Overheating & How To Mix Citric Acid Flush

[long-gone]

I just finished the head/top end overhaul of my 1991 300E 2.6.
It started right up and and runs/sounds great. Only thing I did wrong was forget to hook the trans cooling lines back up and pumped about a quart of fluid all over, d'oh!
I still need to flush the cooling system though of all the oily goo left in the nooks and crannies. I put back on all the old hoses and radiator and I'll put the new ones in after I flush it out well and then give it the final fill.
With the thermostat removed, car running and heater on high, it would only take back a gallon and 3/4 of water. I let it run for about 5 min waiting for it take up more water out of the res but it never lowered any more. It wanted to bilge it back out even with the car running. I took it for a short spin and the temp rose to just below the red line. The aux fans kicked in and kept it there till I got it back home (maybe 2 minutes tops). The reservoir was still full. The radiator water tank on the water pump side was steaming hot while the tank on the trans line side was hardly warm. The top hose was very firm, almost hard, with water pressure. I know I'm supposed to bleed the air out of the system with the water jacket plugs on the head and/or the air bleed on the thermostat housing, but I'll have to do that when it's cooled down. Not knowing how to mix the citric acid yet I added a few blobs of shout laundry detergent just as a preliminary cleaner.
I've read as many threads as I can here about flushing the cooling system and different flushes used. I got a bottle of the citric acid powder from the MB dealer but there are no instructions with it. Some of the threads mention
10 or 15% solutions but don't instruct on how to achieve that. Is a 10% solution a tenth of the bottle to a gallon of water?? One thread said you need 2.2 pounds of acid powder to properly flush a system. Is that in 10% increments or all of it mixed with x?x gallons water in one flush?
Also, several posts recommended de-oiling the system prior to flushing. Isn't that what the flushing is supposed to do!? or is there a preliminary "de-oiling" step before flushing. I clicked links supposedly leading to tech articles somewhere her on the subject but they were dead links.
Has anybody here done this and can lend their experience? I'd really appreciate it, Thanks!