Ok...here is what happens...

My 94 Civic EX 1.6 Vtec appears to be overheating. The temp. gauge does not go past it's normal point about 1/3 the way up. I've replaced all heater hoses as well as rad. upper and lower. I've replaced the thermostat and gasket. A block test was passed showing no combustable gasses in the coolant. Now, with the radiator cap off, the cooling fan comes on....like it should. However, if it were to continue to idle, the coolant just starts boiling out...like it is drawing air from somewhere. With the radiator cap on...coolant just boils out into the overflow tank and when that fills up, coolant is sprayed throughout the engine bay. The head gasket has recently been replaced...the head was also machined at that time. I fix customer cars on a daily basis, but my own has got me stumpped. Any advise or suggestions would be greatly appreciated.

 

did you pressure test the rad cap?

 

No, I didn't pressure test the cap...didn't have the proper adapter...but then why do air bubbles still present themselves with the cap off? If I leave the cap off, the fan comes on and then afterwards...coolant just boils out until the radiator is almost empty.

 

you must bleed the system while adding c..c..coolant waterboy make sure you have no air in the coolant system. use the bleeder screw near the thermostat.

hope it helps

Did you let someone else do it for you, or did you do it yourself??

 

I did all of the work myself...but no matter how long i let it run...the bubbles do not disapate, i've bled it out the bleeder screw and out of the radiator...the only think i haven't done yet is use an airlift to vac the air out of the system...but that still does not explain why it keeps boiling out of the radiator with the cap off??

 

Change your radiator cap. Its seems that its not holding the pressure. Also double check the headgasket because it make be causing the overheating. I just finishing fixing a car with the same synthoms and its was the head gasket and radiator cap..

 

you will always get some bubbles coming up even if the system is bled properly. the high temperature of the water, combined with low pressure generated by the water pump causes cavitation, just like the trailing edge of a boat propeller under water. If your radiator cap is good, you have no leaks in your system, and if your radiator is not too old (still has fins) I wouldn't worry about it. The air bubbles will find their way to the top of the radiator, leak past the cap, go to the reservoir and bubble out when hot. When everything cools and contracts you will suck water back in from the reservoir. It is just a vent and buffer for the coolant.