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Interior Heater in 65 Mustang w/289

New User
Posts: 2
Joined: 12/12
Posted: 12/16/12 12:13 PM

We have no heat in the interior of my daughers 65 Mustang and are set to replace the heater core thinking it was plugged.  However, once we drained the coolant I could blow through the hoses and move fluid out of the core and then air.  Seemed completely free and clear.  We had replaced the therostat and done a flush a while back but when completed the car ran at operating temperature well so I do not think it was vapor locked.  

Before I pull the core...any thoughts?  

Post Reply
Posts: 455
Joined: 04/12
Posted: 12/16/12 12:52 PM

check for water flow... remove the thermostat and replace the thermostat housing.. start the engine and see how fast the coolant or water circulates through the radiator..

water pump blades have corroded away..  reducing the flow..

the water pump pushed water into the block around the cylinders.. up the back of the block into the head.. forward into the head/s until it gets to the intake crossover .. from there it is stopped from flowing into the radiator by the closed thermostat.. there is a bypass hose from the small nipple on the thermostat housing to the water pump.. this allows coolant to circulate through the system.. equalizing the coolant temps and picking up more heat until it reaches the opening temp of the thermostat..   when this happens. the hot coolant swaps with the cooler coolant in the radiator.. that cooler coolant enters the system and closes the thermostat.. allowing the cooling system to circulate picking up more heat until it cycles again..

when the hot coolant is allowed into the radiator and the cooler coolant gets into the engine and closes the thermostat..  this stops the coolant in the radiator so the fan moving the air through can remove the heat. ram air through the radiator also removes the heat..

lets talk about the heater core...

the heater hose is connected behind the thermostat..  so the increased mechanical pressure created by the pump pushing against the closed thermostat pushes warm to hot coolant through the heater hoses and the heater core where the heater fan can blow through it warming the interior of the car..

you can do the test above.. without removing the thermostat.. by just removing the heater hose from the intake manifold fitting.. adding additional hose to the manifold fitting.. plugging the end of the hose into the heater..  placing a gallon or 2 gallon bucket under the extended hose.. or directing it back into the open top of the radiator..   start the motor.. do you get a nice flow of coolant???  it will come through really fast... so just a few seconds will be needed..

lastly... aluminum oxide...  when coolant does not get changed often enough..  it can become acid...  it can dissolve the soft aluminum parts from the timing cover.. water pump.. thermostat housing.. it can deposit the aluminum oxide onto the interior of the radiator and the heater core..   aluminum oxide is a ceramic version of aluminum.. its a really good insulator.. so the hot coolant passing through the heater core is NOT in contact with the conductive brass... no thermal contact means no heat to the interior of the car...

if you have an infrared temp gun.. you can measure the temps of the heater hoses in and out of the core with the temp lever to HOT and the fan on high...  there should be a difference..

lastly.. once in a great while.. debris will get into the heater box and block the openings of the heater core... so no airflow..  

Post Reply
New User
Posts: 2
Joined: 12/12
Posted: 12/16/12 04:55 PM

That is a lot of information..thanks.  I went ahead an pulled the heater core and the entire heat box.  I am going to replace all gaskets and hoses.  After the rebuild we will reinstall.  Once I refill the antifreeze I will run the checkouts you describe if we are still not getting heat:
1) Remve heater hose from the intake manifold fitting and plug.  Add extra hose to manage water to the manifold fitiing and look at flow..should be high volume.
2)If the buld up in the core the problem would have been solved with the replacement of the old core.

Thanks again.  

Post Reply
Posts: 1410
Joined: 03/08
Posted: 12/17/12 02:21 PM

Before you go to a lot of trouble just make sure the hose fittings on the engine aren't plugged up- it happens if the engine has been allowed to rust severely.  

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