[Padawan]

From the owners manual. Several grades are good for above 86 degrees (F) - 5W-30 apparently isn't one of them.

It's probably worth noting that the oil charts outside of the US do, in fact, list 0W-30 and 5W-30 as being appropriate for temperatures above 86 degrees.

Evilution has a "rest of world" chart for reference: Evilution - Smart Car Encyclopaedia

 

[Padawan]

The engines for the rest of the world are also built differently. It could even be something as simple as the gearbox being programmed with a bit higher shift points.

Do you have any actual proof of this? I'd be extremely surprised if Mitsubishi were supplying special "US-spec" engines to smart, and even more surprised if Mercedes-Benz used something such as minor shift point variations (which we also have no proof of) as a basis for the oil chart in the US manual.

The more likely scenario is that the chart was intended to more positively portray 0W-40 as opposed to the more commonly-available 0W-30 or 5W-30 for use in all US climates (of which Mobil 1's 0W-40 is the most readily available "MB-approved" variant here in the US).

 

[Padawan]

At least older US-spec smarts were 10:1 compression ratio, while the N/A smarts for the rest of the world were 11.4:1.

Some of the earlier documentation stated that they were 10.0:1, but I have yet to see anyone present actual evidence (different part numbers across the model years for pistons, rods, etc.) to indicate that this discrepancy was anything other than an erroneous figure in the manual.

Even if the earlier US-spec cars were in fact delivered with a lower compression ratio, the change would not necessitate a different oil specification from that of the ROW cars running a higher compression ratio. And as the higher compression ratio began being listed in the literature at least as early as 2011, it would certainly offer ample time to "update" the oil chart accordingly to ROW-specs if that were indeed the reason for the original modification to the 30 weight values.

 

[Padawan]

Now I am getting even more confused (between jwights chart & evolutions chart)

The chart on Evilution's site is the one smart has provided outside of the US for a number of years.

If you have difficulty accepting that Mitsubishi somehow re-worked the 3B21 exclusively for the US market in such a way as to require different lubrication than the engine it provides to smart for the rest of the world, then the Evilution chart is fine.

You might also be interested in learning that it had previously been determined that Mitsubishi delivers the engines to smart filled with a non-synthetic oil (most likely 5W-30).