Is the heater core bad, the water pump or head gasket?

Asked by Apr 20, 2015 at 09:25 PM about the 2003 Mercury Sable GS

Question type: Maintenance & Repair

I'm losing antifreeze. Traveled 30 miles to work.  25 miles into the ride the thermastat rose nearly to the H.  It was about a minute after I turned on the heat and then traffic came to a stop on PA tpke. I turned off heater. Traffic was stop and go for next 5 miles. Thermastat stayed about 3/4 of the way up and crept a little closer to the h a couple times. After I got to work, Thank God, I noticed antifreeze reserve tank was empty. Waited a couple of hours and then filled with gallon of antifreeze and a gallon of water. On way home the thermastat stayed at 1/2 way, where it normally is. I did not turn on the heater at all.  I did smell some antifreeze though. And when I got home I added another 2 gallons of water. I noticed it leak once while looking at it for over an hour with my cousin, a mechanic.  It only leaked once and it was after I turned on the heater. But I turned off the heater and it stopped leaking.  We didn't see a leak for the next half hour, even after turning the heater on again and driving it around and going up to 60 mph. I drove home from my cousins for another 5 miles and still no leak.  Is it heater core?  Is it head gasket (engine doesn't really misfire but does seem to have a vibration) is it water pump?  Can't tell where it is leaking but it is toward the gack and side where water pump and heater core are and sort of behind the engine. No visible hose leaks.  162K miles 2003 Mercury Sable 6 cylinder. Again heater was not on at all when I traveled home some 30 miles and still lost 2 gallons of fluid.

2 Answers


You have to identify where the leak is. If it was a heater core, you would have coolant on the passenger floor or film on the inside of the windshield. Sounds to me like a heater hose or water pump is leaking. You'll need to pressure test your coolant system to help find the leak.

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Ford always tended to use pieces of steel tubing connected by hoses throughout the engine compartment. In areas of high heat, it doesn't take much for the hoses to break down and get pinhole type peaks around the ends where they are attached to the tubing with the hose clamps. These leaks along with the heat tend to corrode the ends of the tubing inside the hoses from the end of the tubing into the very tip of the steel tube. You could just have a leak caused by the corrosion inside the tubing ends, which you can sometimes eliminate by pulling the hoses off the tubing and then cleaning the tubing ends with some plumbers grit cloth. I would suggest that you try removing the hoses one at a time, clean the ends up and also check for pinholes in the length of the tubing ends where it is covered by the hoses. I would also changed the hoses with new ones as long as you have them off. If you do find pinholes in the tubes you could use a 2 part weld like JB and resurface the ends with it, allow it to dry completely then resurface it very smooth again using the plumbers grit cloth. The leaks are probably on the ends of the tubing back near the fire wall or on the steel nipples that come out of the fire wall from the heater core.

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