Ok, I dont understand this so maybe some one can help. I recently had the head gaskets replaced on my car along with the water pump, timing belt, thermostat, both radiator caps, both hoses, and the radiator. I started noticing that my heater was not heating up very well. So I made sure the radiator was topped off. The heater got a little better. Then I notice that the radiator overflow tank was overflowing.

I took the cap off it and noticed that the mechanic removed the straw attached to the cap that feeds the antifreeze back to the radiator. So the overflow tank was just overflowing without any way to get antifreeze back into the system. So I added a tube and filled it up. Next thing I know at a red light I notice the temp gauge going up to the hot level, I started moving and the air brought the temp down before it got too hot, it went right back down to the normal level. I get home and the overflow tank is overflowing again.... So I get the radiator caps checked and one of them was bad. I replaced it.

Everything is now fine. Until I drive it for about two hours, then the heater goes cold and I notice again the overflow tank is overflowing.....


Arggggg!!!!! It did not get hot at all but the tank is certainly getting all the antifreeze and just blowing it out. I checked for leaks and there are none. I checked the heater core and there are no leaks there either. I see no signs of a head gasket leak again. What could it be???? This is driving me nuts...

 

Replace both radiator caps .. Had the same promblem with my previous lexus I owned.

 

check thermostat............usually quite simple in other vehicles (not quite sure about ours though) relatively cheap part and install.

 

Its probably either the heater core (behind the dash) or heater valve.

 

Better park it.
Sounds like the coolant system needs to be purged of air 2 me.

 

Well it turns out both my radiator cap and the upper filler cap were weak and caused the lack of pressure which led to the boiling over. Once I replaced them it is fine but I have a small leak in one of the heater hoses I need to fix. Thanks for your help and remember to check the radiator caps first if you have a similar problem.