As I sit here and write this, I just happen to have a bottle of Havoline Extended Life Anti-Freeze/Coolant (DEX-COOL) sitting in front of me. I also have a bottle of the Fleetguard ESXTREME Antifreeze Coolant (Prediluted Engine Coolant, Do not add Water) with a Fleetguard pt. # of CC2785 sitting in front of me. Fleetguard is the prepared one here and is what I am using.
You do not want to mix either of these with the green anit-freeze because they will as mentioned earlier turn to a jello like thickness and once turned - your screwed - heater core and radiator core will have to be removed most likely.
There is a method of flush that works very well when followed and it is cheap.
I am using the Fleetguard 600,000 mile, (5year), 12,000 hour stuff mentioned above.
Drain you radiator and block out. Pull the heater hose from the head and back flush both the heater core and the block till you get fresh clean looking water.
Next take 4 large scoops of electrosol powder dish-washing soap and put it in the radiator as you are running the engine and the water is just warming up. Next step is to go and drive it for 30 to 40 miles and get it good and hot with this fresh water mix and electrosol.
Drain this down and flush as stated before with fresh water. At this point I chose to remove my thermostat and then re-serviced with regular water and took it out again for another 30 miles.
Got back drained down one last time, blew out the heater core with an air hose and serviced up through the thermostat opening and then put in a new thermostat's. The inside of the block and radiator look brand new with no rust at all.
I used the 50/50 mix part # CC2785 through Fleetguard. Was $8. 00 a gallon and I used 6 of them.
I like this stuff better than the factory green and it is approved for this engine. The step of using Electrosol powder dish soap was given to me the the Cummins mechanics who do this on a routine basis. I've got around 23,000 miles of driving on this new stuff and have had no problems what so ever. Good luck on what ever you decide
