7.3L Power Stroke Coolant Flush

7.3L Power Stroke Coolant Flush & Cooling System Service Guide

Cooling system neglect can lead to sludge and buildup in the radiator and engine water jackets. Like engine oil, coolant breaks down over time and certain compounds, especially silicates, fall out of suspension and begin to collect. This process not only decreases the thermal efficiency of the cooling system but threatens to clog radiators, oil coolers, heater cores, etc. The only way to avoid such conditions is to flush and service the cooling system routinely as requested in the OEM maintenance schedule.

Ford recommends servicing the cooling system initially at 50,000 miles and at 30,000 mile/36 month intervals thereafter. A basic cooling system service should include a flush (with or without the use of a cleaning solution) and replacement of the upper/lower radiator hoses, radiator cap, and thermostat. Additionally, the cooling system should be thoroughly flushed with a chemical treatment anytime oil or fuel is found mixed with the coolant, such as in instances where an oil cooler or injector cup has failed.

7.3L Power Stroke Coolant Selection

We typically use standard Motorcraft VC-5 ethylene glycol engine coolant in the 7.3L Power Stroke. Converting to an ELC is desirable, but the 7.3L Power Stroke is typically less sensitive to coolant type than engines such as the 6.0L Power Stroke and early IDI motors. If you prefer to upgrade to an ELC (extended life coolant) to reduce future service costs, it is imperative that the cooling system is thoroughly flushed first. While the 7.3L Power Stroke doesn't generally have cavitation issues, we highly recommend adding a SCA/DCA (diesel coolant additive/supplemental coolant additive) to the cooling system if not using a pre-charged ELC. The SCA/DCA level should be checked and adjusted routinely between services.

ELCs are typically found in medium and heavy duty diesel applications. Their service life is typically in the 300,000 to 600,000 mile range, meaning they are more resilient to thermal breakdown and contamination. ELC options that we've used with great success include Shell Rotella ELC, Shell Rotella Ultra ELC, and Fleetguard OAT ELC. International also has their own ELC, but it can be difficult to locate a dealer. If you're going through the trouble of converting to an ELC, select a silicate free coolant.

7.3L Power Stroke Coolant Flush Procedures

The procedures below are being performed on a 1994 - 1997 generation Ford F-Series. While the cooling system is slightly different on later 1999 - 2003 model year engines, the procedures are entirely compatible with all 7.3L Power Stroke diesels.

We tend to recommend avoiding generic over-the-counter flush/cleaning solutions that available at your local auto parts store. The OEM solution is Ford VC-1 Premium Cooling System Flush; it's hard to go wrong with the product developed by Ford for Ford vehicles. Fleetguard Restore (CC2601) also comes highly recommended as it is formulated to remove silicate gel (buildup), oil, and fuel remnants.

The flush/service procedures below are time consuming as they do not require draining the engine block and therefore do not completely drain the system at once. Instead, they simply remove the old coolant by means of a series of distilled water flushes. After enough flush cycles, the amount of old engine coolant remaining in the cooling system will be negligible at best. Plan on purchasing in the ballpark of 20 gallons of distilled water. Tap water should never be used in a cooling system - it contains particulates, minerals, and chemicals that do not belong in with your engine coolant.

Part Numbers for Cooling System Service

Part Description

Part Number


Upper radiator hose

1994.5 - 1997

Motorcraft KM2989

1999 - 2003 single alternator only

1999 - 2003

Motorcraft KM4495

Lower radiator hose


Gates 21405


1995 - 1997

Gates 22216

1999 - 2000

Motorcraft KM4542

2001 (before 4/29/01)

Motorcraft KM4542

2001 (after 4/29/01)

Motorcraft KM4671

2002 - 2003

Motorcraft KM4671


1994.5 - 1995

Ford F4TZ-8575-CB

Thermostats not interchangeable between all model years

1996 -2003

Ford F6TZ-8575-EA

Thermostat housing

1994.5 - 1997

Ford F4TZ-8592-AA

Replace if excessive scale/build up/pitting at mounting flange

1999 - 2003

Ford F81Z-8592-AA

Thermostat housing gasket

1994.5 - 1995

Ford F4TZ-8255-A
Victor Reinz C32036

1996 - 2003 thermostat includes gasket


1996 - 2003

Motorcraft RG602

Radiator overflow/degas bottle cap

Ford 9C3Z-8101-B

Always replace during cooling system service; seal typically hardens, cracks, etc.

Ford ethylene glycol concentrated engine coolant

Motorcraft VC-5 concentrated engine coolant

4 gallons required, procedures below only compatible with concentrated coolant, not premixed Green coolant.

