Normally, a diesel purge is using a cleaning agent and running it through your car's fuel system, usually at 100% concentration in a little under-hood "fuel tank" made from a plastic bottle or some such. The one you see most often is Lubro Moly's Diesel Purge. It's supposed to clean up injector nozzles, etc. There are some very good pictures below that paint the picture well:

Diesel Purge Mercedes diesel maintenance tips

An engine flush is using some kind of strong solvent or oil additive right before or at the time of oil change to try and clean the inside of the engine and it's lubrication system. Really the best way to do this is just upping the frequency of your oil changes a few times.

A coolant flush is running some water-soluble cleaning agent and the Mercedes citrus flush and then lots of clean water through your cooling system to remove oils and gunk.

Mercedes Citrus Flush

To the OP:

Are you asking about flushing the crankcase or the water jacket in the engine?

If you are asking about the water jacket there is an FSM procedure for this. You use citric acid powder available from m-b. Also Diesel Giant has a write up on this as well.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Flushing the crankcase.z

Thanks for the input, fellas!

__________________
- 1979 W123 240D 4-speed, 390k miles

Why do you want to flush the engine? Diesels generally don't sludge up as much as a gas engine. Be aware that any sludge that is sitting in crevasses and corners will come loose and likely clog the oil pickup screen. This will lead to loss of oil pressure or if a chunk of carbon gets past the screen a locked oil pump.

Left alone and changing the oil on time or say 1000 miles eariler than normal, any sludge wil stay put and not bother anything or slowly be washed away.

If you really wanted to do something, pull the oil pan and manually clean the pan and pickup as this is where most of the junk will be.

I have a 4B Cummins diesel motor in a Case skid steer that had amber oil in it when I bought it and after 3 full tanks of fuel is still the same color. The injector pump is mechanical not computer.

Stating that something is factually incorrect then offering no reasons why or what is correct carries no weight.