How to Backflush the Heater Core in a Ford F150

by Allen Moore
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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.

Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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.

Step 5

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

Step 6

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

Step 7

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.

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