After misfiring for about a week my 2002 Qx4 infiniti engine started overheating. took it to a dealer who changed the radiator then reports that engine needs overhaul after water found now coming from the exhaust. What can I do now . Any diagram to explain this problem?

They changed the radiator and then told you need the engine overhauled? That tells me you don't want to deal with them! Any shop should have tested things out not just arbitraly start replacing parts. So unless your vehicle is still under warranty, then I would take it somewhere else to have them work on it.

Since I am not there to check out your vehicle, this is a WAG on what is going on with your engine.

Since you started off with misfiring - that could be a sign that your spark plugs are being fouled by oil or a few more things. But not usually an indication of a cracked block at least at that point.

But then you add the overheating into the equation - depending on how fast it overheats - right away (a couple of blocks driving) could mean either a blown head gasket or a cracked block but slowly could mean low coolant; radiator blockage, and so many more things.

If your engine was misfiring, you should have gotten an error code from your computer, which if acted on right away could have been a much cheaper fix. Now with what should like either a blown head gasket or maybe even a chrack block you are talking major work and dollars!