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Originally Posted by schmidtj
Thinner oil at high temperatures means more wear and tear on the engine. J
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GENERALLY, that statement is true.
But in reality it depends on the protection capability of the oil. The very best synthetic oils are designed with uniform size molecules so that they protect just as well in high heat as under other conditions. They are engineered to defend against thermal breakdown.
Quote:
Mobil Oil recently reported the results of simulated hot-weather
performance with its Mobil 1 synthetic as evaluated by a standardized,
grueling engine test known as the Olds III-D. In this test, an
Oldsmobile 350" V8 engine is run for 64 hours at a 100-hp load and 300F
crankcase oil temperature. This test is designed to measure an oils
ability to resist oxidation and evaporation (and consequent thickening)
at high temperature. (If it seems odd that oil would *thicken* at high
temperature, consider the analogy of heating a pan of cold syrup on a
stove. At first it would become quite thinner, but if left for, say,
several hours, the resultant evaporation would cause the syrup to become
progressively thicker.) In order to qualify for the American Petroleum
Institutes top "SF" rating, a motor oil must pass the III-D test. This
means that it can thicken to no more than 375% of original viscosity at
the end of 64 hours of continuous running. Mobil states: "To test the
extra stability provided by the Mobil synthetic oil, we decided to run
the III-D *for 128 hours*...double its normal length...and without oil
drain. The Mobil 1 synthetic easily passed the test under these brutal
conditions, thickening only an insignificant 20%. For comparison, a
high-performance premium conventional oil was tested under identical
conditions. That test had to stop at 96 hours; the oil had turned
solid. Another premium conventional oil forced the the test to stop at
112 hours, well before the end of the scheduled double length." Amoco
Conducted an identical double-sequence III-D test on its Ultimate 5W-30
synthetic; it also passed the test with flying colors, thickening only 18%
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So the thinner synthetics do perform way better at high temps.