WE have the cylinder heads off of our 94 with a 3.8. I think the PO must have put some kind of stop leak in the coolant. The radiator is clogged up and all the hoses have soft chunks of reddish brown material all through them.. Looking down in the engine block coolant passages, there is the same little chunks all down in them and around the cylinder walls (inside the coolant passages)... Also one of the coolant passage holes in cylinder #2 head gasket was plugged up when we took the heads off. I am worried about the holes in the new head gasket getting plugged up with the goop if we put it back together and try to flush the system.

So I was thinking... There are 16 coolant passages in the block deck. Would it be possible to block them off, except one, and use a pressure sprayer to try to back flush some of the goop out through the water pump? Was thinking by leaving the water pump on, we could put the radiator hose on the pump to guide the water into a pan so it would spray all over the place under the hood.

Using a spray wand in one passage at a time a person might be able to use that aluminum tape over the other passages to keep the water from splashing out.
I know that would not flush it all out but it might get good bit of it out. We will be installing a new radiator and heater core and they might get clogged back up too if we don't try to flush out some o the gunk.. . It doesn't look like rust inside the block and it is soft chunks till it gets dry.

What do you guys think?

BTW this is the tool I will use to attempt to flush out the inside of the block with. (unless someone has a better idea). You connect a water hose and air hose so you have the pressure of the water plus what ever the compressor is set at. You could get close to 200 psi. The OD of the tip is about 3/8" so it would fit in the cooling passages. Its a lot like a hand held pressure washer and will blow the paint off of painted surfaces.