Good Evening... interesting one here... for me anyway...

My wife went out with my 2004 Hyundai Elantra yesterday afternoon and on her way home she heard a loud bang and smoke or steam started coming out of the engine compartment. She immediately pulled over fearing the worst, and got towed to our nearest garage. I went over after dinner and had a look. I could see lots of collant had leaked out but nothing obvious as far as damaged hoses or line. The only thing abnormal I noticed was that the cap on the overflow bottle was no longer secured. Immediately I thought maybe that was what she heard and what caused the steam and spilling coolant, but nonetheless I disconnected all of the hoses, lines, and electrical, and I removed the Radiator from the engine compartment. I removed the fans and inspected the rad to the best of my ability and found nothing wrong. All hoses and lines check out also. By the way, the hose coming out of the bottom of the radiator was still full of coolant, and there was still a fair amount of coolant in the radiator (though I could not see any when I initially took the rad cap and looked inside)

I have since put the rad back in the car and driven it back out into the street. I plan to go get some coolant tomorrow, fill it up and give it a whirl to see if I have a leak anywhere.

So, the ultimate question is this: could the cap on the overflow popping off have caused all that ruckus and a ride behind the towtruck?

Oh one more thing. On the passenger side of the car, two metal lines run into the rad. I unbolted them both but had difficulty taking them off. As I tried, one of them popped and released a whole lot of pressure and fluid. Afterit stopped (5-6 seconds), I was able to remove the second one without incident. The one that released all of the pressure has a small cap on it marked with an "H", and when removed it reveals some sort of valve. Was I supposed to release that pressure before removing the line?

Please let me know if you've experienced this and what else I can check.

Thanks, Pat

Before installing any coolant you should think about filling it with water and pressure testing the radiator. Make sure there are no seam leaks.

You have a major cooling problem that caused the pressure to go real high and blow the top off the overflow tank. Check to see if the water pump failed. See if these links offer any help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post235973

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1365453

The two metal lines likely went to the automatic transmission. ATF enters the radiator to be cooled.

Could be as simple as a thermostat. Let's hope for the best.

Simple problem... radiator was cracked all the way along the top of the plastic container. New rad is in and working great. Now I just have to get the A/C fixed up in the spring and I'll be all set.

Thanks for the posts.

Pgerard, What caused the radiator seem to crack, My first thoughts were to replace the thermostat also, which could very well be the culprit, thermostat never opened thus causing the split, The pressure and fluid thing was freon and the oil in the air conditioning system from the evaporator, which is mounted near the radiator and often mistaken for just that, the radiator, good luck

Pgerard, What caused the radiator seem to crack, My first thoughts were to replace the thermostat also, which could very well be the culprit, thermostat never opened thus causing the split, The pressure and fluid thing was freon and the oil in the air conditioning system from the evaporator, which is mounted near the radiator and often mistaken for just that, the radiator, good luck

One thing about some modern radiators that contain plastic. They can loosen on their own from the expansion of normal use. Since the OP mentioned plastic radiator in the same sentence. It just may be fatigue is the only culprit.

It was the thermostat that was stuck, so it was replaced. That's what the mechanic told me.

Thanks for your comments guys.