Synthetic oil

  • #1
Molecules of conventional oil are of varying size and those of synthetics are of uniform size, so it seems illogical that synthetic oil would be superior to conventional for cold starting only, as the smaller molecules of conventional oil should be able to remain in tighter spaces that larger molecules may not fit into thus providing immediate and superior lubrication in those spaces upon cold starting. As synthetics are considered and proven superior to conventional oil in(most) tests regarding cold start engine wear, I would like an explanation.

Could someone expert in this explain exactly why synthetics are superior in just this one area when logic would make it seem not to be the case?
 

Answers and Replies

  • #2
brewnog
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I assume your question relates to reciprocating engines?

'Tight spaces' you might encounter in an engine are far, far larger than the largest molecules found in synthetic oil, so there are no issues with molecules being unable to get into small spaces. Also, synthetic oils are subject to the same viscosity standards as mineral oils.

The simple reason for synthetics being better lubricants is because they have been engineered to be better. Synthetic oils can give advantages in engines by:

- Maintaining viscosity at temperature extremes. Mineral oils can get rather viscous below freezing (meaning your cold-start protection suffers) and very thin (and sometimes decomposing) at high temperatures during heavy operating conditions (right when your bearings need it most).

- Maintaining chemical composition by having fewer compounds which evaporate over time and under temperature

- Higher resistance to thermal breakdown and oxidation
 
  • #3
Oil viscosity

As you seem to know what you are talking about...what process and/or ingredient(s)makes oils differ in viscosity? Is it chemical, physical or a catalystic process? Answer as detailed as possible please. Thanks.
 
  • #4
brewnog
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I suppose synthetic engine oil is made in the same way as synthetic fuel through some kind of Fischer Tropsch process (which is a catalytic process converting CO and H2 into various hydrocarbons), with the viscosity being controlled by using blends of different resulting oils. More than that I do not know.

I presume that the viscosity of mineral oil is determined primarily by the fractional distilation point, but also by the additive packages introduced.

I'm sure there are some great websites out about this stuff. Have a look at the Mobil and Texaco sites.
 
  • #5
About synthetic lubricants

I recently posted an http://kissaneasylum.typepad.com/synthetic_lubricants/2007/12/the-true-measur.html" [Broken] that may answer the questions you have posed
Hope it's helpful
 
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