Radiator Problems on Honda Civic


I live in Colorado. Two part question -

[1] This winter I

noticed that the radiator would

spray / eject fluid out of an area

near the cap / reservoir, especially

after an overnight freeze. I can’t

find the leak but it always happened

after I drove the car around a bit.

i.e. it did not happen if the car

was stationary. I tried revving the

engine, etc - nothing.

[2] Now in the summer I am noticing

that the fluid level in the radiator

drops, the coolant reservoir gets

filled by a backflush, and the engine


Any suggestions? THANKS MUCH FELLOW

CT Folks


Well I would guess the first thing to do is to find that leak. Since you don’t seem to be able to find it, then it is time to bring in a local professional who likely will pressure test it. Keep in mind it may have an a head gasket or other issue.

Winter or summer, it is a poor idea to hold off on this kind of problem as it will never become less expensive and can become a lot more expensive very quickly.


The oil is always clean and no sign of steamy
exhaust. This seems like it is the radiator -
a two year old Modine but has quite a lot of
moldy like “stuff” at least as far as I can see
after removing the rad cap.


Most likely a bad radiator cap. The cap regulates the pressure within the cooling system, and excess pressure is released into the overflow bottle. However, if the cap goes bad, it will release pressure (and coolant) at lower and lower pressures than originally designed, resulting in fluid loss and overheating.

It could also mean a leaking head gasket, that is sending combustion gasses into the cooling system and over-pressurizing the system, but, then, you’d acutally see bubbles streaming through the overflow bottle. But, i felt I needed to tell you.


Is this two year old Modine an all copper and brass radiator or a plastic and aluminum one like the original? If its not like the original, I’d recommend that you replace it with a plastic and aluminum OEM radiator post haste.


It is painted black and appears to have plastic
tanks; perhaps and Al body. I really don’t see
any coolant leaks. Just a lot of “rust” in the


I should mention I picked up some Prestone
Radiator Clean and will try this first to
see if I can get the liquid to flow freely.
I’m also thinking of putting a T-joint
in the heater core path to flush the system out.
These will be my first try at a remedy.