1.blocked rad (4 blocked elements is enough to cause overheating)
2.coolant leaks (pipes clamps,broken hoses,needle size punctures,matrix o rings,matrix)
3.blocked hoses (only way to test is remove/replace)
4.water pump (leaking from "eye".noisy bearing,bearing play,no water coming back 2 exp)
5.viscous fan clutch (not engaging,slow fan turning.rolled newspaper against fan blades 2 test,if it can be stopped=it is faulty)
6.tstat (cold bottom rad hose=stuck closed,temp needle playing=stuck open)
7.serpentine belt (cracks,dry,slipping=faulty)
8.dirty condenser, (if u have a/c) (prevents air circulation)
9.expansion cap faulty=coolant going out,air staying in (valve stuck open or close)
10. airlock (all mentioned above)
these include water and air circulations,these things must be CAREFULY CHECKED.it is ur checklist,the first thing to do BEFORE looking for hg failure,porous block,slipped liners.
as for ironite,it is ur choice,but in my humble opinion it must be used ONLY when all of the above was checked,replaced,done !!! and no money for new block !!!...
and it is a temporary fix as most of the well reputated/experienced members have told u.
it is ur choice to take it to a garage to diagnose or rodd ur rad...! Most of the gentlemen here will explain and inlighten u and share their experiences.the choice is urs...
good luck