Engine running hot

Okay, I will check for hot spots and do a radiator pressure check tomorrow because I get off late. I do not know if this has anything to do but I started? Noticing an exhaust leak prior to this problem. I pulled the exhaust cover off and noticed that two nuts were loose, one nut was missing and one bolt or stud was gone altogether on the front corner of the exhaust manifold. I tightened one of the loose nuts and the other one broke off when I tried to tightened it. I went to the parts store and got a bolt for the missing one and a nut for the other one. The bolt was two inch long, only one I could find with same thread. Could it be that the bolt was a little to long when I screwed? Into the head to tighten the exhaust back up? About a week after I noticed it started to run hot. If it is a head gasket I need to know what caused it blow before replacing it.

I stopped by advance auto yesterday about four miles from my job, brought a new radiator cap added more fluid open bleeder to get air out, locked it back down, topped off the fluid and installed the new cap. I drove the truck home about twenty more miles, the truck ran at normal operating temperature all the way home. I thought the cap did the trick, wrong! The next morning before I let for work I checked the coolant, coolant level okay. Started to work, about five miles temperature gauge reading almost hot again! Also, my overflow reservoir is still full during this whole process. Made it work, open the hood and the coolant in the reservoir just bubbling, not overflowing. Two hours later, I open the radiator cap and could not see any coolant in the top of the radiator. After work, I filled it up again before I left and bled it again. I put about a half a gallon of water in this time until I find the problem. Antifreeze getting expensive! Anyway, drove home the ran at normal operating temperature with no problems, twenty five miles. Checked the radiator for cold spots when I got home, cap was cool to the touch, top part of radiator hot, fins hot at the top, middle not to hot, and bottom was kind of lukewarm on the inside, but the engine did not run hot that time after I put more coolant or water it. Do I need to check the radiator when it running hot also? Sorry for writing a book but just trying give you as much information as I can to help with the diagnosis. Mind you, I am not seeing any coolant leaking on the pavement, concrete nor on the engine. What is up? Thanks

Okay, if that's the case, then what is the root cause of the blown gasket. Do not want to just replace the gasket and not know what caused it. Considering it never ran hot before! Do not want to repair twice for the same issue.