10w30 vs. 10w40

From: Rader (rlr@bbt.com)
Date: Fri Feb 20 1998 - 10:24:18 EST


> One last one, would 10w40 be a better choice than 10w30 for this engine in
> the summer? I used to have a 440 charger and 10w40 was recommended in the
> summer.

> You will actually make more
> horsepower with lighter oil. Stick to 10w30 UNLESS you live in the
> Arizona desert!

  With multi-viscosity oils, the lower number is the base viscosity. The
higher number is a measure of how the oil will act at higher temperatures.
Under higher temperatures, the oil does not get "heavier," it's additives
simply allow it to provide the same protection as an oil of the higher number's
viscosity.

  10w40 is not "heavier" than 10w30. 10w40 has more VI extender polymers
in it's additive package than 10w30, allowing it to protect like a 40SAE oil
under high temperatures.

  I doubt you would experience any horsepower differences at all switching
between 10w30 and 10w40 oils. However, you would experience horsepower
differences switching between 10w30 and 20w50, because the base oil _is_
heavier in that case.

  Like I said before, stick with the manufacturer recommendations.

  Ron



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