The only way to be sure to not damage the threads on the cooler is to cut the fittings off the cooler lines with a dremel tool.

Cut a perpendicular slot on the nut so you can use a screwdriver to pry the nut open and off the threads.

I cut the lines off and remove the cooler so I can cut the fittings off at my bench.

The first time I replaced cooler lines I tried penetrating oil and heat while being VERY careful, but the threads were still slightly galled. Since then I cut the fittings off, and the threads are always perfect.

__________________
Chad
2013 Jeep Unlimited Rubicon
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL