Radium Coolant Tank Install (FK8)

Having a plastic coolant expansion tank in your track-focused car (most makes or models) is pretty much like having a ticking time bomb under the hood. It’s perfect for those casual drivers whose wildest journey is the thrilling commute from home to the office. But in the extreme conditions experienced on track, that plastic tank is just minutes away from failure. This is because plastic is less temperature-resistant and can become brittle and crack at high temperatures that one would experience on track, especially when the cooling system has a tremendous amount of pressure built up in it. Because of the FK8/FL5/DE5 two-piece design, this pressure can help encourage the separation at the seams of the plastic tank, leaving us more prone to catastrophe.

So, if the plastic is that bad, why do car manufacturers sell cars with plastic ones? Well, mainly because plastic is cheaper and lighter but also because metal/aluminum tanks can corrode over time, especially if the coolant isn’t maintained properly. This adds another layer of complexity for everyday drivers who might not be as meticulous with maintenance. Another reason is that the average person owns a car for roughly 6-7 years, and plastic tanks don’t usually start failing on daily drivers until about that time.

For the past three years, I’ve been pushing my FK8 hard on track days, and let’s just say, the stock plastic coolant expansion tank has always had me a little nervous. Here’s the thing: Because the FK8s are notorious for these tanks failing under rigorous conditions, and with some models now reaching eight years old, even daily drivers should be concerned.

The culprit? Heat cycles. Over time, those repeated thermal expansions and contractions wreak havoc on the plastic, making it brittle and prone to cracking. This could lead to a coolant leak at best, and a potentially catastrophic engine overheat at worst. Not exactly ideal when you’re chasing lap times or simply merging onto the highway.

The good news is there’s a simple solution: aftermarket metal/aluminum coolant tanks. These offer significantly improved durability and peace of mind. It’s a small investment that translates to major confidence behind the wheel.

So, whether you’re a seasoned track master or just a daily driver with an aging FK8, consider swapping out that plastic time bomb for a metal/aluminum upgrade. It’s a preventative measure that could save you from a roadside breakdown or calamity at the track.

Back in 2021, I became a new FK8 owner, and I initially dismissed concerns about the plastic coolant tank so I could allocate funds elsewhere into the car. Fresh off the showroom floor, it felt invincible, and I was convinced it would not fail so quickly. But after a few exhilarating track days, I realized I was living on borrowed time, and worry began to set in. The stories and testimonials from fellow enthusiasts about plastic tank failures under extreme conditions were hard to ignore. It was a very real issue and honestly more common than not on our chassis.

After three years of pushing my FK8 hard on the track, I finally succumbed to the nagging voice of reason and decided to upgrade from the plastic coolant tank in my FK8. While I thankfully dodged a bullet with the OEM unit, the gamble became less appealing as the miles climbed and the heat cycles piled on. With the car aging and countless heat cycles under its belt, the risk of a leak or, worse, a devastating failure, became too much to ignore.

Consider this a “do as I say, not as I did” scenario. While I, thankfully, haven’t experienced any issues with the stock tank, it’s not a gamble I’d recommend. Frequent track use, high mileage, or simply an aging FK8 are all reasons to prioritize this upgrade. Let this be a cautionary tale – a simple preventative measure can save you from a major headache down the road, and keep your beloved Type R on the track where it belongs. Don’t risk it like I did!

My recent 41st birthday marked more than just another year older. It was a personal turning point, a time to acknowledge the value of preventative maintenance. While some might celebrate with cake and candles, this year, my wish list included a Radium Coolant Tank for my trusty FK8. It wasn’t the most glamorous present, but it signified a newfound appreciation for reliability and long-term performance. Imagine my delight when, amidst the birthday cards, sat a single, perfectly sized gift box. The telltale weight and dimensions hinted at its contents – could it be the Radium tank I so desired?

With eager hands, I unwrapped the gift, my anticipation building with every rip of the paper. And there it was, the prize I’d been hoping for: the Radium 20-0827 Coolant Tank Kit! Normally, I’d be sprinting to the garage to start the installation, but a crazy work schedule sidelined those plans for a few days. But that wasn’t going to stop me from at least taking it out of the box and marveling at it.

