Re: H engine broke in Have oil question

Posted by Andy Martin on October 12, 2004 at 10:23:53 from (64.219.39.195):

In Reply to: Re: H engine broke in Have oil question posted by Redmud on October 12, 2004 at 09:33:03:

Without getting into too much detail, a 20w oil has a specified viscosity (thickness) which changes with temperature. It is described as a curve starting thick at cold temperatures and getting thinner with increasing temperature. 30w is thicker, 40w even thicker, etc. BUT hot 40w will be much less viscous (thinner) at 200 deg F than 20w is at 100 deg F. But if all three oils are at 200 deg F, 30w is thicker than 20w and is thinner than 40w.

Multiviscosity oils tend to act like the first number at low temperatures and like the second number at high temperatures. So a 20w50 does indeed act like 50w at high temperatures (operating range) but is similar to 20w at low temperatures.

For extreme duty you can stick with a single weight because after extended use a multiviscosity oil tends to break down and respond like the lower viscosity. So if you want to run 40,000 miles on conventional lubricant, stick with a single weight oil : )

I am a registered professional engineer in Oklahoma.

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