I'm replacing my rusty radiator, thermostat, and upper and lower hoses. I also replaced my water pump with the timing belt.

Should I preventatively replace the 27-year-old heater core, or just flush it? It seems to be working, but I'm worried about potential consequences of rusty coolant coming from the core to my radiator. Should I be worried about this?

It's only a $40 part, but I have to remove the dash, which is a massive pain. What would you do?

 

1994 Ranger with 4.0l
Should always includes this with questions

Yes, replace heater core, its easy in a 1994, and they are not expensive, 4 screws in the cab and 2 hose clamps in engine bay
It will have been replaced before

Once it's out of the cab, flip it up side down to let coolant drain out, then shake it, if you can hear coolant still inside or it feels heavier than new heater core(which is super light) then old one has clogged passages, so was on the way out
If it drains completely and is light, like the new one, then save it, for next time, its not original

Just as a heads up, leave one heater hose off the core when refilling the engine coolant, when coolant start to come out the hose AND core, put the hose on, all air is out of the engine
And swap heater hoses around at the core every 2 years, this will back flush the core every 2 years, to keep it cleaner, applies to ALL vehicles, not just Rangers