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One of the most frequently ask questions to our Prestone® technical team is: when and how often should I flush the cooling system in my HD truck? What procedure should I use to perform a cooling system flush on a HD truck?

When To Flush The Cooling System

Whenever there are signs of any contamination in the system. The contamination could be oil, fuel, particulates, or hard water salts leaving deposits on cooling system metals.

If the vehicle has been overheated. An overheated cooling system can breakdown the coolant causing it to turn acidic, which will result in cooling system component failures in a short period of time.

Other reasons to perform a cooling system flush could be mixing of coolant technologies. An example would be if the truck is operating with a HD extended life coolant and someone is topping off with a conventional (green) coolant. This would lower the overall protection and may cause water pump failure or even cavitation pitting of the cylinder liners. If this is occurring, the cooling system would need to be flushed and the system refilled with a HD extended life coolant to get the benefits and extended protection. Flush the system whenever there is a cooling system component failure, remember it failed for a reason.

A regular cooling system maintenance flush should be done whenever it is time to change the coolant out, when the coolant is at the end of recommend mileage or time protection. Refer to the trucks owner’s manual for the recommended coolant change intervals. And last, always remember the saying; when in doubt, flush it out!

When performing a HD cooling system flush always follow the OE Manufacturers flushing procedures. In a HD truck, flushing procedures can be different depending on the year, make, and model. It could be a simple (general) procedure or a complex procedure requiring a scan tool or laptop with the proper software to open and close cooling system valves while flushing.

General Flushing Procedure

Start by completely draining the cooling system, when cold, from the radiator petcock drain. At this time you do not have to worry about the leftover coolant in the engine block, the flush solvent is designed to work with some coolant in the system. Tighten the radiator petcock drain and pour one gallon of Prestone® HD 2in1 Flush and Degreaser into the radiator or reservoir bottle and fill the rest of the system with water. Run the truck with the heater on high heat for 30 to 45 minutes after engine operating temperatures have been reached. Shut off the vehicle and let the cooling system cool down. Open the radiator petcock and remove all engine block drain plugs to completely drain all flush water from the cooling system. You might have to disconnect the heater core inlet and outlet lines to completely drain the flush water from the heat core. At this time flush the system with water letting the water run until water is clear coming out of the radiator drain and engine block drain plug holes. Run water through the heater core lines that was removed, and back flush the heater core running water into the outlet hose until the water is clear and no debris is left. Shut off the water and let the system drain.

Reinstall the engine block drain plugs, reattach the heater hoses and close the petcock on the radiator. Fill the system with distilled or deionized water and run the truck for 10 minutes after it reaches operating temperature. Shut the truck off and let engine cool. Drain the water out of the cooling system again by opening the radiator drain petcock and removing the engine block plugs. Remove a heater core hose to drain the heater core. Reinstall heater hose, engine block drain plugs and tighten the radiator petcock drain. Repeat the last procedure one more time allowing the cooling system to cool before opening the system.

Now it’s time to add the coolant. Make sure all engine block plugs and hoses are reinstalled, and the radiator drain plug is tightened. Check the OEM manual for recommended procedures for filling the cooling system since HD trucks have different procedures depending on year, make and model. Pour in your preferred technology of Prestone Command® HD Antifreeze/Coolant. If using a concentrate pour in half the recommended cooling system amount and top off the rest of the cooling system with distilled or deionized water. DO NOT USE well water or tap water unless you have tested the water with Prestone® Water Analysis Test Strips.

If using a 50/50 pre-mixed coolant and water add to the cooling system until full. Install pressure cap and run the truck to operating temperature and monitor the temperature gauge for any overheating. Let the system cool and check the cooling system level.

Using the Prestone® Refractometer check the coolant freeze point, it should be -340 Fahrenheit. If the cooling system is low and the freeze point has not reached -340 Fahrenheit add enough concentrate to the system to bring the temperature to -340 Fahrenheit, if needed top off the rest of the cooling system with 50/50 pre-mixed to maintain the proper temperature range. If the cooling system is low and the temperature range has a lower freeze point than -340 Fahrenheit add water to the system until it test -340 Fahrenheit. Remember to run the truck to engine operating temperatures after adding coolant or water to mix the newly added fluid to get the correct temperature test reading.

If you’re wondering why remove the engine block plugs during the flush and fill process. This is an important step to remove as much of the contaminated coolant or flush water as possible. If the block drain plugs are not removed 20% to 30% of the contaminated coolant or flush water will remain in the engine block. In a 12 gallons system that equals up to 3 to 4 gallons of contaminated coolant or flush water left in the system. This will contaminate fresh new Prestone Command® HD Antifreeze/Coolant added the cooling system.

Properly dispose used coolant and flush water according to Federal, State, and Local laws.

Prestone® offers three different heavy duty antifreeze/coolant technologies for your HD truck.

  • Prestone Command® HD SCA Pre-Charged Antifreeze/Coolant

  • Prestone Command® HD Extended Life Antifreeze/Coolant

  • Prestone Command® HD Nitrite Free Extended Life Antifreeze/Coolant

Check out all the chemical products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on Prestone® HD 2in1 Cooling System Flush, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

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