Ever since the V8 horsepower wars in the mid 50's auto makers have designed their engines to run on the so called multi viscosity oils like 10W30, 10W40, etc. The engineers reduced clearances between moving parts to work with the thinner oils. They also printed in every owners manual a recommended list of various oils to use under different conditions. This is still being done today.
With a properly built engine that is in good condition the correct recommended light oil will provide the proper cushion to protect the engine from wear or worse.
Heavier than required oil will make the oil pressure gauge give a very impressive reading and many drivers think that is a sign of good lubrication when in fact the higher gauge reading is telling you that the oil is actually having a hard time going where it is supposed to be going.
Just imagine trying to stuff wheel bearing grease through a straw.
Unless the oil is subjected to extreme loading by the engine or might be thinned by fuel wash down as in some drag racing engines, most street engines have nothing to gain by excessively heavy viscosity. Even the NASCAR Cup cars are now running very light weight oils and many even use synthetics. Up until the rule change a couple of year ago prohibiting the use of a qualifying engine they ran 0W30 for qualifying in these 700 HP motors at 7000+ rpm. Of course they only had to last 3 laps.
Oil choice is almost as bad as argueing politics or religion, everyone is right at some point.
Mike G
