Ok here is the story, about two years ago my car was running, and developed a problem where by the cooling system would get huge air bubble in it, no matter how many times i filled it, it would always leave me stranded on the side of the road overheated.

So i bought new radiator caps, to no avail, all arrows pointed at a blown head gasket. So out with the 3.4 and in with a new 3.8sc.

I still have the same problem, all i want to do is drive my car, but i cant because it overheats... the water isnt leaking out. Its just disapearing????

It's either leaking, or burning, Water is matter, and without certain nuclear processes it's impossible to convert it to energy.

Likely it's only leaking out under pressure, hence no drips when sitting.

Invest in one of the UV dye tracer kits available at most auto parts stores and go looking for the leak.

Also, make sure you have the correct radiator cap, it needs to be non-vented and rated for 15 PSI.

James

Are you sure you got the correct radiator cap - the Stant catalog lists the wrong cap You want a NON vented cap. There is a good write up on that subject in Ogre's cave

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so what would happen if i had the vented cap

The vented cap (The one with the little lever on top) is 1 1/2 inches deep. The regular non-vented cap is 1 1/4 inches deep. Now I have never used the vented ones (they just looked funny) but I would guess you would have to press down very hard to get that taller cap on the radiator. What difference do they make? You got me. They are both rated at 16 psi, but as measured, would make it over pressurize if there is no room to expand properly.

Have you checked the coolant pipes under the car for bends or unseen obstructions. How old is the radiator and heater core, you may want to pressure test the system to find out whats going on, run the engine for 5 minutes, take out rad fan fuse and disconnect battery. Feel to see if the radiator has hot and cool spots on it.... Since you have swapped engines and it still does this, it has to be the rad, lines, heater core....

When you park with the nose slightly lower than the rear of the car a vented cap will allow coolant to siphon into the overflow bottle onto the ground as it cools off.

I've got a vented cap form Autozone and have no problem with it. I don't think there is anything basically wrong with a vented cap it's just that certain Stant vented caps were wrong for the Fiero radiator.

The vented cap is handy because when you fill the system you just

-jack up the back
-flip the lever on the cap
-fill with coolant in the back until coolant starts flowing to the overlfow tank
-unflip the lever on the cap
-fill til it's full in back
-run the engine and top it off in back

Initally you made mention of a blown head gasket. How can this neophite determine if my gaskets are blown and if it why I keep getting air in my system.

Thanks Matt

flush out the system
pressure test it
new cap
and "burp it"