No problem dude.
Just pains me to see people running 3,000km/3month oil change routine without really thinking about it. It's like changing your underwear 3x a day because someone told you to.
Waste of precious oil resources (and money too!)
If anyone decides to go do a Used Oil Analysis (UOA), things to note are the viscosity (make sure the oil hasn't sheared out of its range limit.)
Refer to the SAE (Society of Automotive Engineers) chart below, for viscosity limits for oil weights. The first column denotes weights. For example, the 30, in 5w30. The 40, such as in 10w40. This is a chart for 100 degrees C temperature. (As you might know, viscosity changes with temperature. SAE likes to use 40C and 100C as datum temperatures for oil viscosties.)
For example
looking at the S2000's UOA in the above post, we see that the viscosity at 100C is at 11.22 centistokes.
According to SAE regulations this oil, amazingly after 50,000km still has the viscosity properties of a 30 weight oil. There are some UOAs that show a drop on operating cST below 9. This means the oil has 'sheared out of viscosity'. It's a common problem for an oil that's been left in too long. Cars with timing chains instead of timing belts also tend to shear oil more easily. Sometimes 5w30 oils shear to 5w20 levels. That's not acceptable for say, a turbo application like the RDX, which calls for a synthetic 5w30 oil that meets the strict HTO-06 spec.
Another variable to note is the Total Base Number (TBN). Most modern oils start at TBN number of around 7-10, Amsoil even 12. The number then decreases non-linearly to 0. A TBN of 1 is considered too spent. In the example of the Miata above, it was rated a 3.3. It probably could have gone a couple thousand more KMs. The higher quality oils, such as the ones from a Group IV or a Group V basestock will tend to have higher TBN numbers.
Quick 101 on Oil: Oils are made up of Basestocks and Additive Packages. Basestock are the "meat" of the oil, where the additive package give the basestock different desirable properties by adding components, such as detergents, friction modifiers, rust inhibitors, anti-foam agents, pour point depressants, dispersants, and anti-oxidizing compounds, just to name a few. The additive package ranges anywhere from 1% to 20% of the oil volume.
Basestock Groups:
Group I - Mineral oils - cheap, outdated conventional oils may fall into this category.
Group II - Most modern conventional oils (dino) fall under this category.
Group III - Made from a process called Severe Hydrocracking or Severe Hydroprocessing a Group II basestock. Essentially super-refining the Grp II basestock to nearly have Group IV properties to simulate synthetic oil bases.
Group IV - PAO or Polyalphaoloefins. Made from men in laboratory coats. The truly synthetic basestock.
Group V - Made up of Esters and polyolesters. Another creation of men in laboratory coats. Group V isn't usually used a a pure basestock, but mixed with other ones to give it more desirable properties.
Hint: Mobil1 5w30, Castrol Syntec (Except German Castrol), Pennzoil Platinum all fall under Group III category. (They technically aren't TRUE synthetics, but are allowed to be marketed as such) Only Amsoil SSO/ASM and German Castrol are known to be of Group IV basestock (completely synthetic). Some other grades of Mobil1 such as 0w20 and their 15w50 are speculated to be synthetic blends, containing only some PAO.
So anyway, back to the UOA, all the other metals test show different stories such as air filtration problems (a high Silicon number would show).
The 3rd thing to look out for in a UOA is the fuel percentage. A high percentage of fuel in the oil (roughly >3% (due to the blowby from the piston rings) is a good indicator that the oil will need to be changed more frequently than a non-fuel diluter. A common example of a fuel-dilutor engine is the 3.0L V6 in the newer Accords.
Lastly, the other things to note is the insolubles number. A high insolubles number means the oil filter is not doing it's job well. Contrary to popular belief, the oil filter doesn't "clean" the oil in the sense that it turns the color from black, back to the original golden brown color (or purple in Royal Purple's case, or Green, in German Castrol). It's job is to filter out insoluble particulates that the oil itself cannot encapsulate(dissolve and hold in a suspension).
Just as there is no best car, there is no such thing as a 'best' oil.
Hearing about people putting Motul 300V Synthetic Oil in their 1.5L stock Civic (but it has a WING! and VTAAK!) which is used to get groceries is rather pathetic to point of
.
The ideal oil for your car depends on many factors, such as:
1. What kind of vehicle you have
2. What your owner's manual says -- not just viscosity, but certifications (look for acronyms like API SM, ILSAC GF-4, etc.) and their recommended change intervals as well
3. Where you live, the seasonal temperature change.
4. How you drive (easy? hard? fast? slow?)
5. What your daily drive is like (short trips? long trips? city? highway?)
6. Whether your car has any known problems
7. Whether you want synthetic vs. conventional
8. How long you'd like to go between oil changes
Going for a pricey synthetic may not necessarily be the smartest choice depending on the variables listed above.
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