Has anyone noticed?

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Aug 12, 2003
south texas border
I have noticed that the viscosity at 100C for many good quality oils which are group 2+ or better is lower for the 10w30 than the 5w. Doesn't seem to hold true for cheap oils. Example: havoline synthetic 10w is 10.1 and 5w is 10.5. Anyone know why a supposidly higher viscosity actually shows thinner? And does this mean that it would be better to substitute the 10.1 10w for a 5w20 than a 5w30? since the vis is lower? Just thought it was interesting.
I believe they formulate it this way on purpose. They know that their conventional 5w30 viscosity will shear back quicker than their 10w30, so they design it to be thicker at 100c when new so that somewhat compensates for the thinning out.
the purposely making it thicker makes sense, but not all oils do this...I have a honda civic 2002 and been running amsoil 5w20. it gets beastly hot down here (109) last week. and in one of the other forums a gentleman mentioned that honda 5w20 was 9.8 at 100 in vis if that is true I don't see why I can't run the havoline syn 10w30 at 10.1 vis. not much difference me thinks. that thought was what got me started. And I agree that havoline is been pretty good for a while...don't know it its the cleanest but it seems to keep the cars running good long time. thanks for the input
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