Contrary to popular opinion a full synthetic 0-30 will give more than enough protection for any engine that is not running full power in the desert. The 30 means just that. It is a full 30 weight at 200+ degrees. If you check the specs on that oil you will find that it is better than a lot of standard 15-40s plus you get the benefit of the 0 weight which is a plus on start up in any climate. It will work just fine in your vintage chevy. Until the advent of multi-grades I ran straight 10 in a chev 350 and it had 200k before the body rusted off and the engine was all original and still did'nt burn oil. Many a engine has been ruined unknowingly by using heavy oil.

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82 300SD 100K
91 Caprice SS
92 Jetta TD