Modern Vespa

Mine is air-cooled in the Liberty150i.
Are the ones used in the Vespas, including the 946, water-cooled?

O.S.

No. They are air-cooled as well.

No!

The aircooled 125 or 155cc engines are different to the 125 / 155cc watercooled engines in the GTS! Both are so called "i-get" engines, but aircooled and watercooled engines are totally different.

Aircooled 125/155cc are available in Vespa Smallframe (Primavera/Sprint/946) and Piaggio Liberty

Watercooled 125/155cc are available in Vespa Largeframe (GTS) and Piaggio Medley.

Availability of 125 or 150cc depends on markets / country and local rules regarding to drivers license.

In fairness, my response applied in the US (which is where the OP is based). We do not have the small engine water-cooled Vespa GTS in the US - only the GTS 250/300s and the older GT. Yes, I should have observed that the answer in Europe is a bit different.

So there are watercooled versions of that 3-Valve 155cc engine?
Or is it a different 150?
O.S.

No!

Aircooled 125/155cc = 3v
Watercooled 125/155cc = 4v

In pictures the radiator is the give away. I'm assuming that just won't fit on the small frames?

Right. The radiator in the water-cooled 125/155cc engines sits directly on the water pump (see red GTS) and not as in the 300s behind the glove compartment (see golden Vespa, which makes the construction of the 125/155cc less complex.

Clearly, with the water-cooled engines must go somewhere... whether the water-cooled engine including the required auxiliary units would fit in a smallframe, I have no idea.

Good to know.
So anywhere I read that a Vespa has a "3V" I'll know that is sharing my Liberty 's air-cooled engine.
Strange that they use it in the pricey 946!
O.S.

Performance, everyday utility and balanced price-performance ratio has never been the strength of a 946