I am rebuilding my Renault Twingo 95 and I'm waiting for a new radiator to arrive. In the meantime I was running the engine to move the car to a different location in the yard and to check how it runs. I have a digital temp gauge connected to the body of the water pump. I don't understand why you all say to run it for less than a minute if the operating temperature takes maybe 15 minutes to be reached. Why not just follow the gauge?
Now I attached the serpentine belt to the water pump so I am a little concerned running the pump without coolant in it. I also don't have coolant in the cylinder block.

 

Because without the 'heat sink' effect of the coolant, you will build up a lot of heat in certain areas (head in particular) very quickly.

 

Some cars have gauges that will indicate 0 temperature without coolant. The 944 thermostatic fan switch is in the radiator and will never turn on without coolant. The engine without coolant will have hot spots as it will not have coolant to distribute the heat. You can probably run your engine without coolant for 15 minutes but likely your engine will stall from overheating and you will most likely cook something in your motor.

I lost a cooling hose at the big track at Willow Springs and tried to limp the car back for a mile (less than 1 minute without coolant) at full throttle as other cars were going over 100mph. By the time I got back to the pit, I caused enough engine damage to have warped the block, cracked the cylinder head, collapsed the piston rings (lost compression in all cylinders), and blew the head gasket.

Running it for a minute or 2 from dead cold is probably ok. That's about all I would run it for without coolant.

 

As others have said, running it for a few seconds won't be too bad, but anything beyond that on an engine with an aluminum cylinder head will cause bad things to happen very quickly. BTW, fitting a temp gauge on the water pump when there's no coolant flowing is pointless. Worse yet, fitting a temp gauge anywhere on an engine without coolant is pointless. Under such conditions the temperature at the external surfaces may 'seem ok', inside the engine at the cylinder bores and valve guides the temps will be radically different without coolant to carry that heat away.