I began by changing fuel injectors. Ran into problems, but finally finished it and engine runs again. But before getting back on the road, I found the coolant hose from reservoir to water pump leaking. Figuring I was due for new coolant anyway, I drained radiator, put front end on jack stands to get underneath, and drained block from knock sensor and drain plug. To flush more "dirt," I first poured water into the reservoir, and let it drain out of the block and the radiator. Then I used a 1/4 inch MIP fitting to attach a garden hose to the drain plug opening, then ran a low flow of water in there, and out the KS, radiator drain, and reservoir (never cranked the engine). I removed the MIP fitting, and everything is back together. I am attempting to refill now. Though I started with all liquid drained from radiator, KS and drain plug, less than a gallon of distilled water filled the reservoir. It seems not to be going anywhere. The front end is on jack stands, so it's not sitting level. That caused no problem when the drain plug and knock sensor were removed, but could it be disrupting the bleed system? Will I need to take the throttle body off again and remove the upper hose and thermostat to fill from the top of the block? I hope not. I will be taking it off the jack stands to see if that helps. I am probably making an amateur mistake, but does anyone have any thoughts? I greatly appreciate your expertise. Thank you. Chip

 

What year is the car?? That makes some difference in how the cooling system is filled.

It's best to have the car level when filling the cooling system.

 

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Knowing the year would help, wouldn't it? I'm sorry. It's a stock 1991 L98. I didn't notice the profile page before, but just filled it out. I planned to check for leaks before removing jack stands, but I'm headed out now to lower it . . .
(Later) C4cruiser, you were correct. As soon as I lowered it, the reservoir began draining. I only got about 10 - 11 quarts of water into it, but the angle of the car was the problem. I will run the Prestone flush through it later, and then put in new coolant. Thank you for the help guys. You are the best. Chip

 

Unless the cooling system shows rust or the old coolant was not a nice green, I would avoid the use of chemical flushes. The FSM's for each year all say to flush the system with plain water. It's a PITA but if you would flush the system three times, that will do a pretty good cleaning.

Each flush should be a complete filling of the system, then run the engine until you get to operating temp, then let it cool down and drain. Do it twice more and then add a 50-50 mix of green (ethylene glycol) coolant and distilled water. Also remove the overflow tank in the right side headlamp well and clean it out. Once you have the new coolant in, let the engine cool down and add the coolant mix to the "Cold" line.

Given your mention of a leak, it would also be a good idea to replace the upper and lower radiator hoses. If these are original or even if they are more than 6-7 years old, it's worth doing. Same with the pressure cap.

 

Thanks, C4Cruiser! Doing it right is so much work! When flushing three times, is that draining from the radiator only, or also (ugh) draining from the KS and drain plug too? A lift would be nice to get underneath. My limited tool box and rudimentary knowledge often undermine my confidence, though doing the work (and making mistakes) is the only way to learn.
The lower radiator hose looks like a bear. The FSM doesn't call for it, but it seems removing the throttle body provides better access to the upper hose and thermostat. Would a good mechanic likely remove the TB to replace the thermostat? Sorry for the dumb questions. Thank you for the help, my friend. It is appreciated. Chip

 

The best draining method is to remove the KS as that insures you are getting as much water out of the block as possible. But if the old coolant was in good shape (no indication of rust which would have been some brown coloring), then you may only have to flush twice without removing the KS.

The lower hose is a PITA to remove with the A/C in place. But it can be done with some effort, a few curses that would embarrass a sailor, and maybe tossing a wrench across the garage. Add a bandaid or two and a cold beer and it's doable!

The upper hose should come off without removing the TB. In fact doing that could open up more problems. The t-stat should be removable without messing with the TB. Just be careful around the small vacuum lines coming from the TB and EGR stuff. They are plastic and after 20 years the plastic will have hardened and it's easy to break them. Went thru that with my 87.

If you can see the upper radiator hose clamp, pull it off and then use a razor knife to cut the old hose off. I use some spray silicone when re-installing the hoses. They push on a lot easier that way. Discard the old OEM spring clamps and use new gear drive clamps.