Originally Posted By: used_0il
It's too bad the HTHS is not listed for those
two engine oils.
My guess is that the HTHS of the 5W40 is not
proportionately higher than the 5W30 for the
KV100.
The GrIII 5W40s I've got/had are usually 3.8, the 5W30s usually 3.6, so yep, you are right.
Look at the -30 CCS, and the flashpoints...the 5W40 is (probably) a lighter average basestock than the 5W30...much like the mobil table suggests.
Originally Posted By: used_0il
When SAE introduced the winter "W" designations,
the spacing was equal, moving up every 5C, except
for 20W and 25W, which has an approximate 4C
spacing. But instead, the viscosity allowance
was raised or given more headspace.
(Sorry, I couldn't resist the temptation.)
The SAE grades don't appear to follow an equal
scale of proportionate steps, and instead of
revising the list that would actually mean something,
they now have SAE 16.
Show me C Flat on a piano.
Only semi rational reason I've seen for the grades is this (still trying to find an original J300 to add to my data), but here's the alleged verbage.
http://www.jcmotors.com/images/understanding_motor_oil_viscosity.pdf
The article has holes in it in other areas, that's why I'm chasing old J300s. As an aside, VI was based on their best crude being 100, and worst being 0, clearly what was available at the time, but even the "0" had a viscosity index.
Quote:
To properly answer that question a bit of history is required. Motor oil is like every other fluid in that its viscosity varies with temperature and pressure. Since the temperature and pressure conditions under which most automobile engines operate are reasonably constrained the viscosity requirements for a motor oil can be quantified and standardized. In the United States, the organization that sets the standards for performance of motor oils is the Society of Automotive Engineers (SAE). In 1911 the SAE published the first version of their standard (SAE J300) for motor oil viscosity. The SAE wanted a system that reflected the suitability of an oil for use as an engine lubricant and was easy for the consumer to understand. Their initial specification defined five different numbered grades for motor oil (10, 20, 30, 40, and 50). The grades were based on flow rates measured at 210° F (100° C) as shown in the table to the left. Very shortly the original specification was updated to use a standard scientific unit of viscosity (cSt) instead of time. By 1926 there were six grades of oil defined (SAE 10 through SAE 60) specified by viscosities measured at two temperatures - 130° F (55° C) and 212° F (100°C). Over time further shortcomings in this system were identified and it has been amended numerous times. A major change was made in 1952 when the original set of grade designations was augmented with the addition of a set of winter (“W”) grade designations (10W, 15W, 20W, 25W, 30W) which were specified by viscosity measured at 0° F. This change was instituted to address problems with cold weather oil performance. Engineers and consumers alike had come to realize that the existing grade specification did not adequately describe the cold weather nature of existing motor oils. At freezing temperatures an oil meeting specification SAE 20 refined from aromatic black Gulf crude was much thicker than an SAE 20 refined from light amber Pennsylvania crude. Engineers began to measure this difference in behavior with a viscosity ratio metric called the Viscosity Index (VI). The Gulf crude based oils which had lower indices did not provide the same level of engine protection in winter conditions as Pennsylvania crude based oils which had higher indices. This led to the well deserved reputations for superior cold weather protection of brands such as Pennzoil and Quaker State. Now engine manufacturer’s began to specify “W” grades for winter use.
by assigning 10 second bands back in the day, on kinematic viscosity, they made 20 a ridiculously wide viscosity band, and the others were "narrowed up" due to them being the same band, over a vastly different mean.
Trying to fit the 16s and whatnot in, they've carried on the abomination.
Should be xW-HTHS.