My ED6 overheats on hot summer track days at a low speed track. But that's only after 15 hard laps. So I wasn't inclined to fix this problem. But then the odor of coolant kept wafting through the car cabin, so I popped the hood and saw this:

Leaking fissures in the plastic, not good one week before two track days!
Note: the B-series hose is a little large for the D-series radiator.

After some researching on hybrids.jp and honda-tech.com, I concluded a DA (90-93 Integra) radiator is the best solution for the dollar. Eventually I may upgrade to a Koyo Aluminum or Fluidyne, but these are very expensive. Going with a generic/aftermarket unit will only cost $100 or so. Upgrading to DX/Si radiator is another option, but the DA is the same price and more capacity! And it's sized correctly for a B-series engine.

Modine has one of the best reputations in the aftermarket sector. This radiator came with block off plugs for the AT coolant feed. It also included bolts/nuts to mount the No. 1 fan, it's design disallows the reuse of the Honda 10mm bolts.

But where to buy one? Quite a few Internet suppliers can deliver radiators quickly. I lucked out and sourced mine locally. I got a unit manufactured by Modine. They have a great reputation amongst the aftermarket OEM-style manufacturers.

Some comparison shots of the Std. radiator versus the DA radiator. Thicker and wider! NOTE: It will place the fans much closer to the engine! Make sure you have enough clearance!

WARNING! In my experience, Honda has two radiator/fan combinations in 88-91 Civic/CRX. The fan shroud may have a different mounting style, so you may need to modify or get a different fan depending on your car. I got lucky and my fan worked with the 90-93 radiator.

1. Drain the radiator. Wear eye protection! Coolant splash can easily get into your eye! This is bad!  
    
2. Disconnect the upper radiator hose.  
    
3. Remove the upper two radiator mounting brackets. I recommend buying new ones. The bushings in it are to absorb shock on the radiator. Also, the driver's side is different on the Std. Civic, so you will need a DX/Si bracket. Don't forget to transfer over the coolant hose plastic clip.  
    
4. If there are any AC line brackets in the way, it's probably a good idea to remove or loosen them.  
    
5. Remove the No. 1 fan (two 10mm bolts on top, and disconnect the electrical connector) I believe I had to go underneath the front crossmember to get access to this connector. Once it's unhooked, just pull it straight up and out. Pay attention to see if the fan shroud has it's rubber locating bushings on the bottom still. Sometimes they fall out during removal.
   
   Now is a good time to test fit the fan on the DA radiator. Make sure your fan is compatible!  
    
6. Remove the No. 2 fan -- the most difficult part of the job. First remove disconnect the electrical connector and detach the AC line mounting bracket. Look around carefully, it maybe a little hard to do, so you may need to pull up on the fan a little in order to access a 10mm bolt. There is another wire mounted on the shroud you may need to disconnect as well.  
    
7. You should have clear access to the lower radiator hose. Disconnect it.  
    
8. Remove the radiator.

Pretty much the reverse of removal. Some important notes:

• Make sure the lower radiator bushings are in place when installing the new radiator.  
   
• Don't bend the new radiator fins when installing.
  Be careful! You may want to use some cardboard to protect it during install.  
   
• Don't forget about the fan shroud's locating bushings! Make sure they don't fall out accidentally during reinstallation.  
   
• I installed the No. 1 fan by forcing the top mounts under the radiator's mounting tabs. This allowed the shroud to sit a little more flush on the radiator and be further away from the engine. It's a tight fit!  
   
• I plan on removing my AC. So I didn't reinstall the No. 2 fan. If you put it back in, it maybe a tight fit! Beware!  
   
• Do not overtighten the bleeder valve when topping off your coolant!  
   
• Keep an eye on your car for a week or two.
  Make sure there are no leaks!