viscosity and Oil Change Intervals

Discussion in 'Gen 4 Prius Main Forum' started by Deogratias, Oct 13, 2021.

  1. Deogratias

    Deogratias Member

    Dec 17, 2016
    2016 Prius
    I recently started doing my own oil changes and basic maintenance on my 2019 Prius after my local dealers all started experiencing staff shortages and the appointment times became untenable. As a happy side effect, I'm now learning a lot more about my car and automotive maintenance generally.

    I notice that the owner's manual specifies that 0W-20 oil "can" be used on a 5,000 mile oil change interval, but that 0W-16 is preferred and may be used with a 10,000 mile oil change interval. Confusingly, the manual also states that a higher viscosity "may" be better in extreme conditions or at high speeds.

    I live on the Gulf Coast. It gets pretty hot in the summer, and rarely gets more than a little chilly in the winter. I drive about 20,000 miles per year, but almost all of that mileage is done on a handful of very long road trips at 70+ mph (last month, I spent over 3,000 miles on a road trip and less than 100 miles running errands near my home).

    Does anybody have a strong feeling about whether 0W-20 (or some unspecified higher viscosity?) might be more appropriate than 0W-16 for long road trips in the Deep South? My concern is that a 5,000 mile oil change interval with my driving pattern would basically mean throwing away brand new oil after each road trip.
    Mambo Dave likes this.
  2. Georgina Rudkus

    Georgina Rudkus Senior Member

    Sep 15, 2018
    Taylors, SC
    2012 Prius v wagon
    5,000 mile oil is NOT brand new oil. It is oil near the end of its life. Personally, I do not believe in 10k oil changes. Oil and filters are cheap when compared to replacing, the head gasket, the rings or worn out cylinders. 5k is a good compromise.

    I recently changed oil at 6 months and 1,800 miles. The oil was already dark and dirty. My money was NOT wasted.

    The car today, for the sake of low internal friction to increase EPA mileage, have low expansion pressure oil control rings. Any varnish or sludge on the rings will cause them it stick in their channels sooner than later. The same varnish, dirt or crud will also clog the narrower oil passages in the newer engines. The abrasive particles carried in the oil will wear the parts sooner than clean oil.

    Oil also acts as a coolant for the engine. Varnish and crud buildup will act as an insulator and impede heat transfer and cooling.

    The secret to engine longevity is clean oil.
    #2 Georgina Rudkus, Oct 13, 2021
    Last edited: Oct 13, 2021
    Doug McC and Ozark Man like this.
  3. alanclarkeau

    alanclarkeau Senior Member

    Feb 24, 2016
    near Brisbane, Australia
    2016 Prius
    My theory - depends on how long you want to keep the car. If it's a 5-7yr, 100000k investment - use the cheaper option. If you want to keep if for a million miles - pay the extra.
    Mambo Dave and Georgina Rudkus like this.