F20/H22 complete cooling system upgrade civic chassis specific (nate’s car)

F20/H22 complete cooling system upgrade civic chassis specific (nate’s car)

About a year ago Nate bought his 92 F20B swapped civic SI, and since then we have been slowly fixing up what the previous owners had done poorly. Ever since he bought the car there has been small pin hole leak in the radiator. It was nothing to worry about, just would drip a couple of drops out while driving splashing coolant drops on various parts under the hood. As many of you should know, the cooling system is a sealed system and when there is a leak of any size in the system it will cause air to get in and cause cooling issues. This is because the air will actually block the passage of coolant slowing or even halting the coolant from flowing to the radiator. It can also cause false readings on your temp gauge if there is an air bubble where the temp sensor is, by not allowing the actual coolant to touch the sensor allowing it to accurately read the temp. All of these things are not good for the overall performance of your car (obviously) But believe it or not there was other major issues that we had to address before we got to actually redoing the cooling system in his car. This is why it took him a year to finally get the funds together to do the complete system overhaul, since he was doing other upgrades. As you will read below no expense was spared in completely redoing his cooling system, but this is because the plan for his car is to track it.  The trouble with redoing the cooling system is that you pretty much need to do everything at once or you will just be spending heaps of money on coolant, since every time you change one part out you will have to drain and add more coolant. So for Nate, it just seemed more sensible to just save up and do the whole thing at once, which is what I would have done too.

If you want to read the feature we did on his car 7 months ago, where we go into detail about what is done to the car, and how budget minded it is while still remaining performance oriented.  please click the link below.


So hopefully you read up on his car, and know how far he has come in the last 1.5 years with Civics.

Let’s start this article out with some pictures and a list of all the things we are redoing.


  • Mugen thermostat
  • Mugen fan switch
  • Feels radiator cap
  • Benen rad stay
  • Circuit hero cooling plate
  • HPS hoses
  • Koyo Rad (B sereis)
  • Mishimoto 12 inch fan
  • New OEM radiator rubber insulators
  • Exedy slave cylinder for B series
  • OEM TYPE 2 coolant (the best there ever was)

Since Nate has an F20B, which is essentially an H22A there is some confusion on which parts to use, when this motor or even an H22 is in a civic chassis. Below I will explain what exact parts you need to use, and what challenges you will face.

Lets address the elephant in the room…WhY dId He NoT gO fUlL sIzE? I know that’s what most of you are thinking. Yes obviously a full-size would have been the best for cooling, but those that have an F/H series civic will know that there are some major clearance issues with the way the alternator is mounted. Of course like Nate, you can get a relocation bracket for the alternator to move it lower where the A/C mounts. But after we measured out a full size in his car, there was no way it was going to fit with out some modifications. Yes you can get an alternator bracket that allows you to run a D series alternator which is a bit smaller and might allow for the clearance of the full size radiator. But another thing we noticed with the F/H series swaps is the header goes out pretty far towards the core support/radiator. Even though a full size would clear the header, it would only clear the primaries of the header by about 1 inch from the radiator and we both believed that would be too close and would cause the radiator to actually get hotter since we are talking about the primaries directly from the head before they turn down.(these can get really hot after a few laps on a track) This we thought would cause too much heat soak, by having the header actually heating up the radiator, there for canceling out the added cooling benefits of the full size. He did dabble with he idea to do a tucked full size, but after talking it over with some of our track buddies it was decided to just stay half size. Not to mention it was going to be much more expensive to run a quality tucked set up. Running a tucked set up is also more challenging to bleed unless you have a swirl tank which is pretty much a must have when running a tucked radiator. This was all extra money, and extra modifications that would take some of the reliability of the car away. Im sure someone reading this knows of someone, somewhere that is running a full sized with a F/H series, or running a tucked set up and I’m sure it works fine for them. But for us the simplicity, reliability, availability, and longevity of maintaining an OEM style set up was the best option for us. (its also worth noting that its easier to fit a full size in an EK chassis with a F/H swap than it is an EG chassis)

So hopefully you’re reading this because you have an F/H series swap and you are trying to find out the best solution for the cooling set up on your car. Let’s talk about specifics and what all of our research turned up for compatibility of parts for X motor in Y chassis.


  • Starting off with, what thermostat you should use? All JDM/USDM H22A, H23 vtec, and F20B utilize the same thermostat. so that’s what we used.
  • Now the fan switch will be a little more confusing. The 92-96 H series actually had two fan switches on one motor. The one you will be using is the fan switch for the 97 up H22A, they only had one fan switch.
  • Radiator caps come in two sizes… ones that fit all STOCK radiators on Integra 94-01, Civic 92-00, Civic 01-07, RSX 02-06, TSX 04-07, S2000 00-07, Fit 07+….. And ones that fit all stock radiators on Honda Civic/CRX 88-91, Prelude 92-96 and Integra 90-93. If you are running an aftermarket radiator (most aluminum upgrades) you will want to order a radiator cap for a Honda Civic/CRX 88-91, Prelude 92-96 and Integra 90-93  if you order one for a stock radiator on a 92-00 civic/94-01 Integra it WILL NOT fit your aftermarket radiator. so be careful when ordering.


