I read in my manual about formaldehyde & muriatic acid mix with water to cut crud & scale out of system. Put in & run for a while. Well that's kinda not easy to get today's age....muriatic acid can be, I got that...IIRC it's about 20-30% or so, but....

Seems I also read somewhere, in a manual or on one of the boards about some other mixtures using Kerosene & some other stuff....soda??
I'd think the kerosene or diesel, if used, would need to be really flushed afterwards.
Anyway, I need to do some flushing & cleaning.
Anybody got any good tips?

As a tidbit, several year ago a close friend on mine told about running a Cat for someone. They got oil or something in system from cooler, and decided to flush the system after repairs. Told Don "just run to town & get 4-5 bottles of Palmolive liquid dishwash soap....that'll cut anything!!" So they did. Don told me they puffed & blew bubbles for a month....flushed & flushed....& still blew bubbles all over that hillside! Had frothy stuff all over everything.
I think even today he'd still shoot his wife if she brought Palmolive in the house!!!!

Forget all those "home brew" remedies and get the cooling system cleaner/flush from Cat.
If you need something more aggressive than that get a hold of a local rep for industrial cooling systems water treatment (cooling towers, heat exchangers, etc) they have some excellent descaling products. The best way to utilize them is to rig up an independent pump circulating system where you can filter out the crud and control the concentration levels.

I don't have a home remedy for the scale other than remove the radiator and take it to a reputable shop for cleaning. But for the oil problem we use Cascade for oil in the cooling system on a regular basis. We use the stuff for automatic dishwashers due to it don't foam up. Depending on how much oil is in the cooling system we will fill the system with water and add one container of cascade and runt the machine for a shift. Then let the machine cool enough to get the cap off and pump a little fresh water in to flood the oil off the top before you drain. This makes a little bit of a mess but you don't spread all of the oil back down through the radiator. keep doing this over a couple or 3 shifts and it will come clean and smell nice as well.

Long days! Thanks for the responses.
My curiosity perks up big time when I run up on some of the "older home brew" tidbits of info on various things. I guess I've always been too curious for my own good. When I run onto these various things, even if I never use them, I still start saving away in my "memory banks" for later dates, or sometimes they make other things fall into place & understandable.

I'll probably flush that thing out with clear water 1-2 times starting tomorrow. If I don't feel good about it after that I'll probably go to Cat & get their flush. Actually, Cat flush might be good idea anyway because I have no idea what the PO did or has done. I been slowly getting things serviced & changed out since I got this thing.

Mostly, when I drained it, other than quite a bit of stuck rusty scale inside, things didn't look too nasty till coolant got really low.....always seem that the nasty come out last.