Have Karcher 5.55J used it twice so far on the bike. Use extreme caution to this day still regret using it, if you like me had the chance to witness the situation of a front wheel bearings full of water of friend no1 and a rear axle full of water too of friend no 2 K bikes then you all stay away from it.
Prefer my hands, the garden hose cautiously, some WD50 and maybe AUTOGLYM products if any available.
My dealer still owes to me an my son the bike wash (dealers offer that every after year service) but we decide to wait for mid March, not so much salt here but still a lot of muck.
Crud and muck are enemies no 1 in northern Euirope and rest assure we will whitneess many more rad incidents this summer, just wait and see (read).
How to clean the rad, to tell you the truth don't really know, I remember a post in old site about proper cleaning but it involved dismantling it and soaking it to some light solution, maybe is necessary for winder daily commuters, but a lot of troubles and worries about proper air vacuum cleaning is involved in such procedure.
Some others stated that ACF50 works, but in any case IMHO pressure washers are not for bikes, bikes are to be treated better than girlfriends.