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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8622
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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2003 Mitsubishi Galant: stopped working..thermostat..the heater core

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I have a 2003 Mitsubishi Galant and the heat stopped working. We put in a new thermostat and that didn't work. I am reading that the heater core is a common problem with this make/model. Do you have any idea how much this repair will cost?

To replace the heater core you should expect a repair bill in the neighborhood of $730. This consists of 5.2 hours of labor and $205 for the heater core. If you opt to install an aftermarket (non-Mitsubishi) heater core, you can typically cut the price of the core in half. The reason for the high labor cost is that in order to remove the core you must remove the dashboard, crash bar, discharge the AC and remove the entire AC/ventilation box.

It is important to note that the heater cores in these cars do not typically need replacement except when they are leaking. You should check both of your heater hoses to verify that they are both hot. If they are, your problem lies in the temperature blend door or the cable/motor (depending on your trim level). If the hoses are not both hot, specifically one is hot and the other isn't, you should first try back flushing the core to clear any obstructions. If you can not flow any water through, you have either an obstruction in the core or a bad heater control valve (which is fairly common). If some (dirty) water comes through, there is an obstruction that can usually be cleared by continued flushing, or replacement if it will not clear.
Customer: replied 6 years ago.
Thank you for your response - if it is the heater control valve, would the repair be just as costly??

The labor would be the same, and the parts are $136 for the control valve motor. A crafty tech could shave the time down to 2-3 hours if they wanted to however, as you can partially remove the dash and sneak in there without tearing everything down. Technically, it is a 5.2 hour job by the book though.

Do the flow check first, the majority of the time these problems are just some gunk blocking the flow through the core, or there is an air pocket in the heater core preventing adequate coolant to flow through it. While these control valves do go bad, it isn't nearly as common as a simple air pocket, blockage, etc.
If you have had any coolant related leaks in the past season, this would be enough to cause the condition. It is very common for the radiator hoses on this model to leak at the engine end (the hose end will swell up, and green crust will start to form at the end of the hose). By the time crust starts forming, the heater efficiency usually goes down hill..
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