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I have to partially agree with you that pressure is not flow. Pressure is the force that moves mass. I thought about this for awhile, and I guess the reason why I like to see oil pressure is that I know that I have enough pressure to cause adequate flow to the parts requiring it (valve train for instance). If I am pumping enough oil to get pressure, the parts are getting lubed (barring a malfunction). If I have no indicated pressure, I could have 20 gpm but I wouldn't know it. But you still have to consider the case of Mobil 1 where some diesel engine mfgrs (Cummins, Mack, D.D. Caterpillar etc) would allow 10-30 in their engines but others wouldn't. So, what is the mechanism that prohibits it's use. Is it the oil film strength? Or is it the fact that the more viscus the oil, (as you said) the more resistance to flow and hence the indication (to the operator) that the engine is being properly lubed. I have Chev, Ford, and Dodge, trucks. All V8's with low mileage except the Ford. The oil pressure on the Chev is all over the place (as I have deliberately noticed in other Chevys). I use Delvac 15w-40 and Mobil 1 15w-50 to have at least 20 psig of oil pressure at idle on a trip in the summer. The Dodge sits on 50 psig and doesn't move regardless of all the elements except engine off. The Ford (with at least 165k miles) sits just above mid-scale (whatever that is) and doesn't move either. Different people have their own opinions, but mine is that GM's engines are not as rugged as Ford and Mopar. I can't help but think oil pressure is a contributing factor. I have been told that different engines use different type lubrication systems. Some use low pressure high flow, and others the opposite. Maybe the Chev is the former and the others the latter. So the saga goes on and maybe all this hype is all for not. Maybe the real answer is keep the level up and clean oil and all of it will work. Enjoyed the exchange. Mark
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