I cut the tape on the box, opened the flap, and began sifting through all the packing paper stuffed inside, searching for every last baggie of parts to complete the kit. Fittings, clamps, bolts, screws, hoses, a bracket, and lastly the two halves that made up the coolant tank. My excitement quickly turned to confusion… Wait… why are there two bottom halves? Knowing the answer, I optimistically checked the box again, hoping that maybe I received an extra bottom half and potentially there was still the top half inside.

There wasn’t… What a birthday surprise! Sure enough, they sent me two bottoms and no top. I suppose the Radium employee who was packing boxes that day was more interested in TikToking than ensuring I had the correct pieces in my box.

On a lighter note, it was only a minor mix-up. I wasn’t planning on installing it immediately (thankfully!), so it wasn’t too big a deal. The next day, Angie contacted the vendor she purchased it through, who promptly forwarded the information to Radium. To their credit, they were very accommodating and quickly shipped out the missing top half.

Below you can see the correct top half now in my possession which had arrived a few days later and the “extra” bottom half off to the right standing up vertically.

Here is what the kit should have looked like when I opened it on the night of my birthday.

Radium quickly came to the rescue and sent the missing top half right away. The only catch? I had to return the extra bottom they accidentally included. It made me wonder if there was someone out there with the opposite problem – a box full of tops and no bottoms! Maybe they needed me to ship back the extra bottom to ensure balance was restored to the universe.

It was a bit surprising that Radium wanted the extra bottom piece back, but honestly, what use did I have for it anyway? Luckily, they made the return process a breeze by including a pre-paid shipping label. One quick trip to the UPS store later, and balance was restored.

Since I had to return one, I carefully selected the better of the two. Upon closely examining every inch of both bottom pieces, I found no notable defects, aside from a minor scratch. Strangely, both bottoms featured the identical nick/scratch in the very same spot, as depicted in the picture below.

The photo below has been significantly edited to make the nick/scratch more visible. It’s quite strange, but it seems likely that it resulted from the clamp holding the aluminum block while the CNC machine was shaping the design.

The sincere handwritten note to help me forgive them for ruining my birthday present.

Let’s move on from the issue of the missing top piece and dive into the installation. I know that Radium offers a PDF manual for this process, which might make my instructions seem unnecessary. However, I will cover some specific details that Radium may prefer to keep undisclosed or not explain thoroughly enough.

First and foremost, there are some rumblings throughout the community that claim the Radium tank leaks. I can neither confirm nor deny this since, as I write this, I’ve only got a couple of hundred miles on mine. I did take a few extra measures to help prevent any sort of leaks from forming over time, and I will go over these in my installation process below.

While a few companies have designs in the works (Wunderladen Racing, and PRL), currently there aren’t many coolant tank options for our cars. I opted for the Radium one for several reasons. First, I prefer to avoid Mishimoto products altogether. Second, the Radium tank’s design incorporates a swirl pot feature, which helps to separate air bubbles from the coolant through centrifugal force. This improves the system’s efficiency by preventing air from accumulating in areas where it can impede heat transfer. Third, the coolant level indicator is very easy to read, and lastly, Radium has a well-deserved reputation for making high-quality automotive parts.

My installation process:

To begin, Radium suggests using thread sealant with PTFE when installing the two elbow fittings shown below. These are both tapered-fit pipe threads and can be a bit scary to tighten since they requires so much force after only one full rotation. However, Radium notes that each fitting comes pre-impregnated with Teflon so no additional lubrication is required (besides the thread sealant with PTFE). They also state that you need to add an additional 1.5 to 3 turns until each one faces directly downwards.

It’s important to note that installing any aftermarket coolant tank, including the Radium one, can introduce the potential for leaks if not done correctly. This is just the first part of the installation process we come across that can introduce some operator error. There will be a few more that I point out further along in the process as well.

Two things quickly come to mind for me here that could lead to leaks.

  1. Not fully cinching down the tapered pipe thread can lead to leaks due to the threads not being properly seated. Male and female tapered pipe threads create a tighter seal as they are screwed together due to the wedge effect. However, to ensure a completely leak-free connection, a sealant is still recommended. These sealants fill any microscopic gaps between the threads, preventing fluids or gases from traveling along the path created by the thread spiral.
  2. Some who assemble their tank might not be using the suggested “thread sealant with PTFE” The real magic is the PTFE or (Polytetrafluoroethylene) which is chemically inert and provides superior leak prevention.

