I was given a 1998 Jeep Grand Cherokee 4.0 last summer. The previous owner said it always overheated. He parked it and bought a new 4-WD truck.
I drove it home and it did start to over heat. I parked it and started to trouble shoot the problem. I found there was no impeller in the water pump,no T-stat in the housing. I replaced the water pump and T-stat. It ran but would blow steam after a long idle out of the tail pipe. I pulled the head and found the head was completely blocked with Stop Leak material. There was also a 1 1/2" crack between cylinders 1 & 2 exhaust valves.
I just installed a re-built 0630 cylinder head. I flushed out the cooling system and filled with distilled water. The engine runs under full load with AC on at 195-8 degrees F.
Very little heat from the heater core. I can blow through the core it but it takes a lot of effort to do so. Prestone radiator flush did not help at all.
Irontite Thoro-Flush says it will clear any brand of Stop Leak made. It does warn to not run the flush for more than 12 minutes.
Have any of you used this flush and did it work? Was there any damage to the cooling system / heater core?

 

I am not one that favors "repair in a bottle" products. I might suggest that you try to reverse flush just your heater core.

 

I did just that, I flushed the core in both directions at about 15 PSI. I decided not to use the Irontite flush in the event it caused the heater core to fail.