Basically there are two ways to clean out an engine, both coolant and oil passages, one method is what I call the 'shock treatment' with 15 min flush for the cooling system and motor flush, kerosene, atf for the engine. I don't like doing it that way. The 15 min coolant flush can leave 'big chunks' the same with the engine flush and those big chunks can block stuff like radiator passages and oil pickups.
The second method is a more gradual method, the 7 hour flush is one where you drain the system, refill with water and put the flush in then drive it for a total period of 7 hours. Does not have to be continous, can be 3 hours one day and 4 hours another but this method breaks the build up down in kind of the reverse order it formed in.
The first time I used it was on an 82 S-10 with a 2.6L v6. It had a side tank type radiator so I could see down one entire side. Did the drain and refill, drove from where I live in the poconos to a service call in syracuse ny, ~4 hours away. Got there and did the service call then headed back home. Took a quick look see before I headed back home and was very happy with the amount of stuff that was gone and the coolant looked almost muddy, but no chunks
. Stopped about halfway home and had dinner, checked it again and I could see shiny solder, got a bit nervous the last hour or so was afraid the stuff was removing it.
At any rate got home, drained and back flushed with one of those prestone back flush kits, changed the tstat, cap and cleaned out the overflow bottle then refilled with 50/50 mix of coolant and distilled water.
One interesting note, a bad grounding system can speed up electrolysis in an automotive radiator which means that the rad and cooling system will plug up that much faster.
In the past every time I used those 15 min miracle flushes I ALWAYS ended up replacing a water pump within a couple of months. The only thing I can attribute that to is the fast flushes break so much crud loose that it acts like an abrasive water blaster and damages that packing.
As far as the engine flushes I feel the same way, those build ups did not form overnite, for long term cleaning I would use either a full synthetic oil like mobil-1 or Castrol or a 50/50 mix, the high detergent properties of the syns will gradually remove the sludge and not do it all at once. All at once could block your oil pickup and for sure will clog that oil filter faster and cause the bypass to kick in which will allow unfiltered oil to circulate. When you do run synthetic oil on a high milage engine you really need to check the dipstick more often, if you cannot read the hash marks on it it is time to change the filter.
JMO
Oh, I also only use Mopar coolant, I have noted that some here have used other brands and have had pump failures fairly quickly. Could be that the Mopar specs are of a slightly higher requirement than 'straight off the shelf at the mart' coolant.