My second leak prevention measure was to go a step beyond the supplied gasket. I also applied a thin layer of Hondabond to both surfaces before assembling the coolant tank, ensuring a secure seal.

As you can see below, I have applied a thin layer of Hondabond to both halves and I will be sandwiching the supplied gasket between both halves as well.

Let the Hondabond cure for about 60 seconds according to Honda’s instructions. Then, place the gasket on one half and carefully place the other half on top. It’s important to work relatively quickly to ensure the Hondabond remains tacky and facilitates a good seal. Avoid fully cured Hondabond as it may prevent proper adhesion. Hondabond will generally set within an hour and take a full 13-16 hours for a “full cure.”

With the Hondabond applied, the gasket in place and the two halves mated, quickly move on to installing the seven hex head bolts that clamp together the two halves. It is recommended to use anti-seize on the threads to prevent galling. Tighten all screws evenly until snug in a crisscross sequence, then torque to 53 in-lbs (6 Nm). INCH POUNDS, NOT FOOT LBS

What is thread galling you ask?

Galling is a type of wear caused by friction, not abrasion (chafing). It occurs when two metal surfaces rub together under pressure with insufficient lubrication. As friction increases, the heat and pressure can cause the surfaces to adhere and tear at the microscopic level. This results in tiny transfers of material between the two surfaces. If these conditions persist, the amount of material transfer increases, creating a rough and uneven surface. In extreme cases, these transfers can become so significant that the metals cold weld together, essentially fusing them. Once galling starts, the transferred material can accumulate as lumps or balls, leading to performance problems.

There are two main reasons why following Radium’s recommendation to use anti-seize is important.

  • First, it helps ensure even clamping force across all seven hex bolts. Without anti-seize, friction between the threads can cause uneven tightening, potentially leading to leaks.
  • Second, anti-seize reduces friction during tightening, which can prevent false torque readings. When threads gall due to a lack of lubrication, the torque wrench might indicate proper tightness, even though the actual clamping force on the bolts is uneven or insufficient.

This is a bit of a stretch, but it is possible and could be the culprit for some of those who experience leaks or coolant weep. Especially if they are assembling them with impact guns, or cordless ratchets without any sort of lubrication.

Don’t forget to install the clear coolant level tube before completely joining the two halves. If you do forget, there is no way to get it in without undoing all the hard work you just went through to ensure it is leak-proof.

Lastly, it’s worth mentioning, that I didn’t wait the 10+ hours for the Hondabond to fully cure before adding coolant. But I did completely assemble the whole Radium tank, then let it sit for a few hours as I removed the OEM plastic tank and ran a few errands. All in all, it was at least 4 hours before I added coolant to it.

Assembly absolutely requires a torque wrench for those long, thin hex head bolts. Their slender design makes them highly susceptible to snapping under excessive torque, and under-torquing can lead to leaks or weeping of coolant. Using the manufacturer’s recommended torque specifications will ensure a secure joint without risking bolt failure.

Because the required torque specification of these bolts was 53 in-lbs, I made sure to get a torque wrench with a minimum rating of 10 in-lbs instead of the more common 50 in-lbs. This is because every torque wrench operates within a given accuracy range, such as ±2-4% over 20% to 100% of full-scale. Most decent wrenches are guaranteed accurate between 20% and 100% of full-scale. For example, don’t use a 30 to 250 in-lbs wrench to torque a 35 in-lbs bolt, as the wrench is only accurate from 50 to 250 in-lbs. Instead, use a 10 to 150 in-lbs wrench which will be accurate at 35 in-lbs.

Not properly torquing to spec could potentially lead to leaks and/or weeping where the two halves join. This is also another reason why some might be experiencing leaks or weeps.

Once you have completed the joining of the two halves, and not forgetting to install the clear tube for coolant level indication, the next step in the process is to install the coolant tank neck. Do not forget to include the rubber O-ring to allow for a complete seal when the coolant tank neck is mated to the tank itself. It is also a good idea to use some Loctite to ensure the X3 bolts that secure it don’t loosen up over time and potentially create a leak.

