when welding the oil return line, what temperature is the flame? reason I ask is 'cause I have a hand-held micro torch that can flame 1300C, 2500F. is that hot enough or no?

 

I don't think the micro-torch has enough ***** to braze anything, you'll need a good torch for brass. Tin soldering probably won't hold up for long, if at all. I think a radiator shop can take care of that, or a good auto body shop. There are fittings to use that doesn't require any welding or soldering. I think they are called "through-wall" couplers, like a flared or barbed fitting on one end and threaded on the other end with a locking nut......