Cooling System Pressure
 

If you've been following my Elantra saga, you'll know I have a 97 GLS with a 1.8.

We did (replaced) the timing belt, the water pump, the CCV valve, the PCV Valve, Tires, Radiator, Thermostat, Transmission Service, Oil Change, replaced broken Radiator Fan Motor, Fuel Filter, Spark Plugs, and oil change.

Since I got the car it always seemed to leak antifreeze. Initially we found the radiator was cracked, so we replaced it with a new one, and bought a new cap for it. Later the waterpump blew, and we replaced but the timing belt and waterpump together. I found the radiator fan motor was burned up, so I bought a new one and replaced.

The coolant continues to overflow from the cap. I'm starting to think maybe it's head gasket leak where exhaust is leaking into the cooling system. Car runs fine and the temp maintains at just under half. Any idea?

Can you smell exhaust gases coming out of the antifreeze overflow tank or see gas bubbling up through the antifreeze in the tank? If so, your suspicion about a leaking head gasket (or cracked head casting) are correct.

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I cant smell exhaust just the smell of antifreeze, that sweet smell. What I get is antifreeze coming out of filler neck from under the cap. When i park I usually get a small puddle on the ground.

Put your face in the exhaust pipe. Do you smell antifreeze?

If it's blowing antifreeze out the overflow, it's probably head gasket blowing pressure. Usually it works the other way, and antifreeze gets sucked into the cylinder, and out the exhaust. Either way, it's not a good thing. Fix it fast before is wipes out the catalytic converter and the O2 sensors.

Even though it is a relatively new cap, I'd inspect the rubber gasket in it and make sure it is the correct cap to begin with. I also think the line leading to the reservoir tank is plugged or pinched or the bottom of the tank has an obstruction. If so, then what you are seeing come out of the radiator neck is the normal expansion of the antifreeze. The system eventual gets low because it cannot recover the loss. Pull the tank and line and make sure they are clean. Also, inspect the hose barb on the radiator neck. These are molded plastic and there may be some flashing left inside the barb plugging it. Other than these thoughts, I am stymied.

Wrapping up
 

I hate leaving posts unsettled. So here goes!

Looks like the system was just overfilled. It has stopped overflowing from the filler cap. Seems like it was just normal expansion.

Thinking it was possibly exhaust in the cooling system because of the rough running and short stalls due to the purge valve. All items have been fixed. Motor mounts and tranny mounts are next up.

-Ant