Which radiator hoses do you use for this swap? well this could possibly be the most difficult question to answer, as there are many ways to combine different upper and lower hose combos. But since no one sells individual silicone upper, and lower hoses and he didn’t want to run OEM rubber ones. Nate decided to go with 90-93 integra LS hoses. The lower one works perfectly with no modification necessary. But the upper one requires you to trim about 2-3 inches off each side for it to work without kinking. But it does work, and it works well. Now if you don’t want silicone hoses you can just go to an auto parts store and get the lower one for an Integra LS, and an upper for a Del Sol VTEC.  or you can just cut and chop your own, orrrrr use the universal flex hose. (which is the most ghetto thing ever) Don’t let me catch you with flexible radiator hoses on your car!


We trimmed the hoses by using a hacksaw then burning the ends with a lighter to clean up all the threads, and rough edges. You could maybe use a razor blade but it might be difficult to keep the edge straight.


The benen rad stay, and circuit hero cooling plate are just for the 92-95 chassis. You would use what ever one is specific for your chassis, for example if you have an EK you would get EK specific ones.


Koyo radiator for the 92-00 civic B series, a mishimoto 12 inch “puller fan”, and that good ol TYPE 2.



Now for the final most important upgrade that will allow for all this to properly work. The slave cylinder! So, if you haven’t done a F/H2B swap and you’re still running an F/H series trans then you will come across the issue of your slave cylinder running so close to you’re radiator that you will have to run a pusher style fan. Pusher fan’s are bad for a few reason… 1, it can block up to 35% of air flow thru the radiator. 2, you will have to run a smaller 10 inch fan to get it to clear the core support/bumper bracket area. The main issue is, the OEM salve for the F/H series has a bleeder screw that comes out at a 90* heading straight into the radiator. This can be remedied by using a b series slave and wallowing out the hole closest to the bleeder screw (the hole on the right) about 1/4 inch. If you do not do this you will have to run a pusher fan, or get a b series trans. On the picture above you can see how the bleeders come out at two totally different angles, and you can see how the one hole on the left lines up perfectly and the one hole on the right is just slightly off. I was skeptical of this at first because I was afraid it would alter the throw of the rod in the slave possibly not allowing for full disengagement of the clutch and over time slowly wearing out the synchros. But after thinking about it more, one of the holes bolts up without any modification so the throw will still be the same.


Thats the complete parts list with all the specifics you’ll need to know. Let’s now dive into the actual process of swapping everything out.


so this is what it started out as.


above shows the drips from the small leak, and the dents in the radiator where the previous slave bleeder came out. It was damaged I’m guessing from previous owners bleeding the clutch and hitting the radiator with the wrench (because the bleeder screw was so close to the radiator) In the picture is the new B series slave and you can see all the room it frees up. Keep in mind that in the pictures above he still has the pusher fan mounted too.


from this angle you can see the dents in the fins where the bleeder was close to the radiator.



I’m not going to do steps, just one big long install process. However it will be in the correct order, making it easy for you to follow along.

Make sure the car is cool, drain all the coolant, pop the radiator cap off to allow for any vacuum suction to free up allowing for full evacuation of the coolant. Slide the radiator over flow up as it is just set in (no bolts to remove it) Since we are not going to re use the radiator hoses we just disconnected them at the thermostat housing (behind the distributor, and at the head directly in-front of the distributor) Push the hoses further on to break the seal then pull them off, otherwise they will act like a Chinese finger trap. disconnect the fan (should be an OEM grey connector) and lastly unbolt the rad stay. The radiator should just pull up and out of the engine bay, and now you’re engine bay should look like the picture below.



Now find the fan switch, it will be screwed into the thermostat housing. Unplug the switch connection.


Now take a 22mm wrench or deep socket and loosen the fan switch.



above is the old OEM fan switch vs the new Mugen fan switch.


Now you’re going to remove the thermostat housing. There is three bolts to remove, 1 bolt holding a ground wire on, and 2 others that actually fasten the housing to the engine.


keep in mind the orientation of the thermostat so that you put the new one in correctly.


as you can see above there is a ton of gunk built up around the housing. this must be thoroughly cleaned. We used a scotch brite pad.


Above is a good comparison between the Mugen on the left and the “autozone” one on the right, you can clearly see the differences in quality. It’s still funny to me that people don’t want to spend money on name brand quality parts when fixing up their cars. Its called fixing up, not fixing down!


Any time you ever do any thermostat install, you must remember to keep the jiggle pin on the top of the thermostat. This allows for any small amount of air that might get in the system to flow through thus not causing any over heating issues because of air trapped in the system. You must keep it up because the air bubbles will naturally go the the highest point, and if this jiggle pin is on the bottom or the side at all you will not fully be able to bleed the air out of the system, and will most likely always have overheating issues.


On the OEM thermostat or the Mugen one (which is just an improved on OEM unit) the rubber gasket will have two rubber nipples on each side of the jiggle pin that will actually fit into the thermostat housing on the engine side and will make it impossible for you to install the jiggle pin incorrectly.