I opted not to use any Hondabond on the rubber O-ring because if I do develop a leak where this neck joins the tank, it would be very easy to remove and reseal with some Hondabond after it is all installed in the car. But, if you feel more comfortable adding a small amount of Hondabond around the rubber O-ring to help further prevent any leaking please be my guest, there is no downside to it.

Install the -10 AN plug fitting into the bottom port shown below. Be sure to pre lubricate the O-ring.

There are two main reasons why pre-lubricating the O-ring is important:

  1. Easier Assembly: Lubrication reduces friction between the O-ring and the fitting surfaces. This allows the O-ring to slide into place more easily, minimizing the risk of pinching, twisting, or damaging it during installation. A damaged O-ring won’t create a proper seal.
  2. Better Seal: A thin layer of lubricant can help the O-ring conform better to the sealing surfaces within the fitting. This creates a tighter seal and reduces the chance of leaks.

Here’s an analogy: Imagine trying to squeeze a dry rubber band around a bumpy surface. It would be difficult to get a good seal. But if you lubricated the rubber band first, it would slide into place easier and conform better to the bumps, creating a tighter seal.

I would bet that some who complain about leaks in their Radium coolant tank haven’t properly pre-lubricated the O-ring during assembly.

Even though not necessary… For complete peace of mind, I not only pre-lubricated the O-ring but also used thread sealant with PTFE on the threads of the -10AN plug during assembly. While the O-ring is the primary seal, thread sealant adds an extra layer of security guarding against any sort of potential leak.

Next, I installed the -10 ORB AN fitting. I practiced the same methods as mentioned above about using the thread sealant with PTFE and ensuring the O-ring is lubricated.

Then, to ensure a leak-free connection, pre-lubricate the O-ring on the barbed swiveling fitting before carefully installing it into the 6AN ORB upper left port of the coolant tank. Again, I used a small amount of thread sealant with PTFE just for peace of mind.

Then, install and tighten the -8AN PushLok hose end onto the banjo fitting, as shown below (bottom right). Because this is an AN fitting, there is no need for sealant or pre-lubing of anything. The sealing magic happens at the meeting point of the male and female AN fitting. These fittings have machined surfaces with specific angles (typically a 37-degree angle for the male and a complementary angle for the female). When tightened, these angled surfaces create a tight metal-to-metal contact, forming a very effective seal.

Lastly, the bracket can now be bolted on. Again, make sure to use Loctite to ensure the tank doesn’t come loose from the bracket after a few thousand miles of vibrations.

Another view of the whole thing completely assembled.

Now with it all assembled and to ensure proper curing of all sealants and Hondabond, as previously mentioned, I turned to the disassembly and removal of the OEM plastic coolant expansion tank.

Here we begin with what it recently looked like in my engine bay.

Start by disconnecting the expansion tank inlet hose. Use a 1/4 inch extension to plug the hose preventing anything from leaking out.

Next, there are X2 10mm bolts that need to be removed.



Then, using a 14mm socket, begin to unbolt the engine mount bracket. There are two 14mm bolts securing the bracket. This one is easy to access; the other, as you’ll see below, is a bit more challenging to access.

To gain access to the second 14mm bolt, you will need to unbolt the A/C suction hose clamp by removing the X1 10mm bolt as illustrated below.

Carefully twist the bracket up to allow access to the hidden 14mm bolt.

Unfortunately, you won’t be able to use a socket for this as there isn’t much clearance. You will have to use the closed end of a 14mm combination wrench (or a similar tool, such as a ratcheting wrench or box wrench) because those have a low profile; you will be able to sneak it in there.

With both 14mm bolts removed, now the bracket can be removed.

By removing the bracket, this now allows you to lift the coolant tank up, gaining you access to the expansion tank outlet hose clamp.

Using some pliers to squeeze the clamp which releases the tension from it, slide the clamp away from the outlet nipple.

With the clamp slid away from the nipple, you can now pull the expansion tank outlet hose off the expansion tank. But make sure to keep the nipple pointed upwards as this will prevent any coolant from spilling. You will be reusing all the coolant from the OEM tank to fill the Radium one.

The OEM tank should now easily come out.

