No matter what the viscosity, warm oil flows easier then cold oil.  Warm oil
is not thicker than cold oil.  As for multi-weight oils, there are 2 answers.
 Standard 20-50 oil is 20 weight oil that is treated with polymers to not
lose its lubricating quality at higher temperatures.  The polymers degrade
with use, so the oil gradually loses some of its upper temperature
protection.  Synthetic oils are natural multi-weights, and do not lose
viscosity range with use.

In a message dated 11/13/99 6:40:34 PM Pacific Standard Time,
wdavidson@THEGRID.NET writes:

<< Okay, I'm confused about something....
 My understanding is that when using multi viscosity oil like 20 - 50 that
 when the oil heats up the oil actually gets thicker (50) and when the oil is
 cooler like on start up the oil is thinner (20). Is that correct? If so, why
 does oil seem to be thinker when it is colder... like that's why I warm the
 engine up a little before doing an oil change... so it will drain out
 faster.
 Okay so where is my thinking wrong?
 Thanks,
 Bill
 90 Westy Syncro
  >>