Coolant capacity Can you tell me the coolant capacity of the Peugeot expert 1.9TD?

Various Coolant Air bleed caps on Peugeot in the link. Of course, you may mean brakes, clutch, steering pump, or fuel. In which case modify the Google search query.

https://www.google.com/search?q=Peugeot+expert+coolant+air+bleeder+location

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https://www.youtube.com/watch?v=lZCEsN5WlJE

Engine completely dry or just a radiator drain?

This information will be contained in the owner manual, which can be downloaded from here:
http://www.repairservicemanuals.com/Peugeot/

On this website you find fuse box diagram and description for Peugeot Expert

Peugeot Expert mk1 1995 2003 fuse box diagram Auto Genius

Peugeot Expert mk1 2004 fuse box diagram Auto Genius

Peugeot Expert mk1 2005 2006 fuse box diagram Auto Genius

dealer can tell you..

I'm not a Peugeot expert, but do you know if the engine is warming up normally ?
The thermostat could be stuck open, or the engine could be low on coolant, or the sending unit for the gauge may have failed. If the engine is warming up you should be able to ground the wire to the sender and watch the gauge move.

Do not add water - use coolant instead. You don't have to take it to garage - see attached picture (point 3) to get to coolant reservoir.

window wipers off remove trim and there is 10 mm nuts, remove them, remove speedo cluster and radio etc, there is 2 10mm bolts below each end in footwells at end bottom of dash, 1 bolt below your ash tray in front of gearstick, u got to get gear stick surround out.

Coolant Capacity, 7.0 Quarts or 6.5 Liters. Make sure you mix it 50% coolant and 50% water, or buy the premixed coolant.