1986 300E overheating
 

The hose that comes from the overflow tank to the tank behind the passenger quarter panel broke, so I replaced the hose. Started the car and it started to overheat again, and there was air escaping from the nipple on top of the radiator. So I replaced the thermostat and all was good, I let the car idel for a good 20 minutes and took it for a drive. This a friends car, so she drove it home and all was good. She called me today and said the car got hot again and air is coming from the nipple on top of the radiator again. What is going on with this car?

Sounds like it needs a new radiator.

And if they keep overheating it, its going to need an engine too.

I found the problem, the radiator hose nipple is cracked. Its the big one top right hand side, can I jb weld it?

Unfortunately repairing is not successful in 90% of cases. You will require a new Behr radiator.
There is a metal collar inside the radiator hose necks. The plastics breaks along the line of the collar. Make sure you refill the system with MB or Zerox G05 coolant

Your never gonna get anything to hold the pressure and temp for that piece Believe me I have tried everything twice. Spend the money on a new radiator as new areas will start to leak even if you get that area patched up as all the plastic is the same and aged the same. Also be careful as the hoses and expansion take will be weak with a new radiator may pop. Mine did so i just replaced them all.