Originally Posted By: Quartz
Originally Posted By: Quattro Pete
It represents a range of kinematic viscosity that an oil will have at 100 deg C, according to sae j300 table.
Uhh..... in english?
The "grades" that we know and love (well some do, I don't) evolved from trying to define physical properties that related to engine operation.
Here's a 1923 version of j300.
The viscosity measured was literally the time for a given volume of oil to flow under gravity through the apparatus. The grade names were related to this time...it also explains why they had to fix the 20s recently.
Go
here to see how SUS convert into Cst.
If you look at the 020 and 030, it was know that some oil sources had better properties at cold temperatures than others...those two, while having the same "warm" performance, had much better pour points than others, earning a special classification.
Later, the grades were broken into Kinematic and Dynamic viscosity ranges, like the J300 table on the right. They had broken performance into two ranges, the "W", which originally DID stand for "Winter" is the performance at the extremes of the oil's ability to flow and pour, and the KV100 range, which is what the oil does at 100C.
A monograde could theoretically be any of the horizontal lines across the chart. Could (and can commonly get) an oil that is a 10W, or an SAE20, SAE30.
If it met both requirements, it could be labelled as a "multigrade", the strangest of which was 20W20, which meant that it was essentially a 20, but it also had the cold temperature performance of a 20W.
A 20W50 means that the oil meets the cold temperature performance of a 20W, but the high temperature performance of a 50.
Strategies included the use of PPD to lower the "W" rating, and Viscosity Index Improvers to improve the 100C performance.
The page on the left shows a later version still in the evolution of the standard.
* The "W" now references CCS (Cold Cranking Simulator), which reflects the ability of the engine to crank with that oil in the bearings and piston skirts at that temperature.
* The "W" now references Borderline Pumping, which is the ability of the oil to flow into the pickup tube, and feed the oil pump.
* now has HTHS (High Temperature/High Shear),
The HTHS was included as it had become obvious that some of the early "multigrades", while promising engine protection in their grading, weren't protecting rings and bearings. They found that under high shear rates (like in bearings and piston skirts, cam lobes etc.) that the polymers were "stretching", or flattening out, and the viscosity in those components was reduced by 25-30% *or more).
The HTHS minimums were essentially those that were at the top of the grade lower.
30 had a minimum HTH2.9, while a 20W20 monograde would have that.
40 had a minimum of 3.7, while a monograde SAE30 would be in the 3.4-3.6 range. The 0W, 5W, and 10W 40s only had to meet 2.9, same as the 30s, reflecting what a stretch early multigrades were.
Most recent version has more changes.
They "fixed" the 20 grade, as the original time based measurement left a massive spread of KV100 for the 20s.
They "fixed" the 0W, 5W, and 10W 40 grades to a 3.5HTHS, making them actually reflect that they are a 40.
They subdivided the 20 into some areas of 16, 12, and dropped an 8 into the high temperature classifications.
As to my statement
Quote:
The "grades" that we know and love (well some do, I don't)
If you look at the current chart, you can see that the lighter oils overlap in KV. That's just silly.
The HTHS is the number that is representative of engine protection, as they determined in the 70s and 80s, and the overlap in KVs for the lighter grades reflect the fact that they can have a number of KVs for that protection.
The 50s and 60s share the same 3.7HTHS minimum.
In Shannow's ideal world, the ratings would be changed to
xW - HTHS
