Radiator Reserve Tank

remove items in this order and fit in reverse
1st-grill to help with access
2nd-cooling fan
3rd-fan shroud
4th-radiator hoses x3
5th-radiator
remember to remove the rubbers at the bottom of the old radiator to use on the new radiator

Does the temp gauge show overheat? If not, then you're not overheating. Possible you have a head gasket problem,which lets combustion gas into the water and can look like boilover.

If the fan doesn't come on when the temperature goes up, and it should, that's the reason it's overheating. Fix the fan or fan switch.

you are overheating. Check temp sender in block. Also make sure fan relay is operational in fuse box. Fans should come on after about 5 minutes of idle.

well the reserve thank usually holds excess water. basically when water gets hot it expands and increases in size, the expansion causes some of it to go into the reserve and it can be very hot even boiling..

did this happen before or is it strange ?
notice any other problems while driving around, noises, engine overheating ?
does the radiator fans turn on ??

The overheating could be a stuck thermostat, or a failed water pump among other things. If you are loosing coolant faster than the leak on the hose, you may be burning it out the exhaust pipe. Which would point to engine problems.
If the temp gauge is not showing the engine is hot, and the fan is not coming on, what you are smelling may only be the drip blowing onto the exhaust pipe. The engine may not be running hot.
A mechanic would use an infered thermometer or a scanner to "read" the engine temp to verify it is overheating.
There is a chance the system is not actually full and has air pockets in it which would need to be bled out.

Answer could be a faulty thermostat,or it could be a sign that your head gasket is about to blow ,or last of all your timing could be out of sync.

Answer 2 from Inventus: It means your cooling system is funtioning properly. In a system having a coolant recovery tank, coolant in the radiator is always up to the brim, hot or cold. There is negligible or no air space. When coolant in the radiator expands sufficiently due to warming from the engine, it will squeeze past the pressure cap's bottom seal and flow into the recovery tank. (If no provision for such expansion was present, the expansion would rupture the radiator or your hoses.) Only coolant within the radiator is under pressure, and because of this pressure (together with the elevated boiling point that the "anti-freeze" permits), it normally does not boil. But once past the pressure cap's bottom seal, the overflow is at atmospheric pressure and therefore boils.
This boiling is usually unnoticed after a short, i.e., local, trip because the cooler coolant already in the recovery tank quenches it. But after some highway driving the influx of more hot overflow heats up all the coolant in the recovery tank to the (unpressurized, i.e., "natural") boiling point.
As the engine cools when shut off, the contracting coolant in the radiator sucks back coolant from the recovery tank. Fluid in the recovery tank should never be below the "full hot" or "full cold" marks, lest air be sucked in.
-- BETTER ANSWER ==
Your cooling fans are not turning on. It is not normal for your overflow tank to boil like that. It is true that your radiator is overflowing into the reserve tank, but that means yourr adiaotor is boiling. Check for blown fuses or relays for your cooling fans. IF theya re fine. run your engine for about 15 minutes and drive. When you temp level is at normal operating temp open your hood with the engine runing and see if your fans are on. If they are, then you may have a bad thermostat or a plugged radiator, or a bad water pump. If the fans are not on, get your cooling fan switch replaced if your car has one. Check your temp sending sensor

Sounds like you have a clog, or a collapsed hose. Try flushing the system.

When the car is completely cool,check the electric fan(s) for smooth rotation.

Clean/check/change the thermo sensor,contact and wire.

===

Excavate air pocket in coolant system / check for head gasket leak

This test will kill two birds with one stone.

===

MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!

RAN THIS TEST IN A WELL VENTILATED AREA ONLY!

You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!

===

Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Top of the coolant reserve tank

Let it ran for 10-15 minutes.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.

If you do not see any in rush of bubbles then your thermostat may be partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat host few gentle taps.

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

Let engine cold down and top off coolant reserve tank.

Start monitor for coolant lost

===

A coolant flush is require every 2 years or 24,000 miles.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.

===
Please post more information by clicking the comment link on the top right corner.

DON'T FORGET to RATE ME if my tip is helpful to you!

When the engine overheats, steam moves to the reserve tank to relieve pressure in the system, and can seem like it is overflowing.

Civic cooling systems always require an auxilliary fan or blower. Have this checked for serviceability. If the aux.fan is working properly, this points to other problems with your cooling system, which may include faulty hoses, water pump failure, and/or water temp. sensor failure.

Hope this helps.