There is a rubber cushion that the OEM tank sets into, which might add some resistance when trying to remove the tank. Just ensure you are pulling directly upward when trying to remove the tank and you should have no issue. You can see the rubber cushion I speak of in the picture below.

Next, there are two 10mm bolts that secure the expansion tank bracket to the chassis strut area. They will both need to be removed, allowing you to completely remove the bracket. This bracket will not be used in conjunction with the Radium tank, so you can throw it away or store it somewhere in case you ever want to return to stock. Make sure to save the 10mm bolts, though, you will be utilizing them when installing the Radium tank.

The first of the X2 10mm bolts is easily accessible.

But the second one will require a bit more finesse when trying to remove it. Make sure you watch out for the ol’ freedom solenoid (AKA Spool valve assembly, more commonly known as the VTEC Solenoid.) Damaging this or any of its connections will basically turn your Type R into a Base model Civic.

I had to use a small 1/4 inch ratchet to access and remove the second 10mm bolt.

Then you can remove the second expansion tank bracket by unbolting the two 10mm bolts as indicated below. Make sure to save one of the 10mm bolts from this one too because again, you will be using it to install the Radium tank.

Remove the bracket completely as it will also no longer be needed either.

Now that the coolant tank and all of its brackets are removed, take this chance to thoroughly clean the previously inaccessible area underneath. Use a microfiber towel dampened with WD-40 to remove any accumulated dirt and debris.

Now you can test fit the Radium tank. The only way I was able to tighten down the 10mm bolt in this location was by using a looong 1/4-inch swivel extension and a shallow 1/4-inch 10mm socket. Then there are the other two bolts on the side of the chassis near the VTEC solenoid that need to be bolted in. I just used a 1/4-inch ratchet with a combination of both deep and shallow 10mm sockets, no extensions.

Just to be clear, there are three points at which the radium bracket bolts to the chassis. Again, you will be reusing the 10mm bolts you removed from the OEM brackets to secure the Radium bracket.

(see the picture below of the looong extension)

But first, we need to address some issues that I came across during the installation of the Radium tank.

One, as you can see below in this overly edited photo that spotlights the Radium tank bracket making contact with the aluminum part of the A/C suction hose. Mine was making full-on contact and to me, I just thought that after months/years of chafing, eventually a hole would be made in the aluminum A/C line. This would in turn cause all the freon to leak out and stop the A/C from blowing cold.

As you can see below I have marked the bracket where the A/C line was making contact. My solution was to remove the whole tank and bracket, then using a flappy wheel on a grinder I would grind away some of the bracket allowing for more clearance of the A/C line.

The second area of concern was the proximity of the expansion tank outlet hose to the engine mount. Over time, the constant contact between the rubber hose and the aluminum mount could potentially wear a hole in the hose and cause a major coolant leak.

Again, I marked the area of concern and was going to grind away a bit of the aluminum motor mount to allow for more clearance between the two. You may be thinking that because the fitting that the hose connects to is a swivel, I could simply twist the hose slightly to gain some added clearance. However, there is a large wiring harness that is routed right underneath the expansion tank outlet hose, which makes it difficult to swivel the hose away from the motor mount.

The third area that concerned me was the clearance between the expansion tank outlet hose and the front of the engine mount (pictured below). In my case, using a Radium CCV catch can created some tension on the hose, causing it to rub against the mount. This might not be an issue for those using a different brand of catch can or no catch can at all.

So as mentioned above, to solve the A/C line rubbing issue I was going to grind away some of the Radium bracket.



Rather than reinstalling the whole thing, I simply test-fitted the bracket on the car to ensure there was optimal clearance before complete reinstallation. As you can see, I made a much more comfortable amount of clearance.

A bit closer up. From this angle, it appears the line is still hitting the lower part of the bracket, but rest assured, it is not even close.

I bet some of you are thinking that I should have just “bent” the A/C hardline slightly which might have allowed for more clearance between the bracket and A/C line. However, because the A/C line is held in place by the suction hose clamp, and the other bracket on the chassis strut area, there isn’t really much room to bend the line away from the bracket. What you’ll most likely end up doing is causing it to rub on another area of the A/C line, Coolant Tank, or even chassis. For me, the simplest solution was to just grind down the bracket slightly.

I then pulled out the bandfile and ground off a bit of the motor mount to allow for more clearance of the outlet hose.

