all of them are loaded with VII. they shear to a light 50 fast.

most 10w40s in the uk and europe are good oils, they are forced to be. american 10w40s are some of the worst oils you can possibly buy in the developed world.

Mobil 1 High Mileage 10W40 is an exception, it’s ACEA A3. the problem is it’s priced exactly the same as their 0W40 and many other A3/B4 offerings from Shell and BP.

 

Castrol Edge 0w40 is API SN/CF, ACEA A3, ACEA B3, ACEA B4, A3/B4 certified

….and down the rabbit hole we go!

 

Well, I just changed the oil in my 1997 X330 (XJ6L) with Valvoline 5w-40 Pure Synthetic Engine Oil. I'm going to change it every 6,000 miles as directed.

 

I very much doubt you will have any cause to regret this approach

 

Well not quite the second number after the W or the 60 is the viscosity at operating temp or 100C. So that means that a 60 weight oil will be a bit thicker than 40 when the engine is warm. Or more precisely comparing Castrol 5w40 vs 10w60 the difference of kinematic viscosity at 100C is more than 60%

Sources:

https://www.ftfarfan.com/wp-content/...-40-US-TDS.pdf

https://msdspds.castrol.com/bpglis/FusionPDS.nsf/Files/85D76F35F027EAE080257F72003E3AF8/$File/BPXE-A84TF9.pdf

 

Thinking of trying out Mobil1 FS X1 5W50 on my 1995 X300 Sovereign 4.0 with 250 000 km. Anyone here used this oil?

 

I’m sure your engine would be fine with it.

 

I am guessing (well not really guessing) that Xalty is pointing out that most of the wide range oils (eg 10-60) are loaded with viscosity index improvers (VII) or viscosity modifiers (VMs) that will lose some of their properties (vii´s tend to be polymers that shear in use iirc) at higher temps and then the "hot end" viscosity will drop to lower level. eg from 60 "weight" to 50 or 40 "weight"

Here is a link for deeper in the rabbit hole Viscosity Modifiers II @ Bob is the oil guy forum

 

The viscosity holds up just fine.

https://www.m3post.com/forums/showthread.php?t=1504102