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No coolant flow to the heater core?

I have a 98 ford expedition that is not getting coolant flow to the heater core. I believe the supply hose comes from the water pump. The car does not overheat. Can the water pump be bad?

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If the vehicle is not overheating the waterpump is fine.  You can check it further if you were to crank it with it cold with the radiator cap off and watch it until the thermostat opened up (around 195 degrees F) if there is coolant moving then the waterpump is fine.

If when you turn the control on the dash from cold to hot on the temperature range and if you don't feel much or any resistance in the knob then your problem is that the control cable or hose has come loose and the valve that opens up to allow water to the heater core is not getting the signal to do so. If there is resistance and especially if you hear a click this is not the issue. It could also be at the other end of that cable or hose at the valve that opens to let the water in to the heater core. That should be under the glove box (check your repair manual for exact details).

Then I would check for a kinked hose and if there is none disconnect the two hoses to the heater core and back flush the heater core using a waterhose on each pipe until the water flow clean and freely. I suspect someone has used stopleak in your vehicle and if someone puts just a little too much in the first thing to clog up and stop working is the heater core which would cause this exact problem.When you back flush it and get it flowing again watch for leaks (If someone used stopleak there was probably a leak). A leaking heater core is evident when the inside of the windshield gets a little damper than normal because water mist is being blown onto it. You may also notice the carpet on the passenger side is damp if there is a leaking heater core.

If you end up replacing your heater core because either it has a leak that was clogged and now leaks after back flushing it or you can not get coolant through it even with the hose, you should probably have it repaired because typically a lot of the dash has to be removed to replace heater cores and it is a pretty tough job. Check your repair manual to see if you feel up to it yourself. If you do you can save a lot of money but it is often a real pain to do. I hope this helps.

Kaiser Willy

Thanks for this great information.  I will research how to back flush.  If I do have a leak can I use stop leak to fix it again?  i really cant afford a mechanics help right now.


One easy check for coolant flow through the heater core is to feel the two hoses to the heater core. Under the hood on the firewall. If they are cold after the engine has warmed up, there is no flow through the heater core.  If they are both hot or very warm, the water is flowing. On most later model Ford products, the water flows through the heater core all the time. Only the air flow is directed either through the heater core or not.

the solenoid that allows hot coolant to flow in the heater core is not working properly. Another possible reason is that you have a damper door that is stuck open, if its stuck open you may not feel warm air coming out of your vents.

Your auto repair advisor

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