Originally Posted by paulri
Interesting question. Since the answer appears to be yes, then why is this the case? Is it that the engine has to work harder, to push through a thicker oil? Or is it that a thicker oil will absorb heat better? If I understand Mad Hatter correctly,
he is saying that it is the first--that the engine has to work harder?
Tolerances determine the ideal viscosity..too thick of an oil and starvation and drag (resistance) can be a problem; too thin of an oil and oil film thickness can become an issue in preventing metal to metal contact.
The thicker the oil, the harder the engine has to work to push that oil through the engine, filter etc. This (engine working harder) will cause an increase, on some level, of engine temps. This is also why high viscosity oils are not designated resource conserving (increased fuel consumption). In addition, higher viscosity oils have larger molecules and when an oil ages and the lighter molecules burn off you have a high(er) concentration of those larger molecules (think sludge) that can cause wear in areas of tight tolerance (think bearings). Now synthetics are designed to have uniform molecules that better withstand thermal breakdown as compared to mineral oil. The higher the quality of the synthetic base oil, the more uniform the molecules are and better thermal stability. I believe that the same holds for the type and quality of the viscosity modifiers used.
I'm just a regular Joe trying to relate stuff I've read, so if I've got something wrong please chime in.
There's a lot out there on oil drag but here's some stuff that you might find useful..
Viscosity
Viscosity 2