Relationship between straight weights and multigrades

Interestingly, some common oils are actually marketed as meeting a lower standard than the are capable of with regards to viscosity.

Mobil 1 15W50 definitely pumps well enough in cold weater to be rated about 10W50. (I suspect that since they're marketing it as a replacement for dino 20W50, they thought that it would be more attractive that way.

I've heard, but not bothered to verify that Delvac 1300S 15W40 could be advertised as a 10W40, but since conventional passenger car 10W40's have a bad reputation in the diesel world, it is a marketing move.



There are a variety of methods to increase viscosity at 100c, or decrease it at 0c with additives. In fact I think that it is far to say that different companies take different approaches to hitting the viscosity range they want.


Another thought that is worth mentioning is that a good number of oil companies are actually just blending houses that buy their basestocks and additives from Exxon/Shell/etc. Examples of this would be Amsoil, and Castrol US. It is odd to think that somewhere there in an engineer at Amsoil looking through Exxon's basestock catalog figuring out what additve and basestck strategy to use!

This is interesting. You see, the base oil suppliers release only SAE 10, SAE 30, SAE 40 etc.. as thier finished product. Hence lube manufacturers have no choice but to play around with these viscosities ISO VG 32, 100, 150 cst etc.. and by far 100 cst is the most popular.

Additions of various multigrade packages ensure pumpability at lower temperatures, or make it behave as if it is a free flowing 10w or a 15w oil.

Hussam Adeni

The info regarding the origin of 20w50 oil was on the European Redline Oil web page. I emailed them with my question and got this interesting response:

"So, yes, a 10w40 has got a thicker base oil than a 10w30 - indeed a 0w40 should have a thicker base oil than a 10w30 - and therein lies the next problem faced by an oil purchaser: many high street blenders start with say a 5w20 base stock and then add viscosity modifiers (which thicken the oil at high temperatures) to make 5w30, 5w40 and 5w50 end products. Because the viscosity modifers break down much more quickly than the base stock after a few miles you are driving around with a 20 weight oil in the engine rather than the 50 weight you thought you had! A good reason for using Red Line which uses a minimal amount of viscosity modifiers."

Thats right. Most major oil company's start with a base oil with a lower viscosity index - and VI improvers build it up to a higher range. Hence they break down alot quicklier.

Good oils use better quality base oils (upper type two to higher type three) with higher VI's - and use different polymers to give more lower end range. The end result is that it hangs in better at higher ranges and won't break down as quickly throughout the service life.

Astrixstar,

You are right. Many of the smaller companies to cut costs and adopt this procedure. However bigger brands like Castrol, Shell, Mobil select good high VI base stocks and treat with proven additive packages. Thus products too give good results.

Hussam Adeni

Actually its the bigger companies that generally cut costs - thier R&D spend millions finding ways to balance additive costs/base oil costs. Alot of smaller companies cannot compete on price so they have to compete on quality (unless they're a generic cheapo off the shelf brand). Just by following the guidelines and reccommendations of the additive companies (which develop the API specs) they can manufacture better grade oils.