A friend of mine just finished rebuilding a 22RE for my 4Runner. I had him use Mobil Clean 5000 5w30 for the break-in. I provided enough oil for three complete changes: (1) After initial start up and short run, (2) Next OCI of length TBD of about 500 miles, and (3) Final conventional OCI to 2,000 miles. There was a slight issue with the oil pressure so he may have used an extra round of oil during the initial break-in process. I'm considering running Mobil 7500 (blend) between the 500 mile and 2,000 mile synthetic swap. I have heard that using synthetics can be "bad" or at least increase the break in period from reduced friction, does this really only apply to Group IV oils? Is the Mobil 7500 a blend using some PAO, only Group III, or nobody knows for sure? Part of the reason I am interested in using the 7500 is I have a little sitting in my garage that I have no other use for and I don't like to mix.
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