Zinc Rich Oil for Flat Tappet Cams

moper said

I think your premise is correct, but the post is a little misleading. At least to me.
This is how I understand oil ratings:
The numbers that oil is labeled with represent more than one thing, because the oil has to meet required "standards". So it gets confusing. It's like saying it's a certain shade of blue for SAE-API 10W30...lol.
I understand it as the weight of an oil primarily means that it must provide the protection (load carrying ability) of that given rating. The same number includes the viscosity rating, which is about how temperature affects it. Oil thins, or gets less viscous, with heat. Conversely it thickens, or gets more viscous as it cools.
Viscosity number denotes resistance to flow. So the higher the viscosity number, the less easy it flows at a given temperature. A "straight weight" oil may still thin as it heats. But not by much and must always provide the protection that weight oil has to per the SAE-API. I know of no oil that gets thicker as it heats up, and regardless of it's viscosity if an oil carries a certain weight rating it must provide the performance of that rating. So a "0-50" oil has to provide the protection of a 50-weight oil at 212*. Even if it's not very viscous (as in it's very thin). That being said a higher number rating is about performance, not thickness. In mineral-based oils more protection meant it had to be thicker. No so with synthetics. The first time I ran 5-50 synthetic I was terrified because it was so thin compared to the 20-50 I was running. It still had to provide the performance of 50 weight rating, but it was much less viscous. That's what frees up power: less power loss to pump it and less loss as the parts spin through it while maintaining the protection.
The "0*" or "W" number indicates the tendency of that specific oil to thicken in the cold. 30W is thicker at all temperatures than 10W. 10W is thicker than 0W, etc. So 10W-40 is a 40 weight oil which thins less when cold than 15W40 at zero degrees. It still has to protect to a 40 weight rating at 212*. Even though it's technically thinner.

Here is a decent read about it... I still don't think I "get" all of it but I think I get the gist. http://www.pqiamerica.com/apiserviceclass.htm

Click to expand...

I was trying to give a short and sweet answer but as you know its hard to not type a book when trying to explain oil viscosity lol, thats a good article about the general information you need to know on the certification of the oil and how to look and see what specs it meets but lacks a little in explaining multi viscosity oils, you explained it much better than the article did

Heres what i found off of mobile ones site

What is oil viscosity and what impact does this have?
Viscosity is a measure of the resistance of a fluid’s flow. The thicker (high viscosity) of an oil, the slower it will flow.

Most oils on the shelves today are "Multigrades", which simply means that the oil falls into two viscosity grades (i.e. 10W-40 etc). In a 10W-40 for example the 10W bit (W = winter) simply means that the oil must have a certain maximum viscosity or flow at low temperature. The lower the "W" number the better the oil's cold temperature performance.

The 40 in a 10W-40 simply means that the oil must fall within certain viscosity limits at 100°C. This is a fixed limit and all oils that end in 40 must achieve these limits. Once again the lower the number, the thinner the oil: for example, a 30 oil is thinner than a 40 oil at 100°C.

Heres some good graphs that show the viscosity differences

15w-40


10w-40



5w-40



Sae 30



More comparison.

10w-40 vs sae 30

Right off the bat we can see the sae 30 is more dense at all temperatures from 32F degrees to 212F degrees compared to the 10w-40.

But if you look at the viscosity curve the sae 30 curves pretty hard by the time it reaches 32 degrees with a higher viscosity meaning its thicker. The 10w-40 has a less of a curve and remains much thinner at 32F degrees but both are the same viscosity at 212F.

Look at the line from 100 celcius or (212 degrees fahrenheit) to 30 celcius or (85 degrees fahrenheit) in both the 10w-40 and sae 30. From 212F degrees to 85F degrees both the 10w-40 and sae 30 are virtually the same viscosity.
Now look from 30 celcius (85 degrees fahrenheit) to 0 celcius (32 degrees farhenheit) in both the 10w-40 and sae 30, we see that once they both hit 85F degrees the sae 30 rapidly gets thicker all the way down to 32F degrees more so than the 10w-40. Thats why the 10w40 will appear thinner in colder temps, realistically all these weights should appear about the same viscosity when poured at anything above 90F degrees, it seems as though when the temp goes below 85F degrees thats when the winter rating comes into affect as below 30 celcius (85F degrees) the 15w-40 progressively gets thicker more so than the 5w-40 which remains quite a bit thinner down to 32F degrees