T&T: Multi-Viscosity Oil

[Mike Maurice]

I ran across some material recently that implied that SAE 15W-40 
contains more viscosity enhancers than 10W-30 considering what the point 
spread would indicate. For instance there are 25 points between 15 and 
40 but only 20 between 10 and 30. I gather that this little point 
difference of 20 or 25 has a LARGE impact on the amount of additive that 
it takes to provide the actual improvement in viscosity.

I assume that the reason why 15W-40 is more readily available is that 
the buyers have shown a preference and that such preference may not be 
based upon good technical grounds, but only some exaggerated assumptions 
that more is better. More viscosity range is better?

I am inclined to stick to using single viscosity oils with pre 2002 
engines. I suspect that we are going to see an increasing number of 
engines with real problems, even those where the owner has been 
religious about changing oil, but using an oil that is a poor choice for 
the age and use of engine.

If I could I think I would go for 40 weight, except in freezing temps. 
That I would roll the engine with the stop engaged so that it would not 
start. Hold till oil pressure reaches 20 psi or so and then let it fire.


Mike

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Capt. Mike Maurice
Beaverton Oregon(Near Portland)