Vehicle: 87 300TD

What is the difference between water pumps with cast iron impellers versus composite impellers?

Since my radiator decided it did not want to retain coolant anymore, I'm replacing it and some other cooling system components. Water pump, thermostat and lower hose are also on the list due to not knowing their history.

Are there any other things I should inspect or replace while I've got the cooling system open?

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87 300D. Thanks DieselPaul
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