internal coolant leakage(long post)

first off this is my nissan's engine, I just thought I ask some of you all first before my nissan site. Heres the deal. 6 mo. ago it began to run hot all of a sudden. I flushed it changed the pump and thermostat. seemed to be a little better, but shortly after... I took it on a trip and on my way back it was running real hot. finally the plastic top of my rad sprung a leak which I repaired and was on my way again, another 20 miles or so the rad neck broke off. ultimately It ran hot and blew gasket. So after towing and a long story, I tore it all down to the block, ordered a rebuilt head,and installed a 2 row all metal Rad.put it all back together and took it for an 8 hour back home trip. no probs, temp never went past half.once home with it and happy it had made the very testing trip,I was satisfied with the repairs I had made. drove it for a couple few weeks. and as the first cooler weather came along it ran hot again all of a sudden. So I immediatley took it to where my mazda was and parked it. drove the mazda till I had a chance to check it out. I started it a couple times after that when I began to notice coolant smoke pouring from the tail pipe.... Again I removed the head and replaced gasket, this time no fix. Although this time the cylinders and combustion chambers of 2 and 3 looked to have gotten hot and had lots of carbon buildup. during the first replacement cylinders looked excellent and head new. Would anyone like to discuss this with me so I might determine what to do next?

just my 2 cents id replace the motor if its like that....

SOUNDS LIKE YOU MIGHT HAVE CRACKED THE BLOCK (COOLANT PASSAGE LEAKING), ESP SINCE YOU PUT A NEW HEAD ON IT, AND GASKET.

That is exactly what I was (assuming). How much should I expect to pay to have the (disassembled) block and head magnafluxed? I think my next step could be a complete tear down inspection.

DON'T KNOW ON THE MAGNAFLUXING, SORRY! CALL SEVERAL REPUTABLE PERFORMANCE SHOPS AND ASK THEM, IF THE BLOCK IS CRACKED YOU WOULD PROBABLY BE BETTER OFF JUST GETTING A REPLACEMENT INSTEAD
OF REBUILDING IT.

Well the way I see it, a rebuilt (stock) longblock may be $1200 to my door, and I'm curious for knowings sake, what has happend to mine, Only 140k mi. which was A ok till the current issues. I can get another block from a yard or Known donor If thats the case. and would like to comepletely (build) my first engine. I have some really good tools,and who don't alway's need more? lol. along with an engine stand. and have been looking for a good cherry picker... as I sold my last one(damn it ).so It's totally possible, and has become quite necessary. The truck runs damn strong as is (i know better than run it) And as good of shape the whole truck is in,I refuse to give it away, personally I'd like to see it lay some drag. YOU know what I mean. Thanks

Did you check the spark plugs?
It will tell you which cylinder is leaking coolant.
Spark plugs will be very clean like freshly steam cleaned if head is leaking.

Presure test the cooling system.
Remove the spark plugs.
Crank the engine and see if any spark plug hole squirts coolant.
Do you have warranty on the head?

I cleaned all the plugs when I replaced the gasket this second time and noticed 2 and 3 were black.All were new 2500 miles ago.I will try the things you mentioned. Yes it is warrented with the exception of overheating. I think there is supposed to be some kind of indicator? dont know if it was triggered. Thanks I'll work on it tomorrow if no rain.

Did you check and retorque the head after the first week?