While I wait for the new radiator to arrive it seems like a good time to flush the cooling system.

What is the best way to do the flush with the radiator out of the loop?

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI

What kind of flush? Chemical? Fresh water?

Since chemical flushs (which often cause as many problems as they solve) mainly benefit the radiator, I would just remove the thermostat, insert a garden hose and let the water flow. Remove the block drain point to allow most of the water to escape. Back flush the heater core/plumbing separately.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I was thinking about jamming the garden hose into the upper radiator hose and running it for 30 minutes.

Would remove the lower hose from the radiator?
Open any drains?

__________________
.
1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI

Unless you remove the thermostat (you could reinstall the housing), you won't be flushing anything but the hose.

May as well remove the entire radiator.

Block drain. Right side of engine block. (I would initially flush with the drain plug installed.)

https://www.bing.com/images/search?q=om617+drain+plug+block&FORM=HDRSC2#view=detail&id=B61CDE39E54D21BE2FAEFC1A4A37517D3B70E75D&selectedIndex=0

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Best to flush it with the old radiator in, so it catches all the junk. You need to drive it to get coolant hot. Flush out all coolant (open block drain) and fill w/ pure water, flush again, then add Prestone SuperFlush or such. I use powder citric acid (ebay), which is the same. Then flush again and run a bit with plain water. Finally, when installing the new radiator I add a screen in the upper hose to catch any debris so it doesn't hit the radiator and take it out after a month or so. I buy stainless mesh strainers at the dollar store and cut them. I recently put Evans waterless coolant in both my 300D's (after removing all water), and no problems so far.

I'd think twice about acid flush for fear of creating leaks in the heater core that's not currently there. If you must acid flush, bypass the heater core!

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Isn't it a little late for that? Or did I misunderstand the meaning of "broken radiator neck?"

The cleaning product currently listed on the Prestone website is certainly not the same a citric acid. Prestone Radiator Flush+ Cleaner is non-acidic, according to the description.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.