A Exhaustive Primer On Motor Oil

[Robert J. Alder]

Didn't see an appropriate Topic Forum in the "General" category so I'll post this here in vintage section where there is a "General" bucket.

The following is a a link to a fellow's exhaustive discussion on motor oils -- specifications and resulting pressures, flows, etc. Sure a lot in the article I didn't know about motor oil. A LOT!

Should be of interest to all racers and will, no doubt, generate some interesting comments.

http://www.ferrarichat.com/forum/faq...tor_oil_basics

[Dave Welsh]

Mmmmm, it appears that Ferrarichat.com is borrowing something from Bob.

http://www.bobistheoilguy.com/cms/in...tpage&Itemid=1

[Robert J. Alder]

Indeed. A fair amount of non-disclosure and [FONT=&quot]plagiarism [/FONT]by one of these fellows.

[smbrm]

Didn't see an appropriate Topic Forum in the "General" category so I'll post this here in vintage section where there is a "General" bucket.

The following is a a link to a fellow's exhaustive discussion on motor oils -- specifications and resulting pressures, flows, etc. Sure a lot in the article I didn't know about motor oil. A LOT!

Should be of interest to all racers and will, no doubt, generate some interesting comments.

http://www.ferrarichat.com/forum/faq...tor_oil_basics

Indeed, engine oil is a topic that has much more complexity than most of us truly appreciate. They really are magic elixirs. They are fluids that get much less attention and thought from users than specialty coffee, yet they deliver amazing levels of performance for the applications that they serve.

Generally this is a very good discussion of the subject.

There are several points I would suggest require clarification. And since I do not want to deliver an equally lengthy reply I will only discuss a few that I think significant:

He suggests that Synthetics do not have VI Improvers.

This is not true. It may be true for some, but most synthetics engine oils that we can buy commercially use some VI improver, and perhaps less depending on the Viscosity index of the synthetic base oils used. They may also use more expensive shear stable VI improvers that offer better performance. The wider the span of the multigrade eg. difference between the winter "w" number "10W" in 10W-30 and the high temperature number "30" in 10W-30, the more VI improver. Formulators like to get as much VI as they can from base oil because it does not shear as VI improvers do, however VI improvers are as common in synthetic multigrades as they are in mineral oils. However the formulations may be quite different to deliver their viscosity characteristics.


Re: Racing Oils "...These oils generally do not have detergents..." I would suggest that this is not correct! They may have less, but I know from experience that none is not an appropriate description. Engine oils, truely optimized for racing, will not be the same as passenger car engine oils because from an optimal perspective the needs are different enough that there are performance advantages that can be designed into the lubricant.

Re: ".....Motor oil becomes permanently thicker with exposure to northerly winter type weather. This is more of a problem to mineral based oils. Waxes form. This is why it is a bad idea to even store a bottle of oil in a cold garage. It goes bad on the garage self just because it is exposed to the cold....."

While waxes do form if the oil is cooled below its cloud point, and especially below the pour point, this is not irreversible once you warm it back up and with agitation the waxes can go back in solution? In my experience I have never heard this description before and doubt its significance for appropriately formulated engine oils.


Re:"....There are no start up issues so pour point depressants are not added that minimize the thickening with cooling in gear oils....."

Also not true, even for synthetics. Gear oil do use pour point depressants and some even Viscosity index improvers. Gear oils based on high viscosity index base oils may use less than those with lower Viscosity index, but none is not an appropriate description. Pour point depressants modify any wax that forms to make it less prone have a dramatic effect on oil pumping viscosity at temperatures near that where wax crystals start to form. Every lubricant has a pour point and once you get to it, the oil does go solid. Pour point depressants can lower the temperature at which this occurs and can help formulate oils that have a greater low temperature safety factor. Cold starting viscosity is also important characteristic of gear oils their thickness can contribute to power and fuel economy losses as part of the overall driveline.

In fact pour point is really irrelevant to an engine as they won't start at all if the oil is below its pour point! What is more relevant is low temperature pumping performance because this does impact oil flow rate during critical low temperature startup. That is why the viscosity grading system is designed to ensure that for a given oil grade, the oil will pump at 5 degrees below its designed starting temperature. Each grade, 0w-xx, 5W-xx, 10W-xx has improved starting and pumping temperatures over the next higher grade. There is also room for improved performance within each grade as the viscosity requirements cover a range. Oils can formulated at the thicker or thinner end of the range to create performance differences.

Re:"...High pressure helps to keep metal parts like the bearings out of contact with each other (scuffing)...."

Partly true, but not totally as it is not the pressure that the pump produces so much as the hydrodynamic pressure that is created by oil in the rotating bearings and sliding contacts that keeps surfaces apart. How much separation you get is related to many things including load, temperature, oil viscosity, bearing dimensions and speed, to name a few. The oil pump keeps delivering a supply of oil to those contacts and based on pressure and flow and the other factors contributes to maintaining oil in the contact areas to ensure hydrodynamic lubrication is maintained. Maximum flow with just enough pressure to maintain the needed flow rate would be ideal as you would always be feeding the needed contacts with adequate oil to create hydrodynamic lubrication and appropriate film thickness without the power loss from creating more pressure than required.


As I said not wanting to deliver a long response I will end here.

The author is absolutely correct, however, that there are important performance benefits to be had from using lower viscosity engine oils in our passenger cars and in racing.

cheers