gurggling noise coming from the heater core area

i top it off and run it for the day, then next morning i am low on fluid, no signs of leaking anywhere, i layed a piece of cardboard on my floor in garage and parked over night and no leaks, but low on fluid again. I check my oil and no milky residue, the oil level is consistant full. The garage costs me $200 so far and still cant figure it out. The prob. is not that big of deal right now, truck drives fine, but its something that is bothering me. thanks

The most common cause for mysterious loss of coolant is a headgasket problem. Has your shop checked for ehxaust gases in the cooling system?

the next thing they wanted to do is pull my spark plugs and turn the truck over and see if coolant squirts out, but the charge is 250.00 just to do that. i think you are right my head gasket or a cracked cylinder wall and coolant is going into piston area and out my exhaust or burning up. thanks Russ your comments help me decide what to do from here