93 honda civic dx

The other day, after a two hour drive, I get in my car the next day and about ten minutes after driving through the city I look at the temp gauge and its in the red. I pull over, a bit of steam floats out of the hood.

There is a crack, about 4 inches across the top of the radiator where the steam is coming out of. I figure I must have lost pressure because of it, I tried sealing it to no avail.

There's no ping or knocking, but the engine seems to be idling very high, occasionally dropping to nearly nothing for a second when I hit the clutch. My first instinct, knowing little about the problem, is to just replace the radiator, but I worry about what would have caused it to crack in the first place. I have noticed that the coolant has been slowly leaking for the past month, so that points me in that direction (I might have let it go too dry), but what could be causing the engine to idle so high? I've heard stories about blown head gaskets, but the engine seems to run well, powerfully, and consistently aside from it edling high.

I'm clueless about cooling systems. Any advice? Thanks.

 

If your head gasket is blown at a point into the header, you won't notice much of a change in power, and your oil could be fine as the coolant will leak into the header and not the block.

New radiator and a compression test should tell you.

Have you ever cleaned your IACV?

 

if its a plastic radiator, they sometimes come apart at the top like you descriped.
you should replace it because radiators need to hold pressure.
I got an all metal one at autozone.
drive as little as possible until it's fixed!