As you can see, I not only removed the rough casting imperfections, but I also removed about 1/4 inch of the aluminum from the mount itself. No structural integrity was or will be sacrificed in the small amount of material I removed.

Now, with the whole thing reinstalled, you can see I have a lot more clearance between the bracket and the A/C line. If, like me, you took the bracket back off the tank, make sure to reapply some Loctite to the X3 bolts that secure the bracket to the tank.

You can also see how much more clearance there is between the outlet hose and the motor mount.

I’m sure, just like the A/C line issue, there are some of you thinking that I should have just used zip ties to secure the hose away from the mount to prevent any contact. However, I dislike the look of multiple zip ties in a car’s engine bay… they look tacky. Sure, maybe one or two is okay, especially if they are somewhat hidden from plain sight. But in this instance, I opted for a cleaner solution in this highly visible area. After all, aesthetics matter in the engine bay too! Have some damn pride in your work.

I had also used the bandfile to remove some of the casting imperfections from the front side of the mount, but it was still too close for comfort, and I resorted to just taking about 1.5 inches of a rubber hose and slitting it down the middle, placing it over the outlet hose, and this allowed me to insulate the outlet hose from making contact with the forward part of the mount. (no picture of this, sorry)

Don’t worry though, I executed this tastefully so as to not contradict my statement above about aesthetics in the engine bay.

Lastly, I want to discuss the lack of space available for routing the supplied coolant tank inlet hose. Again, as you can see below, because I’m using a Radium CCV catch can, it is very tight where the coolant tank inlet hose needs to connect to the expansion tank pipe that bolts to the air inlet pipe. I have to be honest, this was probably the most frustrating part of the whole install. Be careful when routing this hose to make sure it is not making contact with the serpentine belt. If you’re not using a Radium CCV catch can, then this hose will be easy to connect.

Success! Here’s the tank completely installed, but if I’m being honest, I’m a bit disappointed that it sits a bit crooked in the engine bay. Radium’s online pictures definitely didn’t do a good job depicting this. But hey, that’s why I’m here – to expose all the little details! A heads-up for those with OCD and the desire for geometric harmony: once you see what I’m about to show you, you’ll never be able to unsee it again.

It’s true, the crookedness is subtle in head-on photos. While I’m not accusing Radium of intentionally hiding anything, the straight-on shots they provide on their site definitely minimize the effect. As you’ll see in the upcoming photos, from other angles, the misalignment becomes quite noticeable.

Below you can see what I mean about how the coolant tank doesn’t line up with the expected parallel line of the valve cover as the OEM coolant tank did.

Interestingly, the coolant tank aligns perfectly with the strut mount on the chassis. This could be the intended design reference point, rather than the valve cover. It makes sense considering, for this kit, Radium is using their universal coolant tank design. To keep costs down, they likely opted for a bracket adaptation instead of creating a bespoke tank specifically for the FK8/FL5/DE5. This way, they could utilize their existing, proven design with minimal modifications.

So, if you can just change your thought process of what you perceive as parallel, then maybe you can get accustomed to the new angle of the coolant tank.

I’m just happy they designed the radiator cap to line up the same way as it did on the OEM tank. This way, at least my Spoon radiator cap is still in perfect parallel with the valve cover.

Again, another camera angle to emphasize just how noticeably askew the tank is compared to the valve cover.

Another one from the other side of the car.

But from these angles, it all looks well.

Don’t overlook this critical step of the install process! Make sure not to route your new overflow tube into your wheel well area. This could spell disaster if you had some coolant spill out and get under your tire. I know it might be more aesthetically pleasing to have a short overflow tube, but there is just too much risk in making it short. I used the whole length supplied by Radium in the kit, and ran mine down along the chassis rail back to the firewall, routing it down and behind the steering rack. This way, if some fluid does happen to spew out, it will not get under the drive wheels of the car.

Only a couple hundred miles into my Radium coolant tank ownership and I’m already finding good ways to adapt to its unique positioning in relation to the theoretical parallel line of the valve cover. It’s an exciting challenge! But I think I’ll eventually be able to retrain my brain to accept this as the correct position.

