Oil weight

I spent an entire day at the last SEMA show, chasing down Triboligists & Chemists from all of the Oil companies I could. Some would tell me more than others. I asked each of them to back up what they could with printed facts.

Mystic, Chevron, Shell & Mobil all said the same thing about Zinc. Any oil that is rated for CD-4 diesel service must contain a minimum 1000 ppm of zinc to meet the spec. Mystic showed me test reports that confirm 1300 ppm zinc in their JT8 oils. Schaeffer documents similar levels on their website. Chevron's master specification book showed 1100 ppm for Delo 400.

STP says that a single can of additive will bring 5 quarts of non zinc oil to 1000 ppm for the batch.

Now, about those pesky viscosity numbers.
Viscosity is actually measured in Centistokes, abbreviated cSt. Oils are tested at 40c & 100c temperatures. No oil gets thicker at higher temperatures.

Let's look at viscosity for several oils @40c first:

5W30 47 -52 cSt
5W40 85 - 89 cSt
15W40 102 - 108 cSt
20W50 129 - 166 cSt
30W 98 - 110 cSt
40W 130-150 cSt

Big differences, and the higher that number the harder your oil pump drive works.

Now, at 100c or operating temperature:

5W30 10 -12 cSt
5W40 13.50 - 15.5 cSt
15W40 14 - 16 cSt
20W50 16.5 - 20 cSt
30W 11.5 - 12.5 cst
40W 14.5 - 15.5 cSt

Obviously, one of them is twice as thick at operating temps than the lowest one, but the gap between a xxW40 and 20W50 is next to nothing at operating temperature.

On an engine that does not require zinc, or with a zinc additive I will run 0W40 Synthetic. No reason not to reduce the load on that pump drive.

Not an opinion, just data.

B.