Warrior_84

A little while back I posted athread about the heater core: "while traveling I was using the heater and I was losing coolant like crazy. I could also smell antifreeze in the cab so I thought it was the heater core. As soon as I stopped usingheat I didn't lose near as muchantifreeze."Well nothing was draining from the little plug in the firewall below the heater core. We couldn't find any leaks while the heater was off but when the heater was on the overflow reservoir was overflowing. Isn't the overflow reservoir supposed to be pressureless? What could be causing this? I'm not blowing white smoke out my exhaust. My exhaust doesn't stink. My engine oil looks good. Any ideas? Any help will be much appreciated!!! It's a 1991 Mustang GT 5.0

ewgoetz

Did you have the system presure tested?

Warrior_84

Yeah... It held pressure until I turned the ***** to heat (key still completelyoff) then it would drop down a few pounds but it wouldn't completely lose pressure...

Warrior_84

Oops, also, I couldn't tell where the leak was...

mjr46

with the system pessurized...can you see any leaks externally???... try a new radiator cap...or you may have a restriction in the system somewhere

Warrior_84

Well after some more looking around it looks like the coolant is leaking out the top back part of the engine... Like the intake gasket...? Is there a diagram around that shows exactly where all the coolant lines run? It looked like the leak was too high to be the head gasket... I don't know... Like I said earlier it's not blowing white smoke and the oil still looks good... And the leak stops dripping when the heater is turned off. Any ideas? Do you think it's safe to continue driving it until I can pinpoint the problem and get it fixed? It's my daily driver. Thanks again for all your help...

Lee

Mustero

Pressure check the system again & pay special attension to th eheater hoses.Sounds like maybe a leak after the heater control valve before the firewall. Hope this helps

Warrior_84

It wasn't leaking from either hose that comes off the heater core (or the other end of the hoses). Where's the heater control valve located? Thanks again!

capri debris

The heater being on or off has nothing to do with a leak or pressure in the system. There is coolant running throught the core at all times... the heat controls only move flaps inside the heater box to direct the air... they don't allow or stop water from flowing though the heater core. And no, the overflow is NOT pressurized. Just take a look at it and use common sense, there is a port at the top that is open to the atmosphere... why would you think it is under pressure? A blown head gasket does not always mean coolant in the oil. The head gasket can blow betweena cylinder and the water jacket and doesn't affect the oil passages... just lots of white smoke when you start it and then when youdrive it, it will pump all the coolant into the overflow from the cylinder pressure being higher than what the radiator cap is rated for. Only when the gasket blows between the oil passages and the water jacket do you get coolant in the oil. It just sounds like you have a leak at the intake mainifold or the small hose that runs from the back of the throttle body... it could also be leaking where the heater hoses connect to the two black metal heat tubes that run under the throttle body.

mjr46

there is none!! pressure test it and use a mirror to see the leak