I wanted to share a "magical way" I discovered to flush the coolant and get rid of any rust you might have in the system for a 1985 xj6.
(I am new to this so excuse me if I don't use the right names for things, but I will describe them to my best ability)

This is what I did:

1. Opened the expansion tank, removed the plug on the side of the engine block and drained everything that was inside.

2. Put a garden hose inside the expansion tank, controlled the water flow so it overflows the expansion tank a little, and started the engine. (I ran it for about 10 minutes at different RPMs, make sure you don't run out of water in the expansion tank because at higher RPMs the system will spit out more water than it takes in).

3. Close the cylinder block plug, fill the system with distilled water, and drive for about 15 minutes or until the car reaches around 90 C. Wait for it to cool down and drain everything the same way.

4. Disconnected the radiator hose from the bottom of the car that goes down to the horizontal tube, on the left side as you are facing the car. There will be at least about third of a gallon water left. (If you lift the driver side of the vehicle more, more water will come out)

5. Reconnected the radiator hose and with the cylinder block plug out start the car. Watch the temperature, run it only for brief periods so that water inside will evaporate.

6. Closed the cylinder block plug, and slowly filled the system with Metal Rescue. (THIS IS THE MAGIC PART) I bought three gallons Metal Rescue from Home Depot after doing some online searching because my expansion tank was full of rust. I drove the car for a day and a half at least three times a day to keep it warm.

7. I drained the metal rescue and the expansion tank was sparkling! I would expect that the same is going on inside the engine and radiator. I have not encountered any problems so far whatsoever due to the chemical, it is virtually safe for anything except for rust.

8. Filled the system with distilled water again, closed the cylinder block plug, ran it for few minutes and flushed it out again.

9. Disconnected the same radiator hose the same way as described above and drained the remaining water out of the system.

10. Reconnected the hose, closed the drain plug, and slowly filled the system with a Prestone any color coolant. DONE and don't need to replace my expansion tank.

Metal Rescue was about $25 per gallon, but was worth the money. You can re-use it for other things if you would like to collect it when flushing.

Feel free to ask me anything about the process by a private message or add on to the thread.

 

good tips but you forgot to bring the car up to temperature so that the Thermostat is in the open position or hot enough to open easily before you do any of the above.

another option is to remove the Thermostat in advance of flushing the system, but doing that can break the thermostat housing stubs creating a problem.

Did you turn the Heater ON to full heat while doing this? The idea is to flush the Heater Core at the same time.

what is Metal Rescue for? What do the instructions say it does? (the expansion tank being plastic, not metal), I've used Prestone Super Flush in the past, two bottles added to the expansion tank after draining system and refilling with garden hose water.

 

Yes! I brought the car to about 90C before the first flush.

Yes! Forgot to mention. I put it on Max High Heat for Defrost when running the water from garden hose and occasionally turned it on and off while driving when the Metal Rescue was inside.

I found it odd too but it seemed that the rust in the expansion tank had penetrated the inside of the tank. I was thinking about removing it and scrubbing it off, but was worried that if that was happening in the plastic tank what was happening inside the radiator!

Metal Rescue polished the tank so I am sure all other hoses or other metal parts have no rust left on them anywhere.

Here is the youtube video that prompted me to use Metal Rescue:

 

thanks, I got it,

the guy in the video says that he first drained and then ran the engine dry;

then he added Metal Rescue and ran the engine with it inside. How many gallons of Metal Rescue did he put in? did he add water? (the video is not clear on that).

 

I assumed that he did not add any water when I read that Metal Rescue was already a water based solution. The instructions for de-rusting other metal objects did not call for adding water. The instructions said to submerge the objects into the solutions from 2-24 hrs or until rust is removed.

I kept it in the system for about 36 hrs.