Originally Posted By: jake88
Originally Posted By: Analyzer
This isn't to condemn those who use 5W20 in their Ford's, Honda's, or any other vehicle for that matter, but ultimately when you factor in fuel dilution, VII shear, or general high OCI wear on ANY oil it will shear down, most used oil analysis show shearing rates of generally one grade, i.e, 40 down to a 30, 30 down to a 20, etc.
The assumption is that the 5W-20 will shear out of grade at the same rate as the 5w30. However, the 5w30 grades have lower initial base oil viscosity and a higher treat rate of polymer thickener. Given the same polymer chemistry, the wider span the multi-grade the faster it will shear out of grade. For the grades under debate, you are talking about 35SSI olefin copolymer.
On the one hand you have VII shear and fuel dilution - on the other hand you have oxidation thickening and evaporative thickening. Those factors are competing, and the influence of one factor over another is dependent on DI package, VII chemistry, driving cycle, engine design, etc.... it is a hodgepodge of competing factors at play. For my drive cycle (1.6L I4) of 40 mile freeway commutes, I am much more worried about oxidation and thickening than I am about fuel dilution.
Hey jake88, just wanted to clarify that I wasn't under the assumption that the 5W-20 & 5w30 would shear at the same rate given similar driving conditions (as you stated correctly the VII added to the base oil between the two are used in different ratios), but that ANY oil under a variety of conditions: fuel dilution, VII shear, high OCI, etc. could experience a drop in oil viscosity no matter what their initial starting weight. You're absolutely right that on the flip side you have oxidation thickening and evaporation losses and are just as important factors as oil shear.
Hey there Clevy! Just wanted to let you know that I wasn't stating that 5W20 are more shear prone than other oils, they tend to be quite stable due to the smaller amount of VII needed, and tons of options for high quality 5W20 in partial and full synthetic varieties available. I'm not exactly sure what in my post is "myth"? My main interest with 5W20 is that Ford and Honda for example recommended the use of 5W20 for many of their vehicles in the US, but in Europe specifically recommended the use of 5W30 for the same vehicles, stating that the use of 5W20 would void factory warranties. This was more visibly seen by European Ford dealerships refusal to use 5W20, and then years down the road team up with Castrol and formulate a new oil spec for 5W20 use (WSS M2C948 B). The only speculation I have concerning this is whether Ford pressured the use of 5W20 to the Euro Ford Branch, possibly explaining their opposition to it for years to come.
