How to Check a Heater Core for Clogging

A clogged heater core can reduce or eliminate the delivery of warm air to the passenger compartment of a vehicle. Lack of circulation through the core may also contribute to the buildup of corrosion in the remainder of the cooling system. The simple process you need to employ to diagnose the problem could actually clear the obstruction from the heater core.

Screwdrivers
Pliers
Garden hose with spray nozzle

Instructions

- 1
  Open the hood and locate the heater hoses while the engine is cold. Trace the hoses toward the rear of the engine firewall where they attach to the core inlet and outlet pipes. Loosen the hose clamps and slide them along the hoses toward the front of the vehicle.
- 2
  Remove both hoses from the heater core pipes, or nipples. Place the garden hose spray nozzle up to one of the nipples. Slowly open the spray nozzle while watching for water exiting the opposite nipple. There is no clog if the water flowing out matches the water volume being applied.
- 3
  Increase the nozzle opening if little or no water flows from the core. Apply the spray nozzle to the opposite heater core nipple, and increase the volume of water from the nozzle. Keep alternating the spray nozzle between the nipples to work the clog loose. You may need to remove the heater core to clear a clog that persists.

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