I may be wrong - but semi synth is for engines that don't like thicker oils such as a fully synthetic one. The differences are just in the quality in that mineral oil breaks down a lot quicker than synthetic.
Ta,
Graham
I see there are engine oils labelled "semi/part-synthetic". Are they any real benefit over ordinary mineral oils? Seem to remember reading somewhere about never mix synth with mineral - yet this stuff seems to be just that!
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