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Originally Posted by Tomaz
I've never heard of the "no replacement for viscosity" claim. If this is absolutely true, I'll change to a higher viscosity oil. Is there a study that verifies this? I had always imagined there was a trade off as higher viscosity oils flowed slower and put additional stress to the oil pump. Further, I had heard that modern engines were manufactured to tighter tolerances and therefore, needed lower viscosity oils.
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Viscosity is what keeps the engine parts from contacting each other through "hydrodynamic" lubrication (like hydorplaning tires). If the fluid film breaks down in a high heat situation due to a lack of viscosity moving parts will contact one another with serious consequences. Anti-wear additives help to minimize damage but simply cannot replace viscosity.
My response regarding Mobil 1 15W-50 was directed to the original poster of this string who stated the following: "Also, I live in the
Texas heat...is 5W-30 safe or should I go with 15W-30?". In colder climates a lower viscosity oil is necessary for engine start-up, but in the "Texas heat" the 15W-50 is the best recommendation AND can be used year round in the Houston area.