I'm replacing the radiator on the '90 560SEL (yep - broke at the neck).

Any learned opinions on whether to do the acid flush A) with the old radiator on then replace or B) flush with new one in place?

I'm thinking B) - no sense loosening up whatever is in the old one...

Kevin

__________________
"Dangerous with a wrench...and not smart enough to know it"

Stable (in order of acqusition):
'84 500SL, 280SEL (Euros)
'77 280SE. '90 560SEL
'79 450SEL 6.9,
'95 C280 (totalled by daughter 8/07)
'81 280SL (rescued) '88 300CE
'86 560SEC '95 C36
'01 CL55

DD's: '04 S500 4Matic (SWMBO)
'04 F150 Crew

You should flush it BEFORE you replace it....so nothing you lossen can block the new one.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I'm not a fan of the flushing products. I have seen them cause more problems than they solve.

I simply drain the antifreeze, flush with water until it is clear and then put in new anti freeze. I do this every 12 to 18 months.

Good luck,

Something I found awhile ago, but have not seen mentioned on the board. Fresh coolant has rust inhibitors and and other additives to make components last longer. We all know that over time, all coolants lose the effectiveness of those additives and should be changed. Anyone who's ever taken apart an engine or cooling system component will find metal surfaces discolored - generally a tint of the shade of the coolant used. The tint is due to leaching of the rust inhibitors into the metal. That's a good thing. When a component is replaced, that new component will rapidly absorb some of the inhibitors carried by the coolant. If you have 'old' coolant, it could effectively reduce the inhibitors to a level that does not give adequate protection. Therefore, it is recommended that with any component replacement (pump, head rebuild, radiator, etc) new coolant should be used. YMMV