Making coolant swap easy OM603
 

Here's my plan, draining the radiator gets out approx 7 quarts. Refill with 7 qts distilled water, drive with heater on, drain, repeat twice. Then measure in 5 qts of concentrate and top off with distilled water. The cost of distilled water is cheap and our local water is high in mineral content so I'd rather not use it. After a triple rinse I think the system would be pretty clean of the old coolant. This makes the job simple and clean.
What do you all think?

Or just do it the easy way and open the block drain.

It is a fitting on the right side of the block. It has a hose barb on it so you can slip a piece of hose on it to direct the outflow into a bucket.

Distilled water is always better. But, I would first back-flush thoroughly w/ tap water via garden hose, then run on water & citric acid for a day, drain and flush many times, last w/ block drain pulled, then start flushing thru distilled water, then add coolant. In my OM617 engines, after above, I purged all water then filled w/ Evans Waterless Coolant so no more corrosion worries. But, if you change coolant as recommended and use the engine regularly (to circulate anti-rust), corrosion can be managed.

Well I did it
 

On Jay Bob's recommendation I crawled under there and put a hose on it and opened the block drain. The hose barb actually turns with the nut and since I had a rather stiff hose that was curled a bit I was trying to keep it on there and rotate it as I loosened the fitting. Finally I opened the fitting and at that moment the hose fell off and coolant came spewing out. I had to get my head out of the way quick, and when I did I could no longer see the fitting. I struggled to put the hose back on to no avail, and the remaining coolant went down my arm, into my shirt, into my hair and all over the driveway. The only place it didn't go was into the drain pan.

So after that I refilled with distilled again and drove it, so I still got my triple flush. The final drain came out clear so I put the 5 qts of concentrate in and topped off with distilled water. Drove it hard with the heater on, let it cool and topped off again, about 4 oz.

So I won't really say the drain plug was easy, and I won't say it was clean, or quicker. It did get more of the old stuff out though.

I will try a citric acid flush later, not sure how much I want to spend on the car at this point. I noticed a very light film of what appeared to be soot that came off when I rubbed my finger inside the coolant reservoir, and the last Blackstone revealed my potassium to be at 22ppm with the average for the OM603 at 11ppm. With my #14 head I am mildly concerned so I need to monitor this before spending the time and money I had planned for this car.

The drain plug is messy no matter what honestly, it's the worst part of the job, but it does speed things up.

Beware that the citric acid treatment will kill the silica pack in your coolant tank, so you either need to swap in an old tank for the treatment, or be ready with a new tank after the treatment.

block drain makes flushing these a breeze.

buy some heater hose from the autoparts store and the flusher T kit, assemble the kit and open both drains.

Get a bucket and a threaded pipe fitting, drill a hole in the bucket, thread the fitting, install a hose with pinch. Fill bucket with 5 gallons RO water, put bucket on ladder or elevated surface. let it flow through the engine and radiator, it will literally flush out everything with distilled.

once done, reinstall your old heater hose, close drains. fill neat coolant from top hose of engine, reinstall hose. fill up water into exp tank, start engine and burp the air out.

Cool idea except I would add one clarification. Don't permanently install the T fitting in the factory heater hose, as they can leak. Buy some generic heater hose, and build a substitute heater hose with the flushing fitting installed. Only install this hose when you flush and then put the factory (unmodified) hose back in when you are done flushing (and before your final filling).

And if you don't have access to a RO filter, distilled is usually 99 cents a gallon at the grocery store...