Two months ago, i noticed the coolant overflew out of the coolant reservoir after a highway stop. I kept driving then on local street slowly and it became overheated, indicated by the temp needle. I immediately stopped and let it cool down. I then continued drive slowly and overheat came back. So I sped up and drove on highway, the temp indication came back normal. After the incident, i stopped driving long distance. I only drive 20 to 30 miles now and mostly highway. What I continue notice is the coolant continue to over-flow and you can see bubble (air) coming out of the rubber tube in the reservoir. That means the cooling system has constant air. Where does the air come from? I was thinking partial broken of head gasket, but there is no oil in the coolant. two weeks ago, my radiator broke. I think it was due to higher pressure plus new radiator cap I installed.

Two thing I did before this happened. I have the timing and drive belts, water pump and thermostatic replaced by a shop. I also drained the coolant myself. I possibly damaged something when i drained the coolant. I released the radiator drain plug with engine running and air conditioning on. I thought this could drain all fluid out of the engine. Did I damage any thing? Could the air conditioning system bleed air into the engine? My shop mechanics told me to keep driving until it overheats again. I don't want to drive long distance to make my car over-heat. What do you thing is wrong with my car?

 

Head gasket.. no oil because it hasn't reach to that stage yet, same thing happen to my car before.

 

Not overheating at highway speed suggests it may be merely that the fan does not work. But the head gasket is definitely possible too. Check that by opening the radiator cap cold, start the engine and rev it and see if air / coolant blows out.

 

Thanks. air/bubble blows out at the radiator. Small packet of air blows out every 2 to 3 seconds. I think it's the head gasket, too. But could it be the cylinder also?