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Topic: Coolant leak only with heat on. (Read 1298 times) previous topic - next topic

Coolant leak only with heat on.

87 Bird with 3.8 from what I found in the search I am now a bit puzzled. I found that coolant will flow thru the heater core at all times. This car makes heat and doesnt run hot and is full of coolant. If I turn on the heat it spews coolant out the case drain to the outside(at the firewall) I know it needs a core but my question is why doesnt it lose any coolant when not using the heater since coolant still flows thru.

Coolant leak only with heat on.

Reply #1 –
Good question. On mt old '87 Cougar, that happened when I turned the air on, right above my right leg coolant only leaked when I had the air on, never figured out exactly what was wrong, but I put some radiator stop leak  in it ( not the bottled stuff, it was some little gold tube....) and it never happened again. Maybe once you replace the heater core it will stop.
FOXLESS!!

1994 Lincoln Mark VIII

Coolant leak only with heat on.

Reply #2 –
Quote from: Dansbirds;265955
87 Bird with 3.8 from what I found in the search I am now a bit puzzled. I found that coolant will flow thru the heater core at all times. This car makes heat and doesnt run hot and is full of coolant. If I turn on the heat it spews coolant out the case drain to the outside(at the firewall) I know it needs a core but my question is why doesnt it lose any coolant when not using the heater since coolant still flows thru.


Because of FM.

F'ing magic,,,,,,,,,, oddest thing ive heard in a while on here.
Just pulling ideas from the air,,, years ago there was a diverter type valve that manuall allowed fluid to flow through the core via a console controlled heat selector cable.  I think my wifes 1990 bronco has this feature.

If somone installed this or something of the like on your car, you have your answer.  I think it was a stock item on many older cars and I think its a great idea to this day.

Coolant leak only with heat on.

Reply #3 –
I can see the magic as a possibility. That would also explain how this 3.8 keeps going and going and going....  I will be putting a core in it as soon as I go get one so we shall see whats in there then.

Coolant leak only with heat on.

Reply #4 –
there should be a valve in your heater hose near the firewall that only opens when the heater is on unless someone has removed it for some reason this would be why you only get coolant with the heater on.  this has been on all ford cars since the 70's or longer...

Coolant leak only with heat on.

Reply #5 –
Quote from: Dansbirds;265955
87 Bird with 3.8 from what I found in the search I am now a bit puzzled. I found that coolant will flow thru the heater core at all times. This car makes heat and doesnt run hot and is full of coolant. If I turn on the heat it spews coolant out the case drain to the outside(at the firewall) I know it needs a core but my question is why doesnt it lose any coolant when not using the heater since coolant still flows thru.

Could it be that when the blower is circulating air through the heater core it blows the leaking coolent out into the case.
With no air through the core the leaked coolent just stays in the core and evaporates.
Of course this would be a slow leak.

Coolant leak only with heat on.

Reply #6 –
Quote from: 88turbo;266037
there should be a valve in your heater hose near the firewall that only opens when the heater is on unless someone has removed it for some reason this would be why you only get coolant with the heater on.  this has been on all ford cars since the 70's or longer...


enlighten me,, never seen it.  maybe i miss that on all my previous cars.

on a stock 3.8,, the metal tubes transition along the intake up to where some very small elbow hoses tie in the core.  Ive never seen what your talking about on these cars.


Dan
Examine your hvac box with the glove box out.  A gal named crystal on here was able to cut the box (ie- cut 3 sides of a rectangle shape) and then was able to pry open the duct in order to extract the core.  I keep passing this trick along but yet to see anyone attempt it.  She said she then duct taped the flap shut.  She didnt have to remove dash bolts and the such per the coolcats link.

Ive looked at it in great detail and can see where the hvac box could be cut, wish she would've posted pics of that so long ago.
 

Coolant leak only with heat on.

Reply #7 –
Quote from: 88turbo;266037
there should be a valve in your heater hose near the firewall that only opens when the heater is on unless someone has removed it for some reason this would be why you only get coolant with the heater on.  this has been on all ford cars since the 70's or longer...

You may be thinking of the "ATC thermal blower lockout switch".
It has a switch that keeps the blower from running when the engine is cold. It also has a vacuum valve that keeps the recirculate/outside air door in the recirculate position with a cold engine.
It's part of the ATC feature.
It has no effect on coolent flow through the heater core.