I also posted on modern Vespa .
My Beverly 350 was same age and colour as yours , This had a leak from that plug near exhaust was very small and sometimes nothing showed , but you could smell burning coolant sometimes .
Anyway I traded it in for another scooter . Last time I checked it has not been taxed or mot tested soon after I got rid . So my guess is it had a massive coolant leak which would kill the engine ?

I would get the dealership to check that plug !

Hi Bingo!

Sorry to hear about your leak. Looks like coolant to me from the photos but could be wrong. I'd be inspecting the easy stuff first starting with tracing the cooling circuit. The water pump is below the exhaust which makes me think the leak is higher up but start there and trace your way along the hoses looking for splits. loose connections etc. When i had mine, i had issues with the factory hose clamps and replaced with jubilee clamps. Its likely that the coolant has been changed as part of the service from the dealer and a hose may not have been tightening up correctly .

I've annotated the photo of your engine bay. the red oval is the feed into the engineblock where the thermostat is.

A number of folks on modern vespa had problems with coolant leaking out freeplugs and i ended up ruining a head gasket but before worrying about that look for the simple stuff first.

BTW the bike looks in great nick!

annotated engine bay

Did you park it on the side stand on return from your last trip?
Ready I ask is I have had similar issue on scooters and was just expansion bottle overflowing at that angle.
Take scoot out locally, warm it up and rule it out.
Good luck, Hatter

Recommended coolant according to the manual is

Ethylene glycol-based antifreeze fluid with organic inhibition additives. Red, ready to use. ASTM D 3306 - ASTM D 4656 - ASTM D 4985 - CUNA NC 956-16

The stuff that is in seems to be pink. Anyone know what I need? I guess I just need a litre for a top up if required?

Here's one example of the right stuff in a 1 litre bottle. Other brands are available.

https://www.eurocarparts.com/p/triple-q ... gKAVPD_BwE

abitmad wrote: Mon May 10, 2021 3:03 pm Here's one example of the right stuff in a 1 litre bottle. Other brands are available.

https://www.eurocarparts.com/p/triple-q ... gKAVPD_BwE

Thanks. I found the 5 litre version of that but I couldnt see the CUNA NC 956-16 bit which I read on Modern Vespa as being important. Am I being too anal about this?

OAT is what Piaggio Vespa use ( From modern Vesap forum,)so the ECP stuff is ok , but buy the concentrate as you are not paying for the added water.

wightegi wrote: Mon May 10, 2021 10:21 pm OAT is what Piaggio Vespa use ( From modern Vesap forum,)so the ECP stuff is ok , but buy the concentrate as you are not paying for the added water.

Any chance you or someone could just give me a link to something ready mixed thats the best stuff to use? you have to remember I am a mechanical numpty.