ok, i like to think of the gf'* bonneville as a delicate egg. If i had the time and money i would do all the required maintenence on it but i don't have either so i am forced to keep the car at a "decent" mark of running condition. so here'* the story. i gave blood and got a free oil change at a local chevrolet dealership. i do my own oil changes on my alero but i haven't had time to change the oil on the gf'* bonneville and it was 1500 miles overdue. so, i decided to use the free oil coupon that i had today. first, i take the car in and the lady gets the work order all situated and tells me that car will be ready in a half hour. one hour passes and i haven't gotten the car back so i ask whats taking so long. lady says "well, the coupon you gave me also included a lube job and the fluids to be topped off. so i was like "oh don't worry about the fluids" but she said they had just finished it. so i get the car back and i am driving it home and temp gauge gets to the "3/4" mark and it rarely goes over the 1/2 mark. so i think nothing of it, then remember how nasty the extra coolant resivoir was (it looks like somebody puked in the tank). so i get the car home and pop the hood. resivoir tank is still mostly empty and nasty looking so i don't think they messed with it but i can tell they topped off the other fluids because the power steering is a little over-filled now. i also looked at the oil filter and it looked like it could be leaking a little at the top. then i took the car back to the gf'* house and on the way, heat started blowing cold. i was like "wtf"? its working again but why did it stop? did they screw up something with the anti-freeze?

They probably pulled the radiator cap off and not the reservoir tank. You might have an air block in the system. Add coolant to the reservoir to the cold or hot mark as appropriate. then you can burp it from the top of the t-stat housing, or warm the car up and squeeze and release the upper radiator hose a few times to try and move the air blockage through the system.

When the engine has cooled, open the radiator cap and look at the fluid. If it'* low, top it off. What your saying sounds like low coolant.