A little history before I begin. I had removed the AC years ago when I first got my 4th gen and had been running a full size aluminum Koyo radiator with one 12" slim fan pushing air and I swear, I could probably leave the car idling for hours in horrible heat and it'd never overheat.

Forward to just recently, I have re-installed AC back into the car and it feels awesome! But as in most cases, overheating has become an issue now in stop & go traffic in 100 degree heat. I have the same Koyo radiator with the 12" slim fan mounted behind the radiator now, pulling air along with a 10" slim fan doing the same for the AC/condenser.

I have no leaks, fans kick on as they should, no blown fuses and everything mechanically and electronically to my understanding is working as it should. I'm just stumped. Aftermarket eBay slim fans too small? Or what? Bugs the hell out of me. Suggestions? Thanks.

One other thing. It is unusually too hot when you pop the hood open under there. I do not do any type of spirited driving and before the duhs, it's a motor, it gets hot. Before the AC I could pop the hood open after driving and go to work in there. Now, that sucker has to cool down for a good hour before you attempt to poke your nose around. Call me crazy.

 

Are you sure the fans are blowing in the right direction? Are the fans bi-directional or are they only for pushing or only for pulling? The blade design will be different between the two and I can see it not working properly if they are mounted in the wrong direction.

 

Check your radiator hose temps, if the upper is a lot hotter than the lower, replace your thermostat.

 

If the overheating problem occurs during stop&go but not during highway cruising you are probably looking at an airflow problem; fans just can't move enough CFM. Do you have a turbo and strapped for space? If not, I would suggest coming up with a shrouded fan setup. You might also ask yourself if you really need a 53mm core all aluminum koyo. Do you do road racing? I only ask b/c I have a 320whp h23 that I daily drive; stock radiator and AC blows ice cold; datalogs show the ECT never gets above 195. I would imagine I might run into a problem if I were continually boosting for an extended period of time but you can't really do that on public streets.

The stock shrouded fans made by Honda generally out perform any after market fan because of the shrouding.

 

No turbo, completely stock. Back when I bought the Koyo, I did have intentions to turbo it. I did suspect the fans as the issue and bought a set of factory fans a while back and of course, they don't bolt on. I'll probably end up purchasing a factory replacement to make use of the OEM fans and sell the Koyo.

 

As already asked, does it overheat when you're moving at a fair speed (40+ MPH)? If so, it's not an airflow problem, and I'd suspect the thermostat.

I don't run any fans on my Fluidyne radiator on my track car, and I have no cooling problems whatsoever, even running a 45 minute track session at TWS in 105F+ ambient temps. You can see the thermostat opening and closing in the datalogs as the temp fluctuates around 180F to 200F.

 

Nope, it doesn't overheat if I'm moving. A good example of when it will overheat is if I leave the house, drive through the neighborhood, hop on the freeway, exit and then grab a bite to eat in a drive-thru - guaranteed to overheat if I'm sitting there with the AC on in Texas heat. Both hoses are hot and I'm using an OEM thermostat with the blades mounted in pull style.

With the Koyo and shroudless eBay slim style fans, I do have quite a bit of "hot spot" realstate around the fans. Which I assume is causing a cooling issue. Another possibility, perhaps the thermostat is only partially opening, not allowing enough coolant to pass. I'm going to try a new thermostat and flush and report back before I replace the radiator for an OEM style w/ OEM fans.

 

Sounds like the problem is likely the fans or the t-stat since it happens only at low speeds or sitting still. Definitely doesn't sound like a water flow issue (i.e. blockage).

 

Ill ask this again, only because Ive seen it before. Are your fans Bi-Directional or are they push only type of fans? If they were designed as push only and you try to make them puller type fans instead they wont flow the same CFM because the fan blades were built at a different angle. Dont get to involved in all this. Your problem started after you moved your fan so start from there.

 

Bi-directional. Removed the bolt to flip the blade around.

 

I have a Koyo half rad with an aftermarket push slim fan.

I run warm, ~200 degrees, but I don't overheat, and I'm turbo.