Head Gasket leak? Overheating....

hey guys, any feedback on this problem would be helpful. When i drive the temperature will go all the way to near overheating. THen sometimes it will dramtically drop or it will get hot and ill have to pull over. When idling, its fine, its when driving that it gets real hot real quik.
Basically, it gets hot quick and will fluxuate. Also, the heater doesnt work when it does this. But when it cools down and runs right the heater does work.

also, i changed the thermostat, but couldnt purge the air becuse the screw broke and i havnt had a chance to tap it out and replace it. it still does it with a new thermostat.

thanks guys

How long has it been since you changed the thermostat ?

Air locks can be a real bitch - they stop the coolant from flowing or being pumped properly.

actually i changed the thermostat today. It was a real bitch. what i noticed before was that, the car always rean real cool. Like at the first mark. the thermostat i got was a 190 degree thermo. but when it idles it is around 220. then when you drive it gets hot and fluctuates.

alot of air came out the first time my friend and i purged it. then the screw broke off and we could purge it again.

Sounds like an air lock - the air will find the highest place in the cooling system (usually were that screw is located) and stay there.

I would replace the screw before you do damage.

I have seen a mech. rock the car up and down trying to get it to 'burp' using his knee on the bumper, but it's a long shot at best.

Is that screw inside a larger screw ??? if so undo the larger one carefully - it will purge that way as well.