Oil pressure question...I promise it's not another "who likes what' thread!
Just found this on the internet, but I guess we can't believe everything we read there:
Oil weight, or viscosity, refers to how thick or thin the
oil is. ... Your
engine needs
oil that is thin enough for cold starts, and thick enough when the
engine is
hot. Since
oil gets thinner when
heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity
oils.
Viscosity index improvers make sure oil thins less, it does not make it thicker than when it was cold (my interpretation). Or maybe we are all on the same page. I could be mis-interpreting posts above in #31 and #33.
What do oil viscosity numbers mean? Learn about motor oil, synthetic oil and regular engine oils..
Ok, ALL engine oils are multi viscosity, but not all engine oils are multi grade. You have to get your head around that first. There is no such thing as an oil “weight”. There is an oil grade. The W in engine oil nomenclature is its Winter grade rating.
Viscosity is based on oil temperature. So any oil that is single grade (not “weight”) like an SAE 30 will always be less viscous at ambient temperature (what ever we say the ambient is...say...50 degrees) than it is a 212 degrees. This is Fahrenheit not Celsius.
A multi grade oil (just say 5w50) will gain viscosity with temperature. A 5 winter grade oil will be significantly LESS viscous at 20 degrees than a 20 winter grade oil.
ALL engine oils start out as whatever grade the winter grade is. A 20w50 oil starts out life as a 20 grade oil. To get the 50 grade (measured at 212 degrees F) the tribologist uses Viscosity Index Improvers so that 20 grade oil will act and flow like a 50 at temperature.
Also keep in mind that the bigger spread between the winter grade and the upper grade, the more viscosity index improves the oil has to have. The better the base stock(s) the easier it is to get a spread like 5w50. Some oils built with certain base stock(s) do not take additives very well, so the additive package is minimized. I won’t name brands, but any RACING engine oil that does NOT have a detergent/dispersant package, or a minimal package is not a good engine oil.
True, 100% synthetic engine oils are expensive, very expensive because the base stock(s) required cost more. Simple economics. A 10 buck bottle of “synthetic” oil most likely will use Group III base stocks, and they are NOT synthetic. I’ve posted this many times, but a lawsuit was brought and ended up at the Supreme Court and the court, as it mostly does, ruled that Group III base stocks are synthetic, when by the true definition of the word, they are not.
Engine oils also need other additives besides VI improvers. Detergents and dispersants keep sludge down and hold dirt and combustion by products in suspension until an oil change.
There are anti corrosion additives. There are additives like zinc dialkyl dithiophosphate are used for dry film lubrication.
And many more, and none of them are cheap.
The API testing standards are at best, minimal. Mostly, IMO they are essentially worthless. An oil can fall anywhere in the grade, and actually fall out of grade a number of times and still pass. That means if you pay for an oil that should perform like a 30 at 212 degrees F, but it falls out of grade and yet passed the test you actually have an oil operating as a 20 at temp.
Expensive engine oils, with quality base stock(s), full additive packages and superior VI improvers and dry film lubrication will be built on the high side of the grade, not the middle or the bottom.
That way, at temp the oil stays in grade. If you need a 30 and end up with a 20, you’ll certainly have lubrication issues.
There is much more to oils than grade, but grade is important.