Overall, it’s a pretty easy install, other than having to contort your hand into strange positions to access a few 10mm bolts and possibly having to grind away some aluminum to prevent any chafing or premature failure of your A/C and/or cooling system. The kit includes everything you need for installation (as long as their employees aren’t too busy TikToking). However, I highly suggest that before embarking on the install, you purchase Hondabond, thread sealant with PTFE, and a quality inch/lb torque wrench. These three items, and of course, properly lubricating the O-rings, will help ensure you have no leaks.

Protip: be mindful of not dropping your tool into the engine bay abyss like I did. When that happens, it makes me wish there wasn’t an aluminum undertray preventing all tools and hardware from falling all the way to the garage floor. If you are like me and you do end up dropping a tool or random 10mm bolt down there, you’re going to, unfortunately, have to jack up the car and remove the aluminum undertray to access that blasted 10mm wrench I…ehm, you dropped.

Another great thing about this install that makes it very easy to execute, especially for the less experienced DIYers out there, is that there is no need to re-bleed the cooling system; you can simply pour the remaining coolant from the OEM tank into the Radium tank (after installing it) and you’re good to go. Just make sure, after complete installation, to start the car, check for any leaks or weeps, and wait for the fans to kick on, which indicates that the cooling system is working properly. After the fans kick on, you may or may not need to top off the coolant tank.

Be sure to wait until the engine cools to below 100 degrees Fahrenheit before checking the coolant level in the tank. Mainly, because you don’t want to remove the coolant tank cap while it is fully pressurized, and secondly, allowing the car to completely cool will give you a more accurate read of the coolant level in the tank.

Again, just to re-address the chatter about these tanks leaking… I feel that most of the people experiencing leaks or weeps on their tank may have haphazardly assembled it, not following the guidance from Radium about using thread sealant with PTFE, pre-lubricating all O-rings on the ORB/AN fittings, and lastly not properly torquing or failing to get proper torque readings by either galling the threads from not utilizing anti-seize, using a poor quality torque wrench, or not using one at all. Let’s face it; this tank is Radium’s universal design that is used on multiple platforms out there from off-road, on-road, and race car applications. If they were really that bad and leaked, wouldn’t Radium rethink its design and fix the issue? I’m betting that OE (operator error) is the cause of many of the leaks.

If you follow the specific advice I gave about ensuring proper assembly and how to take leak prevention even one step further. I feel safe in saying that you shouldn’t encounter any leaks or weeps and that you should enjoy all the benefits and peace of mind this tank offers to us FK8/FL5/DE5 owners.

I truly hope you enjoyed reading my long-winded version of how to install the Radium Coolant Tank on your car. I know for sure every one of you reading this must have learned at least one thing. And for me, being able to help educate new enthusiasts and seasoned pros, even if it is only one small piece of knowledge, then I feel like my blog made a difference. Because we can either all just complain about the current state of car culture right now, or we can be the change. Because like Teddy says, “Complaining about a problem without posing a solution is called whining.”

As always, if you have any feedback, whether positive or negative, I’d love to hear from you! Your comments and questions are what make writing these overly comprehensive articles worthwhile. Please, feel free to leave a comment below, reach out on Instagram @Functiontheory, or shoot me an email at Billy@Functiontheory.com. Knowing what you find helpful, interesting, and relatable allows me to keep creating content that empowers car enthusiasts of all levels.


  1. Wow did not expect it’d be that much work and barely even fit. Love the look, but, both tubes rubbing, poor routing, barely supporting their own CVC catch can and strange 2-part design just prangs me out.. at least it uses AN / JIC fittings, though, can’t stand welded on push fittings!!

    Bless you for the mad detailed install with pictures, always love your posts. Big respect from UK!

    1. RIGHT?! Honestly, thought it would have fit much better and they would have thought of everything when developing the kit. I mean, I have both of their catch cans (PCV,CCV) and those are great and didn’t require any modifications when I installed them. I do wish they had thought about fitment with people utilizing their CCV catch can. But there really isn’t that much work that goes into modifying it to work flawlessly and I still maintain their stuff is much better quality than others on the market. I think they use the two piece tank because this way they are able to incorporate that swirl feature. I know it can be done without necessitating the use of a two piece tank, but i think for ease of manufacturing purposes that the best option. Thank you so much for your feedback, I love to hear from the readers!

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