quote:I wanted to start a new thread regarding this statement since I think it would be off-topic to talk about it in the Turbocharger failure thread. Anyway, I am a tad confused about how oil companies come up with the viscosity rating that we see on the labels. I think it was MolaKule or someone who told me that ALL multi-vis oils always starts at the high number as the base (ie. 30 weight in a 10W30 rated oil), and then made to flow like a thinner oil at startup (ie. 10W in a 10W30 rated oil). Instead, Bob - with his statement above - says that on some oils this maybe true, but others (such as dino oil) start at the low number specified (ie. it is a 10 weight oil in a 10W30 rated oil), then made to thicken out. Can you guys clear this up for me, once and for all Thanks, Oz
Originally posted by BOBISTHEOILGUY: I think this may be the time to come out and explain something here that is being over looked in this issue and GeorgeCLS or Mola can correct me if I miss the point. So here it is, Newtonian vs Non newtonian fluids. In the case of a mineral oil, you start out with a base oil of 15wt(15w40 for example). You then add some VII to enhance it to the 40wt as it heats up. This is a non newtonian fluid. In the case of a real full synth, You take a 40wt base oil synth. In most cases it has the ability to flow in lower temps to what ever it is tested to.So for example, a company like M1 can make a 40wt synth, test it to the flow propertis of a 15wt and label it, take the same oil, retest it to a 10wt property and label it,again use the same oil and test it to a 5wt and 0wt and relabel those, all being the same oil. This is not a bad thing, but in fact is a win win for everyone as it lowers the cost of production to one oil for many viscosities and also, you could have a 15w oil that actually perform down to a 5wt oil in really sub cold temps if needed. But in all, it's still a straight 40wt with no VII added, therefore it has a natural ability to resist the cold flowing properties. This is a netownian fluid or actually a straight wt oil with the flow properties of some non netonian fluids. Now there is some so called full synth's that need some assistance to get a further spread on the numbers and there is some help added there but in the case of full synths this is the basic premise. Mobil stands out as being one of those from my understanding. Castrol on the other hand would not be.