[cooljess76]

When I first got my car, it had a tiny hairline crack on the radiator next to the expansion tank. It wasn't big enough to show signs of any leakage, it only leaked when the engine temp was warm and even then, the coolant evaporated before you could see it. I experienced the no heat issue at the worst possible time(driving cross country through an ice storm).

As soon as I seen the needle begin to rise, I pulled over, let the motor cool down and added coolant. Did this a couple times during that trip until I finally read about bleeding the cooling system. As soon as I bled the cooling system, my heat returned. At that point, I didn't know that my radiator was cracked. I did however check my coolant level everytime I stopped for fuel and it continued to need topping off. Made it home with no problems, again topping off the coolant whenever possible.

Once home, I looked for leaks and found nothing. Drove the car for a couple thousand miles, everyday observing that the coolant level continued to drop. Friends, family and forum members all swore up and down that I had a blown head gasket. However the car continued to run fine, no smoke, no coolant/oil mixing. Still continued to drive it, topping off once a week. Eventually it got so bad that I was topping it off daily.

Two oil changes, almost 10k miles later, it still showed no signs of a blown head gasket. Nobody could explain where the coolant was going. One day a friend and I rigged up a pump with a fitting that threaded onto my radiator cap. I pressurized the system to about 10psi and listened for leaks. That's when i found the crack next to my expansion tank.

I was so cautious, that my car never once overheated. Even the time during my adventure across country when I bought the car, the needle only began to rise. The whole time I knew I had a problem, but I watched that needle like a hawk. I checked the coolant level EVERY DAY! When it dropped, I topped it off and bled it. I even got sprayed in the face with boiling hot coolant at one of our SoCal meets! But I still topped it off.

My point, even the tiniest of undetectable leaks can let coolant out which in turn leaves an air pocket. If let go long enough without bleeding, it'll eventually cause air-lock in your radiator and coolant will not be able to circulate. That's why your heat stops working, there's no coolant flowing through the heater core.

My suggestion, bleed the cooling system thoroughly and monitor the coolant level daily. It may take a few good bleeding sessions to remove all of the air. Repeat the process several times. If you continue to lose coolant, it's time to start looking for a leak. There's a couple plastic coolant lines that are known to crack. Also, your radiator could be leaking in an area that is not visible.

Perhaps you could rig up the same type of tool that I did to pressurize your radiator and listen for leaks. If you do that, I suggest doing it indoors because the hissing will be very faint. Good Luck, sorry for the long post.