heres something i read recently on a tacoma forum.....

in the v6 1grfe engines, toyota actually says to NOT use synthetic oil. it was in a toyota bulletin or document someone posted & specifically said these v6's should not use full synthetic... not sure why, but it was pretty clear toyota said it for some reason.

anyone heard that before or seen the document too? maybe its seepage or leak related?

im a full believer in synthetic oil being better than normal oil... but theyre are some engines that dont like it or not designed for it.. example is older v8 engines with flat tappet lifters/cams, the lifters wont rotate in their bore like they should due to the decreased friction from synthetic. & older v8s like that with older tech gaskets & high miles can definitely have leaking issues on synthetic.

just something to reasearch & think about for the v6 & synthetic oil.