Any semi truck shop should have a radiator flush solution, donaldson is just the one we carry, there are plenty of other brands but I recommend staying witha commercial heavy duty brand name like donaldson, fleetrite, fleetguard, or pen cool. Just watch out cause some can be very strong. Meaning that if you leave it sit in the block over night, you wont have a block left. The stronger ones come with a neutralizer to keep it from eating away at the block. If you decide to use soap then first drain the radiator and block. Dump about half a box of cascade in the radiator. Fill it up with water and let it run up to operating temp for about an hour and a half. Drain it out. Then fill with water, run up to operating temp, then dump the water. You may need to do this several times depending how much crap you got in there.

 

Holy crap half a BOX !! I was expecting to hear something like maybe aCUP fullof detergent, not half a box. [:-]

 

Sorry scale that back to a 1/4 of a box. We use half a box at a time in 12-14 gallon systems.