Originally Posted By: 67King
I'll be honest, I think a high VI is WAY overstated. I know some people look at that as the single criterion for whether or not they use an oil. When the term was created, it was on a scale of 0-100. Now we have companies claiming VI's of 200?
Why do I not like that as a single criterion? I don't like the trade-offs.
I know Red Line was mentioned, and I'll get back to that. But I've got Mobil 1 0W50 info, as well. And obviously, a 0W50 will have a higher VI than a 0W40, since is it just the KV at 40C versus KV at 100C. The resultant VI is 186.
So, how do they get it so high? Base stocks? Nope. Ester and PAO base stocks peak in the 160's. So to get such a high VI, you absolutely MUST use viscometrics. So what is the big issue with that? Two things. What is the HTHS of 0W50? 3.8. Now let's compare that with the Millers' 10W50. Its VI is "only" 173. But, its HTHS is a minimum 5.1.
Why is that? Because Millers' philosophy is to obtain VI as much as possible through base stocks.
What is another effect? Someone was talking OCI. For Mobil 1 0W50, Mobil 1 claims you may be able to get 500 miles or more out of the oil (
http://www.mobiloil.com/USA-English/MotorOil/Oils/Mobil_1_Racing_Oil_FAQs.aspx#FAQs3)
"What is the drain interval with Mobil 1 Racing 0W-50?
Oil drain intervals in racing conditions can vary widely. Depending on specific racing applications and conditions, intervals of 500 miles or more are attainable."
Why might it only be good for 500 miles? What are the failure modes? Primarily, it will either lose viscosity, or it will become acidic. We know that there are some race oils out there that become acidic. Ca content in those is around 650ppm. But for Mobil 1, it is 2500. That's a pretty robust additive amount to prevent the onset of acidity. So in all likelihood, its failure mode is that the viscosity improvers break down. If you read the link I provided for the Millers, after 1700 race miles, the viscosity was still very robust. Oh, and again, that HTHS thing - the 5W40 is 4.4, which exceeds the HTHS of the Mobil 1 0W50, which is 3.8. Lower weight oil, higher HTHS.
That said, I'm not trying to pick on Mobil 1. It was just an example of the tradeoffs you get when you look only at VI. That may be a worthwhile tradeoff to some people, but in a race application, it is NOT a worthwhile tradeoff to me.
So where does the MObil 1 0W50 outperform the Millers 10W50? Pour point. Cold crank viscosity. But in places where it gets really, really cold, won't you be running a thinner oil, anyway? So there, I'd be wondering again why VI is as important as the pour points, coldcrank viscosity, etc. But as for protection at startup, which is why you are after a low cold viscosity, I'd refer to the above charts. The NT offers a level and type of protection that is unattainable with typical oils. It serves almost as a solid lubricant.
Another thing that comes into play is how well the oil sticks around. A question was asked about CF for Red Line (presumably that is what RL meant). We've measured a few, not all, of our competitors. Red Line is one we've measured. Its CF is about 70% higher than Millers at operating temperature. But what is really scary is how poor the oil film is. You can go here and look at several competitors. Red Line is one of the ones there, I'm not going to label which one. A few competitors fared much better than Red Line.
http://performanceracingoils.com/dynofriction-ezp-9.html
A quick note about these measurements. They were taken on a HFRR machine. THe reason is because the CF referenced here is only for boundary conditions, which the HFRR measures. When you've got an oil film established, the only friction is viscous, meaning that viscosity is really the dominant factor. The oil film measurement is done resistively, from 0 conductance (100% oil film) to 100% conductance (0% oil film).
So where does this come into play with cold start? Again, protection. I do not know for certain why the oil film is so poor. Generally, ester is polar, so it should help. Red Line has tons of ester, too much by some considerations, yet its performance was on par with another colorful competitor who uses zero ester (these are race oils, so it uses a lot of PAO). I believe, though I can't say for certain, that it is because of the ZDDP in Red Line. The ZDDP content in Red Line is about 2200ppm, which is almost twice as high as most race engine builders we've talk to think is ideal. Ester is polar, zinc is polar. They fight each other for surface area. So what I think happens is that the high levels of zinc impede the ester from getting surface area, which is why the film strength is so poor.
So what does this have to do with start up protection? Well, again, I'm stating my theory here, but a healthy film will be indicative of the oil sticking to the metal, and if it sticks better, it will hang around longer, giving you better protection while waiting for the oil to flow through the engine.
Great information, thank you. I also believe Redline has some serious deficiencies.
