Stormin Mormon wrote:
I've used a 1300 PSI pressure washer to clean fins. As long as it's
set for fan spray, and the nozzle is a couple inches away, the fins
don't bend. Straight stream bends fins. I must be one of the 0.001%
then?

I once found a trigger spray bottle of "evaporator cleaner" on the
dusty back shelves of some little old hardware store. From the contents
label, it was basically a fairly strong dilution of some acid or other,
I don't remember which. All these warnings about not getting it on
paint, the floor, etc. not inhaling, don't spray yourself in the eye,
etc. Did the job, though.