Ford cooling system flush solution

Motorcraft VC-1 Premium Cooling System Flush

"Fast flush" solution

Ford SCA/DCA coolant additive

Motorcraft VC-8 diesel cooling system additive

Optional, recommended w/ Ford coolant


A concentrated engine coolant must be used in order to acquire a proper 50/50 coolant-distilled water ratio. It is impossible to achieve the proper ratio using a premixed engine coolant with these procedures.

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7.3L Power Stroke radiator drain valve location

• The radiator drain valve/petcock is located at the bottom of the radiator on the driver side. Attach a section of 3/8" heater hose or fuel line to the petcock so that it can be drained without running down the radiator crossmember.

• Drain the radiator into a suitable drain pan (minimum 4 gallons).

7.3L Power Stroke coolant reservoir

• Fill the cooling system with distilled water through the coolant overflow reservoir/degas bottle. Fill to the cold fill line, do not overfill the system.

• Start and run the engine, allowing it to reach full operating temperature. You may need to take the truck for a short drive in order to reach operating temp.

• After running engine at operating temp for a minimum 5 minutes, shut off engine and allow to cool. Drain the cooling system once more, then fill with distilled water.

• Once again allow the engine to reach and run at operating temperature for a minimum 5 minutes, then drain the cooling system.

• Add a cleaning/flush solution per the product's instructions. Allow engine to run at operating temperature per product's instructions. Fleetguard Restore requires running the engine for a minimum 60 and maximum 90 minutes at normal operating temperature.

• Drain cooling system once engine has cooled appropriately. Fill system with distilled water. Repeat the drain, fill, run process a minimum 3 more times in order to completely flush any remaining engine coolant and cleaning solution.

• After 3 drain, fill, run cycles, assess the color of the cooling system as it drains. The goal to have a cooling system that is completely filled with clean distilled water and only negligible amounts of engine coolant. If the cooling system does not drain clear, repeat the flush process (refill, run, drain) until the cooling system drains clear. It typically takes us a total of 7 trials from start to finish.

• If the cooling system drains clear, do not refill and continue to service the cooling system. The system will be refilled and balanced with a 50/50 distilled water, engine coolant mixture after the service has been completed.

Coolant reservoir removal

• Remove the coolant overflow reservoir/degas bottle. Clean it with a baking soda solution and let it sit for an hour, periodically shaking the solution in the tank. Next, clean and rinse the tank with dish soap.

• Reinstall the coolant overflow reservoir/degas bottle once all the soap and baking soda has been completely washed out. Install a new cap - do not reuse the old one.

Upper radiator hose

• Remove the upper radiator hose, which connects the inlet at the top of the radiator (driver side) to the thermostat housing outlet (front of engine).

Thermostat housing gasket

• Remove the (3) bolts holding the thermostat housing to the engine block with an 8 mm socket. The rear bolt is difficult to access, but you can remove them all with a 1/4" drive ratchet and a series of extensions.

• Pull the thermostat housing straight up to separate it from the engine block.

• Remove and discard the used thermostat. Note its orientation and install the new thermostat. Clean the engine block mounting surface if necessary.

Cleaing thermostat housing

• The thermostat housing should be cleaned inside and out of any scale, rust, or build up before being reinstalled. In our case, a wire wheel was used to clean the mounting surfaces (hose on one end, flange on the other). We then used a brake cylinder hone to remove the scale and buildup inside the neck of the housing. Remove leftover debris with water and/or a mild solvent like brake cleaner.

7.3L Power Stroke thermostat

• Reinstall the thermostat housing. Silicon is not necessary - if you purchased a Motorcraft thermostat a gasket is incorporated into the outer edge of the thermostat.

• Install the replacement radiator hose.

Lower radiator hose

• Remove the lower radiator hose. It connects the radiator to the water pump. The coolant overflow reservoir/degas bottle also intersects this pipe.

• Install the replacement radiator hose.

Engine coolant, flush solution, and distilled water

• The cooling system capacity on 1994.5 - 1998 F-Series trucks ("OBS") is 7.24 gallons or 29 quarts. The cooling system capacity on 1999 - 2003 F-Series Super Duty trucks is 8.2 gallons or 32.75 quarts.

Note - verify the radiator drain valve is closed before proceeding.

1994.5 - 1998: Add 3.6 gallons (14.5 quarts) of concentrated engine coolant, then fill the system with distilled water until the level reaches the marking on the overflow tank/degas bottle. Add SCA/DCA if desired.

1999 - 2003: Add 4.1 gallons (16.4 quarts) of concentrated engine coolant, then fill the system with distilled water until the level reaches the marking on the overflow tank/degas bottle. Add SCA/DCA if desired.

Reinstall the overflow tank/degas bottle cap and start the engine. After bringing the engine to operating temperature, allow the engine to cool and recheck fluid level. If necessary, add distilled water. Do NOT add coolant, the cooling system has already been filled with the correct amount of concentrated coolant to reach a 50/50 mixture.

Please recycle all used engine coolant responsibly.