Will a radiator from a 2002 explorer fit a 99 mustang

If you can get it mounted, it'll do the job, there's several radiators part numbers associated with the two vehicles in your question so there are variables you're asking us to guess at - V6, V8, 4.0, 4.6, 5.0 motors, and some Explorers have aluminum radiators, plus 2-core vs 3-core radiators. Just compare them side by side to see if hoses and mounting points work. Keep in mind a bigger 3-core radiator will cool much better than your Mustang's stock radiator (assuming that was a steel 2-core), so that may throw off the Mustang's ECU at least until engine hits operating temp. Go to Stangnet.com, there are posts there by members making such swaps. If it worth it? I guess you're saving yourself $100 over the cost of a new stock radiator, so financially probably not worth it, but for performance geeks who made mods to the engine and need a little extra cooling, it's worth it.

No.