My experience says that there will be some grease in the system before you start your cleaning. I know a guy who tried to remove the grease by adding a fist full of laundry powder to the radiator. Unsurprisingly, it foamed into a thick, creamy substance quite quickly and the temperature rose. Bubbles don't cool an engine. As a result of his experience, I thought about that for a while trying to find a detergent that will cut grease, yet NOT foam. I settled on couple of dish washer tablets. I put them in and drove about 100 miles and by the time I got back home, the car was still running at the same temperature it was when I set out or a little cooler and the top tank looked a lot cleaner through the filler cap. The grease must be gone before vinegar is added or the vinegar will not get at the rust. I drained the system and flushed it a couple of times and only then, did I add the vinegar. I left that in there for a couple of months, running the engine every couple of days if I wasn't driving the car anyway to keep it circulating. I may have left it there longer than the optimal time because when I drained it, the water was VERY rusty coloured. I flushed it and the next lot of water was not much clearer. That convinced me that the job was not finished so I added vinegar again and repeated the process. I did that (I think) 3 or 4 times till I saw any real improvement.
Would I use that process again? Probably not but it did work.
My Brother in Law used this process and raves about it. The kit comes with enough chemical to do 2 Model A systems so if you have a friend with a similar problem, you might share a kit. There is a warning with that - FOLLOW THE DIRECTIONS. I have no interest in this company and note the prices are in Australian dollars, not $US. Every $US100 will but you about $A150.
https://liquidintelligence.com.au/pr...c-rust-remover