W123 thermostat replacement - how much coolant?

[D_Ryan]

Good evening all;

Need to replace the thermostat in my '85 300TD (operating temp never gets above 60 degrees).

How much coolant do I need to have on hand to replace what is lost when I pull the hoses / thermostat housing? (Need to lay in supplies, because driving to get it after the fact will not be an option)

Thanks in advance,
Dave