Originally Posted by mcwilly
Go easy on me, I'm still learning.
Do viscosity improvers really take up that much space? With some comments saying less VI's means more room for real oil. Do we know how much VI's there are in say a 5w20 vs a 0w40 within the same brand? Like 50ml/liter vs 100ml/liter?
The various grades of oil within a brand typically all have the same mileage claims on the bottle. Should a 0wXX oil be run for shorter OCI's because of VI's? Are they really that detrimental to an oils lifespan that an OCI should be cut short or can it comfortably be run for the whole manufacturer's recommended OCI? Is technology improving in this area?
You've got me worried up here in Canada running 0w40's.
0W-40 is not that bad because it uses top-notch GTL/PAO base oils with a very high viscosity index (VI), which helps keep the VII content reasonable, similar to a 5W-30.
The actual VII solid polymer content is around a percent or two. However, it's usually sold as dissolved in some solvent (like a Group I base oil), and the typical treat rate including the solvent can be between about a few percent (for monograde-like grades like 5W-20 and 10W-30) and as much as around 15% (for VII-monster grades like 5W-50 and 10W-60).
Oils with less VII should result in less engine and turbocharger deposits and less sludge. Most use VIIs with good thermal stability though. Some VII types such as PMA require a very high solid-polymer treat rate (several times more than other VII types) but they are rarely used, perhaps a typical application being ultra-high-VI Japanese-OEM oils, as they increase the VI by a great amount.
I have a table that estimates it here. Note that the VII content includes the solvent but it's in arbitrary units and should only be used as a rough estimate to give you an idea. The main goal of the table is to estimate the base-oil viscosity at 150 °C (BO DV150 or HTFSV), which is a more reliable estimate:
https://www.bobistheoilguy.com/foru...erature-full-shear-viscosity#Post5133467