I am looking at a 04 Lincoln LS with the 4.0 (AJ) engine like my XJ8. Does this engine suffer from any water pump defects, like a plastic impeller? I have looked at many other things in the cooling system and they seem fine.

 

I'm not 100% sure but by 04 I think they had it sorted out. I changed water pump in my 01 LS at 100,000 miles.