Will 2004 Chevy impala radiator fit 2003 impala?

It may or may not. They are all the same size dimension-ally but are different depending on which code, model, vin, engine size. Best to order what you need, there not all that expensive, otherwise just match it up...look to see if all the hook ups are the same, trany lines, sensor locations, fan mounts etc.

Should fit if the 2004 also had a 3.8 engine

why don't you ck local parts store,if the part#s are the same your in!!!!!!!!!!!!!!!