Once you have fully cleaned the thermostat housing, you are now going thread in the new fan switch. Notice there is a rubber “O” ring already on the switch so it is not necessary to put any extra gasket material on it.


Fully tighten the fan switch once the housing has been completely reinstalled and tightened on the engine.


Above is the new Koyo radiator


Im not even sure if anyone actually knows the correct way to install these radiator fan zip ties? But, I do know that a lot of people say they are a bad way to install you’re fan. Personally I have never had an issue. Make sure you test fit the radiator and fan in the engine bay to check for proper clearances, incase you have to slide your fan around or mount is a little offset before you actually secure it to the radiator.


When you get a new electric fan you will almost always have to install the OEM connector from your old fan, so that it will plug into the cars wiring harness. Please also test the fan to make sure the polarities are correctly wired, so your fan will spin the correct the direction for a push or pull application. You can test the fan by unplugging the fan switch off the thermostat housing and jumping the plug on the wire harness side with a paper clip (or something similar) this will cause the fan to turn on (the ignition will have to be on, but the motor not running) also keep in mind that the fan blades are curved and cupped a certain direction for pusher and puller type. You simply can’t just reverse the polarities to make it pusher or puller, yes it will spin the opposite direction but it will not move the correct amount of air that the fan is rated for. You have to actually unbolt the fan blade from the motor and flip it over (if the fan you bought will allow for that). So please be aware when you’re ordering a fan to make sure you get the correct pusher/puller type that you desire, and make sure that you correctly wire the polarities so it spins the correct way.  Oh and I’m sure the haters out there are yelling at me for not soldering the wires… Well fuck you, this way has worked fine for me for ever on many, many, many applications!


heres the radiator back in, and you can see the lower radiator hose works just fine.


we trimmed the upper hose and got it all clamped on. We had a slight issue getting the cooling plate to fit, simply because the core support on his car is slightly pushed upwards. It had nothing to do with the quality of the cooling plate. After massaging everything, we were able to get it all to work together in unison. Pour in 1 bottle of coolant, then start the car and let it idle until the fan comes on and all the air bubbles have bubbled out of the radiator, continuing to fill the radiator with coolant until it is full and the car has fully cycled the fan and you’re confident the thermostat has opened. The best way to tell if the thermostat has opened is touch both radiator hoses, they should both be equally hot. If the lower one is cooler than the top, or vice versa then your thermostat has not opened. When installing a lower temp fan switch the fan might turn on before the thermostat opens, so just pay close attention to that.


And now for the pièce de résistance… the Feel’s Honda Twin cam radiator cap




Above you can see how important it is to make sure you are using a B series clutch slave. with the puller fan on its a tight squeeze. Having a puller is much better than a pusher just think about all that plastic from the fan that is blocking the radiator as you are driving down the freeway not allowing the most amount of air possible to flow thru the radiator.


the picture above shows how good the upper radiator hose fits after we trimmed it down.

And here is the final picture of the completed project.


Thanks for taking the time to read this article! I think it’s a very important write up for people who actually have these swaps in their Civics and are looking to properly upgrade their cooling system. This article will help dispel any rumors, or myths about what parts can or can’t be used. All these parts 100% fit, and nothing requires any modifications expect the upper radiator hose, which is super easy.  Plus doing this doesn’t require any chassis/body modification, therefore making everything easy to install and will be reliable because you are using factory locations for everything. Currently its 100 degrees in Vegas and his car is performing flawlessly.

As with all my write ups… If you have any questions please don’t hesitate to reach out to me via: email Billy@functiontheory.com, instagram @functiontheory, or just comment on this post. I truly want to help in any way possible. Also the only way to help everyone see this who needs to see this is by sharing, liking, or commenting.

Thanks again, and have a wonderful weekend. Hopefully I have motivated you to get out and work on your car!




2 thoughts on “F20/H22 complete cooling system upgrade civic chassis specific (nate’s car)

  1. Yeah I have an F22B in my EK civic & the H22 slave cylinder issue, you have to be creative for sure. I ended up running a half rad with a pusher fan, no shroud because it wouldn’t fit & there were two piece of the plastic guard in the fan I had to snip so that the H series bleeder valve has room.
    I learned this on my own then read about how a few guys did this on honda-tech. Theirs plus mine have been working flawlessly.
    I have wondered what benefits would be from doing a full rad but when I read that it would be safe to run a half rad, so I just stuck with it.
    I’m not sure what ECU he is running but if he has Hondata he can actually go in to the misc. parameters & put a lower temperature for the fans to come on. I have tuned two of my cars this way & my friend’s cars. We have had great results & it offers the benefit of relief knowing your fans will kick on sooner than stock.
    Great articles man, I enjoy reading your stuff.

    1. Thanks man I appreciate the kind words. Yea he is just running a stock ecu, so he can’t change the fan temp parameters. That’s a little out of his price range right now. Plus I feel that the pusher style will block too much air flow, which is why we switched it. Yes a pusher works well for street/spirited driving, and drag racing. I’m still skeptical about it when actually on a track doing multiple laps. Honestly if we could have fit a full size then we would have but that dang alternator made it to challenging.

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