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I own a Mustang II 1974 v6 2.8 and its overheating bad but not allways!!?? I put a new water pump 2 cooling fans, new thermostat (188-195F) put anti freeze 40% check fot blown cyl head gasket, hoses r ok and is still overheating.My mechanic says i need a maybe new radiator because it might be blocked but i dont think so because if i remove the thermostat the engine is freezing whoch meens water cyrculate.2 thngs are strange: 1 some days temperature is stable in the normal limits and others becomes a volcano after 5miles open road and winder time.Second if i toutch with my hand the radiator when is overheating the upper half part is very hot and the bottom half is completely cool! Also when overheating and i open the radiator cap the fluids r boiling and a lot of steam comes out for minutes.Someone toldme i must bleed the system from air! Could that be and how i can do it?
 

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hot water is pushed into the top of the rad the cool water is pulled in from the bottom their is a blockage some where in the rad. ( when the coolant is cool take the rad cap off and squeeze the upper and lower rad hoses this moves the coolant around and should move any air pocket)
 

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This engine the thermostat is in the lower radiator hose, not in the upper. Some people take off the top hose and see no thermostat and then put one there. There is none, its in the bottom hose, and you must take air out of the system when you change it. I usually drill a small hole in the thermostat to help bleed air out. If you did this correctly, I would try a new radiator
 

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i would recommend the rad and a flush , also get a new temp sensor and gauge ( aftermarket ) , I've had to park on a hill and when cold , open the rad cap and fill it , letting the car warm up with the cap off to get rid of a stubborn air lock . good luck
 

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Underneath the front end of your car is a plastic piece called an air dam and is located on the bottom of your radiator core support. What it does is force air up into the radiator while driving . If it is gone or tattered from going over something that could possibly tear it off or if its tattered then it can't force air up into the radiator. Because of the design of the front end of cars in the 70's Ford and GM had to put this air dam under there. At slower speeds ya don't need it but at higher, open road driving the air doesn't get up into the radiator and the way you describe your overheating problem I would say this is the problem
 

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you have to have a blown head gasket you just dont see it. Its not always obvious and sometimes you can check and check and swear you dont have one. Ive had the same problem and sweared up and down the head gaskets where ok but it was blown. As soon as I changed them the problem went away but it also could be your intake leaking antifreeze too but first make sure your carburetor isn't running lean time to time. Mustangs 2 are ok cars i want one
 

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Yes air very easy to correct remove radiator cap start engine let warm up so radiator is flowing and air bubbles will come to top. newer cars have peacocks same princable except you release air like bleeding brake in faked peacock bleeder valve looks same as brake bleeder valve. and some times you get a defective thermostat. P.S. once air is all released top off radiator.
 

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I have a 78 mustang II . I had a overheating problem last fall, change your rad to a double core and check your fan shroud if it is broken it might not be getting enough air to cool the rad.
 

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Replace the bottom hose.

The top of the radiator is hot, while the bottom of the radiator is cold. That means the water is not flowing properly.

Blown headgasket, radiator too small, shroud broken, etc, ad infinitum, do not explain the radiator thing.

You say that after five miles of open road driving and it overheats. Well, its the bottom radiator hose. It's collapsing when the engine revs harder causing the water pump to pump harder but that just increases the vacuum inside the bottom hose caused by the engine trying to get coolant.

I reckon the interior lining of the bottom hose has come away from the rubber and is collapsing when the speed of the water flow increases when the engine is revved up.

I will guarantee that the times when it runs in the normal range is the days that you are not driving on open road but in the suburbs and not having to rev the engine higher.

Do this simple test:

Let the engine idle until its warm (you want the thermostat open). Take the radiator cap off and look in. You should see the water flowing past the opening. Rev the engine up to about 3000rpm (about the rpm you would be at while driving on the open road) while you watch the water. You should see an increase in speed (of the water). If not, then you have a problem with the bottom hose intake. Replace it.

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ist and easiest thing to do is go to auto parts store and have them test your radiator pressure cap for the pounds of pressure it will hold and compare it to the factory specs. If its off change it. I had a 390 Ford i owned for 15 years and the cap became faulty after many years it took me a while to find the problem. It had the same diagnosis as yours. This maybe a cheap and easy fix for you.
 

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I do believe you have air in the cooling system. One way to remove the trapped air is to disconnect one of your heater hoses at the firewall. Then proceed to fill the engine with coolant till the antifreeze comes out the hose. then reconnect the heater hose and run the engine without the radiator cap on until the thermostat opens . You van tell when that is by the coolant moving in the radiator. You may hear a gush when the thermostat opens and the air comes out.
Now stop the engine and finish filling the radiator install the radiator cap and fill the reservoir to the fill line.

The other possibility is that your lower radiator hose is collapsing. squeeze on the lower hose if it collapses in your hand replace it. The lower hose should have a spring in it to keep it from collapsing (warning some cheap hoses do not have this). The water pump sucks in the coolant from the lower hose and if the hose is weak and you rev your motor (IE drive on the freeway) the suction will cause it to collapse.
 
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