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Originally posted by JohnBrowning:
Oil pressure is no more over rated then oil flow is. One positive thing about oil pressure
But its fairly safe to assume that all other things being equal, a lighter oil will increase flow per unit pressure applied by the oil pump.
A constant displacement pump will merely require more shaft work to move a thicker oil. A constant pressure pump will move more 'thinner' oil at the same pressure as less 'thick' oil is moved.
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is that oil pressure can be easily measured. No of these so called oil flow nuts have any idea how much volume of oil each part in their engine is receiveing at any given RPM. These same
Its fairly safe to assume that a thinner oil will give you at least an equivilant volume of oil (with lower pumping losses), or higher volume of oil (with similar pumping losses).
If the oil is capable of doing its functions without thermal decomposition, then its obviously suitable. In the past, thin oils didn't have the volatility, flashpoint, and oxidative resistance required, hence the 'thicker is better' wisdom was born.
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people have no means of dynamicly measureing flow either! Engine manufactures have strugled for years to try to determine volume of oil each parts needs at any given RPM and load and how much they are actualy getting. THeir is a reason that oil pressure is the gold standard for diagnostic purposes!
Sure, but its like UOA's. You can't compare a UOA from a Saab engine against a UOA from a Ford engine, and draw a conclusion about the quality or efficacy of a particular oil.
An engine will have a spec for a certain level of pressure running the manufacturer-specified lubricant. Thats a benchmark diagnostic value only -- not really useful for determining flow adequacy with a different viscosity of oil.
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Mtemp. versus high temps. For example if a 5W30 is safe to use at -25°F in an application then how is a 15W40 hurting anything at 80°F in that same application? Flow is meaningless with out pressure and pressure is not of much use if flow is restricted!
1) An engine won't run at an oil temperature for very long at -25degF. Maybe a minute or two at the most, on a -40degF day in the Arctic until the oil experiences some heating.
2) Its impossible to induce flow without pressure. That's just Newton's law of physics (F=ma), or whatever they call it in fluid mechanics.
3) The wisdom to use a thicker oil in an engine with a worn out oil pump (just to bring up pressure) may very well be flawed as well. An engine with a worn out pump, or worn out bearings, may very well be suffering from poor flow. Moving to a higher viscosity is actually counterproductive. Though I do admit, thicker oils probably have benefits in terms of ring seal, and can withstand sludge-induced hot-spots much more easily than thin oils. Not to mention the issue of leaks and oil control in components such as valve stem seals.