I am the original owner of my 2000 4 Runner w/ 3.4 L. v-6. It currently has 325 k. miles. Since day one I've ran full synthetic Castrol or Mobil 1 along with " PROLONG " motor oil additive available @ Auto Zone for $20.00.
Religiously @ 5000 mi. I add 1/4 qt.
then change @ 6000 mi.
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