Sudden water loss

Keep a tight eye on it Tommy.
The heater going cold is a sign it’s lost water.
6 litres is almost the entire cooling system capacity so it’s a considerable loss.

Any miss in the engine?
Hard to start?
Smoke?
Above can signal a head gasket problem although the 2.8 was never given to that issue.

It’s hard to detect a leak sometimes without pressurising the system with the proper gear.

Water pump springs to mind, also the heat exchanger behind the oil filter, split hose, expansion bottle cap, split somewhere …. but that’s really more a guess without seeing it although it would be visible if it’s that big a leak.

2 versions Colin.
2.8 idtd was mechanical injectors & pump.... no ECU
2.8 jtd is Common Rail with electronically controlled injectors with high pressure pump, all controlled by an ECU.

Loss of that much water, would normally cause cab heating to go, but followed, very quickly by engine overheating, the run down hill in freezing temperature, could, with all the cold airflow trough the rads, keep the engine from reaching anything like normal running temperatures, for the same reason the temperature sensor in the turbo pipework could have caused the limp mode.
None of that answer's the water loss. I'd get the system pressure tested if at all possible.

No miss in the engine and starts ok Jon

If you were in a steep descent you may have an issue with the pressure cap on the expansion bottle.
It’s designed to vent under excessive pressure and when you descend from height the pressure increases, the rate of pressure increase is 30 M/bar per 1000 feet of fall. If the pressure valve in the cap is weak it could open under the pressure rise causing it to expel the water.

If you’ve drove 200 mile since and it’s been OK (I’m assuming you’re not ascending/descending steep hills in that 200 miles) it would explain it.
I’d call into an auto factor and order a replacement cap and they should have it the next day. I’m also assuming the cap on the expansion bottle is the type with a pipe on the top of it?….. if so then replace it.
If you’re stuck I can have one the same day, in fact I think there is one in the store…. I could mail it out to you.

which moutains Tommy?...there is a full range of dealerships and motor factors in Saint-Gaudens. I used a place called 'Autodistribution' last summer in Saint-Gaudens when copming down from Pyrenees on N125 through Bagneres de Luchon. There is also a Fiat dealership across the frpom from it too.

And cramming in as much ‘wine’ comes next.

I think the wine came first (prioritise, prioritise)…….Maybe that’s why it overheated !!

excellent!...where did you ski?...We are just back from a half term trip in the MOHO to Passo Tonale...great camping aire literally at slope side. Also last year we parked in La PLagne aire with EHU which is again, on the slopes.

Stayed at la Raffort just below Meribel beside the bubble into the village. Meant we had access to the 3 Valleys 600k of skiing. I've skied at La Plagne but never in MH. Whats the Aire like

I havnt had any further bother but changed the cap on the water bottle. I think it was a one off with the cap.