I'm going to drain and flush out the cooling system in a 1985 m/t 22re using distilled water. After the final drain of the radiator and engine block, how much water is left in the system? I have heard that there is always a little bit trapped in the system (would that be in the heater core?) after draining and I'm wondering how much exactly so I can add the right amount of concentrate. My shop manual only gives the total capacity of the full system, not what is leftover after draining.

 

There's a lot of little nooks and crannies that hold a little water. Presuming that you're working on level ground, as you should, if possible, the best way *I've* found is to open the heater valve all the way, the drain cock on the radiator, the drain cock on the engine block, and, once they get done dribbling, pull the bottom radiator hose off. You WILL get some water out of it. The first time I did it, since I was going to replace all 3 radiator hoses when I drained and flushed my system, I got a nice cool shower from the hose. Right in the face.
This was in Yuma, Az., so the water actually felt pretty nice, working outside in 110°F, but coolant in the mouth and eye (yeah, I only have one left) is most unpleasant.
As far as I know, anyway, that's the best way to get the maximum amount of water out.

Once you've done all that, and closed the system back down to where just the radiator cap opening is all that's left, park it on a hill, nose high, or put the front wheels up on ramps. Ensure the heater valve is still full open, to allow the water to fill the entire system properly. Make the radiator filler neck the highest point in the system. When you go to fill it, it's a pretty safe presumption there's no significant amount of water left in it. Fill it with your usual mix, whether 50/50, 60/40, or whatever.
You will NOT be able to put as much mix in as the book calls out. There is always some air left in all those little nooks and crannies I mentioned. That's why you park it so that the radiator filler neck is the highest point in the system. The first time you start the engine, you will get a lot of air out. Not instantly though. Make sure the radiator is full, and just set the cap on with only the first part of it's locking turn engaged. Not all the way tight. You want it to allow water to flow out freely, but not all over the place. You want the water that comes out to go to the recovery tank, which should have been filled with the normal mix to the "FULL" line marked on it.

Let the truck warm up all the way. I'm talking 20-30 minutes. It won't hurt to run the engine RPMs up some ocaisionally. Once the 20-30 minutes are done, tighten down the radiator cap. BEWARE: It will be HOT. Use heavy gloves! Let the engine cool down ALL THE WAY. We're talking first thing in the morning cool. A couple hours, minimum.
Open the radiator cap, and top the radiator up, and do the same for the recovery tank. Don't be surprized if the recovery tank is empty. Not at all unusual. When the air comes out of the system, it should bubble out into the recovery tank, and then overboard, and, as it cools, the radiator will draw water in from the recovery tank to replace it.Once it's all topped up properly, feel free to drive it.
Don't be alarmed if it pulls fluid out of the recovery tank for a few days, maybe a couple of weeks. It's just bubbling all the trapped air out, and replacing it with water from the recovery tank. You also want to pull the radiator cap before you start it when it's cooled down, and ensure the radiator is staying topped up. If you don't want to open the system by pulling the radiator cap off, another way is to give the top radiator hose a squeeze. If it is easy to squeeze down flat, or you hear water sloshing when you do this, it's a good bet you need to add water to the radiator. Another thing to help make sure it's full is to bounce the truck side-side. I'm fat enough now I can just bounce on a fender or in the door to do this. You may well just get some of the air trapped in the top tank of the radiator out this way.

All this is called "burping" the system, and is an important part of draining, flushing, and filling the system. Any time you drain even part of the water out, like to change the thermostat, you should burp the system.

Does this help at all?
Pat☺

 

Great info, thanks Pat!

 

Glad I could help

Just a small note I forgot. If you do drain some out, like to change the thermostat or whatever, and you want to put it back in, stretch a nylon stocking over the funnel you use. It will filter out even very small particles, without restricting the flow TOO much. Quick, cheap, easy filter you can use.

Just wanted to throw that tid-bit out there.
Good luck!
Pat☺