I changed the coolant on my 2011 Twinair last year, and prepared to put 5.3 litres in, as advised.

But the most I squeezed in was, I think 3.5 litres.

The garage had it last week, and they were puzzled that there seemed to be a large discrepancy, too.

Anyway, I've changed it again, and drained it with a vacuum pump, with a tube very low down in the radiator, if not the bottom.

With this appliance of science, it seems that you can only drain around 3.3 litres, or possibly 3.5.

So I've flushed it several times now, till the coolant isn't pink anymore, and it seems that if you want the required 50/50 mix, then you need to assume there's 2 litres of clean water in there, or slightly less. (My science isn't perfect)

I hope this will help someone else in the future, with this Fiat puzzle, on an engine with no available literature.

Cheers.

I got around 4 litres out by having the rear of the car up a touch higher than the front on my stands.

How did you drain the rad?

By taking the bottom elbow off, or the hose off the elbow, or the wee petcock?

Using a pump has been nice and easy, but I'd like to flush the radiator before I refill with coolant.

I took the bottom hose off, my rad didn't have a petcock (blank). I also pumped the bottom hose to get out more coolant.