Here is the method suggested by Gooch on another site.
I used the following method and had zero problems.
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Goochs Radiator Flush Procedure
Here's my flush procedure for doing a complete flush:
You'll need the following:
4 gallons of anti-freeze concentrate. In agreement with International who made your engine, I recommend a conventional coolant with SCA, or a pre-charged conventional coolant for the early 99's (pre-2/2/99). For all other 99-up PSD's I recommend a Heavy Duty ELC. But the choice of coolant is yours.
SCA (if using conventional un-charged coolant). Amount depends on the SCA maker (usually 3-4 pints).
Up to 20 gallons of distilled water (you may use less if your tap water quality is excellent requiring less flushing).
A Prestone flush kit with "T".
1-1/2 foot of 5/8" hose (to go on flush "T").
A new thermostat gasket.
Possibly a new thermostat, new coolant filter (if you've added one), or any hoses or hose clamps that you think may need replacing.
Note: A children's small plastic wading pool works good for a catch container. Some fit between the front wheels perfectly.
Flushing procedure:
Park truck on level surface. Allow to cool.
Turn in-cab heater valve all the way to "hot". This will help circulate the old coolant out of the heater core during flushing.
Remove degas bottle cap slowly (be careful if hot).
Drain radiator at pet-**** (bottom left-hand driver's side) into suitable container. Expect at least a 5-gallon bucket-full.
Remove lower radiator hose (at radiator) and drain any sediment and/or coolant from radiator and hose into container.
Remove driver's side block plug with 1/4" socket wrench driver, and drain coolant into suitable container.
Remove passenger's side block plug with 1/4" socket wrench driver, and drain coolant into suitable container (this is best done without an extension on the wrench, working under the truck from the top rear side of starter - no need to remove starter).
Remove thermostat housing and thermostat.
Re-install thermostat housing without thermostat, using old gasket (it's ok if it leaks a little while flushing).
Re-install both block plugs finger-tight.
Re-install lower radiator hose temporarily.
Close radiator pet-****.
Remove heater hose at passenger's side coming off the engine (just below intercooler tube).
Install that heater hose to one end of the flush "T".
Install 1 1/2 foot of 5/8" hose to other end of flush "T".
Install the remaining end of the 5.8" hose to fitting where the original hose was removed from.
*Note*: You could permanently install the flushing "T" in the heater hose if desired.
Install garden hose onto flush "T".
Turn garden hose on until clear water (no green tint) runs (backflushes) out of top of degas bottle. This will take several minutes.
With hose still on, start and run engine for a couple of minutes, again until water coming out of degas bottle is clear (no green tint).
Turn engine off. Turn garden hose off.
Drain radiator at petcock, remove both block plugs, remove lower radiator hose.
Remove flushing "T", the extra 5/8" hose, and reinstall the original heater hose to engine.
Close radiator petcock, reinstall and finger-tighten both block plugs, reinstall lower radiator hose (permanently).
Fill system with distilled water until the degas bottle is full.
Run engine a couple of minutes.
Drain radiator petcock, remove both block plugs.
Close radiator petcock, reinstall and finger-tighten both block plugs.
Again, fill degas bottle with distilled water.
Run engine a couple of minutes.
Drain radiator petcock, remove both block plugs.
Close radiator petcock permanently.
Install both block plugs and tighten permanently.
(You may decide to flush with distilled water one more time if your tap water is extremely bad).
Install thermostat and new thermostat gasket.
Add 4 gallons of anti-freeze concentrate to the degas bottle.
If using SCA, add it to cooling system per SCA manufacturer's instructions (usually 3-4 pints).
Add distilled water to finish filling the system until the degas bottle indicates between min/max.
Replace degas bottle cap.
Rinse off any coolant from engine and underbody of vehicle.
Run engine (or drive truck for faster heating), until thermostat opens and hot air is felt through heater in cab. Periodically check coolant level adding distilled water as necessary. If heater does not get hot (or stay hot), it may be necessary to rev engine or purge air from the cooling system.
Add distilled water until level equalizes (min/max mark) in degas bottle. (this may take several days).
Use test strip to test and add SCA if applicable.
This method will yield approximately a 50/50 mixture of coolant/distilled water. If in cold climates, it is always best to have the freeze protection tested with a quality refractometer.
Write down date and mileage of coolant maintenance for future use.
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Stewart