How to Backflush the Heater Core in a Ford F150

The heater core in the Ford F150 is essentially a tiny radiator, located behind the glove box. However, while the purpose of the radiator is to remove heat from engine coolant, the heater core supplies the heat for the F150’s environmental control system. Just as with the radiator, the heater core is susceptible to blockage and should be flushed with the cooling system at recommended service intervals. In the event the heater core needs to be flushed separately, you can generally perform the service yourself.

Things You'll Need:

• Large catch pan
• Hose cutter
• Flush tee kit
• Socket set
• Garden hose
• 1 Gallon coolant
• 1 Gallon distilled water

1. Make sure the engine is cold

Make sure the engine is cold. Place the large catch pan below the heater return hose and then cut the hose in two at approximately the middle point. You can locate the hose by looking under the hood near the passenger side and finding two hoses running out of the firewall towards the engine. The return hose is on the inboard side.

2. Slide the flush tee into the two exposed ends of the heater return hose

Slide the flush tee into the two exposed ends of the heater return hose, bridging the gap created in step one and tighten down the hose clamps with the socket set to hold the tee in place. Refer to the flush tee kit’s specific directions for further details and a diagram.

3. Remove the cap from the flush tee and attach the garden hose

Remove the cap from the flush tee and attach the garden hose to the tee via the adapter as instructed in the flush tee kit’s directions. Once the hose is attached, slide the large catch pan under the bottom of the radiator, remove the radiator cap and use the socket set to remove the clamp holding the bottom radiator hose to the radiator. Slide the hose off the radiator outlet and position the hose so the coolant will pour into the catch pan.

4. Turn the water on so that it flows through the hose and into the flush tee

Turn the water on so that it flows through the hose and into the flush tee. Let it flow until you see clear water coming out of the bottom radiator hose.

5. Reattach the bottom radiator hose by sliding it back onto the radiator outlet

Reattach the bottom radiator hose by sliding it back onto the radiator outlet and tightening the clamp back down with the socket set.

6. Disconnect the garden hose from the flush tee

Disconnect the garden hose from the flush tee and put the cap on the tee.

7. Remove the radiator cap and fill the radiator with equal parts coolant and distilled water

Remove the radiator cap and fill the radiator with equal parts coolant and distilled water. Refer to your F150’s specific owner’s manual for coolant type. After filling, run the engine for two minutes, then shut it off and top the coolant as necessary with mixture of equal parts coolant and distilled water.

Tips

Disposing of any vehicular fluid by pouring it on the ground or into a sewer is illegal and extremely hazardous to the environment. Before performing a cooling system service of any kind, locate a local company that will properly dispose of the coolant after the service is completed.

Video showing how to do a heater core flush on a Ford Expedition:

Helpful comments on this video:

• I have a similar problem in my 2000 F-150 (5.4L Triton V8), although, the issue with mine is a small leak in the head gasket that is forcing gas fumes into the coolant system. I had a flush Spring of last year and it’s worked well until recently. I don’t have the money to replace the head gaskets at this time, so I’m going to attempt to flush the core myself and install a purging valve on the core supply line. Just FYI I would apply silicone grease to those O rings before reinstalling them. It will ensure a proper seal when re-seating the connectors. Does anyone know what size these circ lines are? They look like 3/4” id. I’m hoping it will seat nicely over a 3/4” od copper pipe or perhaps pex for the purge assembly. Just FYI if you do decide to install a purge system, make sure it is not placed directly over the coils. You will end up with misfires if any liquid lands on top of those things. It inevitably will find its way between the coil and plug, causing a short in the ignition.
• I found that if you can connect to the hose so it doesn't leak, then turn the water on and kink the hose, then let the water surge through the heater core. You will break much more of the crap loose. I had a water pump with no fins left. Those pieces of fins went somewhere!