Oil Viscosity by Brand
 

I went down a rabbit hole and started comparing spec sheets on different diesel oils. Below are the differences in viscosity at 100c and 40c for 5W-30 Synthetic oils.

Will any of these oils (based on viscosity) have a real-world, tangible difference in fuel economy, power, cold start flow, operating temperature protection, etc...? Or are the viscosity specs close-enough that they will all pretty much perform the same?

I've been running Rotella 5W-40 for the past couple of years and decided to give Amsoil 5W-30 a try this year. The engine feels much livelier with the 30 weight than it did with the 40 weight. (used in an '82 240 D24 NA)

Shell Rotella T6 5W-30 Mixed Fleet Synthetic:
12.1 @100
75 @40

Dello 400 XSP 5W-30 Synthetic:
12.1 @100
72.4 @40

Amsoil 5W-30 Synthetic:
12 @100
72.3 @40

Pennzoil 5W-30 Euro L Synthetic:
11.9 @100
71.7 @40

Mobile 1 ESP Synthetic:
12.1 @100
72.8 @40

Castrol Edge 5W-30 Synthetic:
12 @100
70 @40

What does this mean??? (engine feels much livelier)

I used to feel like my car performed better immediately after an oil change. Even with the same brand/viscosity as before. What did I base that on? "Seat of the pants" testing, fueled by creative (wishful?) thinking. :D Did it correlate with actual measurable results? Who knows? Are there ways for us to measure any conceivably tiny improvements?

By "Livelier" I mean that it felt less sluggish from a dead stop. Maybe it's a placebo or the weather.

Anyway, that's going down a different rabbit hole.

I'm just trying to understand the difference in 5W-30 oils available at the moment.

The viscosity numbers all look to be within a similar range to one another.
Are these numbers different enough to make any difference or will they all perform the same in regards to viscosity?