The best XW20 is a mono-grade (!)

[userfriendly]

I don't believe that VI is a driver in the fuel economy game, except during the first few minutes of warm up after a cold start at or near the engine oil's W grade.

If we apply 15W30 logic to PC-11/FA where the HTHS is between 2.9 and 3.2, I see no reason for 5W30 to be the go-to grade except to allow cold starts in winter conditions.
In fact, 2.9-3.0 HTHS is where Duron SAE20 is likely sitting, given the fact it is a high density mono-grade near the top of that grade's KV100C limit.

The problem of an XW20 FA-4 would be maintaining oil pressure high enough to provide enough volume to the piston squirters if the engine was designed for XW30.
Oil pressure in my experience follows bulk oil sump viscosity which reflects KV100C at operating temperature.

 

[SonofJoe]

I know a lot of folks get a bad dose of the wobblies when they see low oil pressure when using thin engine oils but I always see it as a good thing. Oil pressure is like blood pressure. Too high is bad but if it's low, as long as you can still move your fingers, it's okay! My chemically engineering knowledge is virtually non-existant these days but I do sort of remember from my uni days that high differential pressure reflects high energy consumption so getting it down is a good thing.

 

[userfriendly]

The opposite of that would be; High oil pressure cannot be used as evidence of satisfactory lubrication.
Worded another way using extreme cases for proof;
Low pressure with an engine oil that is thicker than necessary all of the time, is better than high pressure with an engine oil that is too thin once.

 

[Garak]

Originally Posted By: SonofJoe
Agreed. Given that for years 15W40 was the go-to oil for trucks, the logical way to get better truck fuel economy was 15W30 (or even 15W20), not 10W30 which seems to be the case. If you don't need the cold-flow performance (which trucks don't because they have lived with 15W40 for decades) why engineer it in?

I would suggest good old marketing inertia as the reason. Yes, 15w-40 was the go-to oil for trucks for years. Back as long as I can remember, though, 10w-30 HDEOs were listed in the manuals for cold weather conditions, and commonly used in this province. So, if a 30 grade with an HTHS of 3.5 or higher turns out to be good enough for year round usage, there is some marketing wisdom to just use the grade that's been produced all along.

As an aside, Imperial Oil had an Esso XD-3 5w-30 up until around CH-4, at least somewhere in that neighbourhood, then it vanished completely when CJ-4 rolled out. Eventually, the Delvac 1 LE 5w-30 CJ-4 E6, E7, E9 came out and has gotten a bit more of a push, lately.

 

[userfriendly]

Esso also had 0W30 Superflow pcmo, (silver bottle with a light blue label) that collected dust on service station shelves.
XD-3 5w30 had 1.49 SA, around 1500 ppm Z and 1350 P, back in the day, they couldn't give the stuff away.

 

[Garak]

I tried to get some of the last of the 5w-30 XD-3, but missed out. Of course, no one wanted it (including me) until it was about to be discontinued, then everyone was in a rush. I had planned on getting a pail or two for the old F-150. Well, the Delvac Elite 222 0w-30 isn't exactly expensive, either.

 

[userfriendly]

I was poking around for a light XW30 synthetic blend that could be used for a base-line FA-4, which must have HTHS between 2.9 and 3.20.
Havoline 10W30 SB; KV40C 64, KV100C 9.9, HTHS about 3.0 to 3.10. The HDEO additive package may fail the 10W CCS as mentioned, but we would be looking at a very good 15W pass.
Using the above model, a 10W20 PCMO could have a KV100C of 9.0 without taking much of a hit on HTHS from a comparable 15W30 FA-4 HDEO.

Edit; The high density of these engine oils combined with good oil pressure would make for very good piston cooling. (!)

 

[userfriendly]

I started this thread before FA-4 and CK-4 was rolled out. xW16s were not yet spec'd in a car, this thread tested the HTHS limits of SAE 16, 20 & 30 using mono-grades for virtual blending. (mixing)
I forgot that 5W16 is not a restricted grade by GF-6 standards.