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Flushing the Heater Core

I do not have a shop manual but I think I traced the right hoses. The car heat system should be set to call for max hot air to open the hot water to flow through the core. Your need to tap into the hot water supply hose that runs from the engine thermostat to the heater core. That hose runs across the back of the engine and has a plastic T hose connector in it. I removed the T fitting and used a small hammer head to plug the hose coming from the thermostat preventing loss of the coolant.

Now the other two hoses are the heater core in and out lines. I bought two 3 ft long clear vinyl hoses and two plastic 3/4" hose connectors. At 50 cents a foot I should have bought 4 ft. Next, you want to connect the clear hose extensions with the heater in and out lines. Since the CLR cleaner is a mild acid I used a bucket to catch the outflow and prevent it from getting on the car or my clothes.

Now with the outflow hose in the bucket and the inflow hose in hand I used air pressure to clear the heater core of liquid coolant. If you don't have compressed air, I use lung power. Now I used a funnel pushed into the inlet hose to pour in about 1/2 a bottle of CLR cleaner. Hold the inlet hose up to give some pressure to assist the flow. Just let the cleaner work for 10 minutes or so. I also used a little plus and minus air pressure to slosh the cleaner in and out of the core.

I have an outside the house hot water supply for washing cars in my driveway. I pushed the garden hose nozzle into the inlet hose and turned on the hot water to flow through the heater core. I was happy to see the amount of solid mineral junk that was washed out.

I did this four times. I found that when this mineral buildup breaks free to flow it will cause plugging of the small tubes. When this happens I reversed the flow. Put the garden hose into the core outlet hose. The nice thing about using clear vinyl extension hoses is you can see all the junk flowing out. When the water runs clear coming from the heater core outlet, your done. When you replace the plastic T fitting to put the hoses back together be sure the direction of flow arrow is pointed toward the core. Wash everything down to be sure all the CLR is gone. Tighten the three hose clamps on the T fitting and your done.

If your heater core is not leaking then cleaning the inside tubes can save an expensive trip to the dealer. I hope this can be of help.