Dude, you guys just saved me. Was having an issue with my overflow filling to the brim with coolant, and my car then overheating. Everything I was reading was saying head gasket. I watched this video just on a whim, and it made me realize, I actually had my caps swapped. Yall are the best.

Hi Jon, I hope this solves your cooling problem and thanks for the plug. My solution on our sprint/endurance cars is to simply use the stock/oem caps as Subaru intended, no aftermarket caps to fiddle around with. If you don't get the caps right you can spend a ginormous amount of time and effort trying fix an overheating issue. Putting the caps on correctly may not solve the overheating, it could be something else, but you have to eliminate that variable first. Next, what we've found is most important is proper ducting into the radiator and sealing it all around the edges so the airflow cannot slip past it. A vented hood makes a big difference too. If you watched our KZfaq video on the last Cascade Enduro you heard me say that after 6 hours of racing our coolant temps were still slightly below normal on the OEM gauge. Later our datalogger confirmed our temps. And for your audience, the rule of thumb so you don't get the caps swapped backwards: The cap with "ears" goes on the expansion tank because Subaru wants you to open that one to fill/check the coolant. The round cap without ears goes on the radiator because Subaru doesn't want you to take it off, so they make it harder to grip it.

I've ran Mishimoto radiators on a few cars now and I must say that using OEM caps are the way to go. I always had overheating issues when running anything aftermarket. Go OEM and in the proper location, you'll be good to go!

Great video as always guys 👌 I’ve tried to explain this so many times to friends in the Subaru community but now you’ve done the perfect video explaining it all, I can share the link with them. Another pointer not covered is the reduction in size of the overflow tank usually when fitting front mount intercoolers, this can cause issues whereby the coolant overflows the overflow tanks capacity and then when the two way cap draws back when cooling down, it empties the smaller capacity overflow tank and draws air which then causes the air pockets in the system and head gasket failure. Keep up the great vids guys 🤘

The reason for the expansion tank is that due to the location of the turbo charger on dual cap cars, the cap on the radiator is no longer at the highest point of the system. In order for the system to function properly, the fill point must be at the highest point in the system (just like how a brake bleeder must be at the top of a caliper). Notice how the 2010-2012 Legacy GT did not have an expansion tank because it has a bottom mount turbo.

I've seen a lot of folks ditch the expansion tank for track use. My car, which is basically one giant experiment, is actually running an N/A radiator + JDM crossover pipe without the expansion tank and only one radiator fan with the USDM EJ205. Coolant temps have stayed below 200 on the track so far. Ill find out how it does with the new turbo tomorrow :)

I'm surprised you guys didn't already know this. I have been trying to tell people this for years!

So it wasn't the head gaskets, didn't someone say it wasn't?...😀 I'm just glad you got it figured out.

The Subaru cooling system can be a right pain at times if you don't know the difference between the expansion cap and the radiator cap, however it's made worse by companies listing all the caps as rad caps.. 1 way valve on the radiator, 2 way on the header.. Very Interesting video for people with coolant issues being led to believe it's hg failure 👍

Hi guys , great video , I do a lot of track work in my Impreza and I’m a plumber by trade so My understanding of the way the caps work is that both caps lift sending expanding coolant in to the expansion tank (at different pressures) but only the header tank cap draws the coolant back as that is the highest point of the system. If you ever noticed when the engine is cold , say it was left over night the coolant level is never right to top and there is an air gap and once the system pressurises again this air gets pushed out and the cycle of push/pull continues. If you have the 2 way cap on the radiator you may get air pockets forming and this is a lower point in the system hence the overheating. I could be wrong but it is may understanding of it. A friend with a s204 had this happen at the Nürburgring and a head gasket failure shortly afterwards. Caps were fitted incorrectly.

So happy to actually see or find a very concise video about this topic as I and apparently many many others had absolutely no clue about this one way & two way valved cap my OEM radiator on my 2012 WRX finally let go at the crimped plastic endtanks and started leaking. Swapped out for a koyo rad radiator and radiator hoses so it obviously came with their cap and upon install was when I started to find out about all this one way two-way valve craziness and obviously when I started searching online trying to find out why and where to put the higher pressure cap where to put the two-way valve and if it was even worth using one of the higher rated pressure caps. I most definitely did see very erratic coolant temps and it would get over 208 and rather quickly once I understood what was going on and had the correct pressure caps in the right locations everything's calmed down and worked out wonderfully and when I pull my car in the garage and shut it off you can actually hear that vacuum and you can hear the system sucking the coolant back out of the overflow which kind of tripped me out at first until I realized what was going on and that that was actually correct but thank you very much for the content in this video it was wonderful also very excited to hear what else you find out with continued testing on this topic.

I’ve ran dual 2-way caps for a couple years of track days now. 1.3 bar ARC cap on the expansion tank and 1.4 bar CSF cap on my radiator. I think the important part is to have a 2-way cap on the expansion tank, and the pressure relief on the expansion tank be less than or equal the cap on the radiator

Excellent video. That is a real problem solving topic. I run a 2002 WRX in Arizona and it gets hot here. The stock configuration has done fine with +115° temps, but you cannot run the car hard during these times, obviously. Once you figure it out, I would love to improve my cooling system anyway possible. Videos like this are gold nuggets for us weekend warrior car builders. Thanks. 😉

The expansion tank vents to the coolant reservoir via a tube that is kept in coolant at all times. This allows the system to heat up and cool down, while pushing coolant in and out of the expansion tank without sucking air back in (which could lose your bleed of the system). Since the radiator vents to the top of the expansion tank, you want it to be able to push coolant out, but not pull anything back, because it could pull air back in and lose the bleed. The recommended way to set this system up basically allows for the proper regulation of pressure and control of thermal expansion in the system while having an ambient-pressure coolant reservoir available to the user and not allowing any air to enter the system. That being said, if you REALLY fill the expansion tank up, you probably won't ever get enough air in the cooling system to cause a problem, but if you 1. don't get the tank completely full, or 2. allow air to enter the expansion tank in some way (e.g. low coolant in the reservoir), you could end up in trouble.

Usually the radiator is the highest point, but because you have to cool the turbo and keep oil circulating you so you don't bake it if it put away hot. The turbo runs directly into the cap and as the water expands and heats it rises gets pushed out and cooler water from the engine is pulled in the expansion cap is there so that water can be forced in and out by the highest point and. And it's there directly to cool the turbo goes engine > turbo > expansion tank > radiator or overflow tank > engine , but you always want hot to be at the top of the system so that if it evaporates it likely out of the system atleast that's how I understand it. It basically a turbo timer but automatic and fully mechanical it's also nice because it forces the whole system to equalize to the radiator tank temperature also forgot about the forth hose that directly cycle just teh engine which is also the primary pumping method with the car on to cool the turbo by forcing coolant from the cooled side of the radiator into the water pump and engine and hot side of radiator I haven't rebuild a ej205 in a while it kindof faded, but that what I remember. My koyo didn't come with a cap also they're better than mishimoto. By a long shot. Aleast in terms of build quality.

The reason Subaru uses a higher pressure cap on the radiator and a lower pressure 2 way cap on the expansion tank is 1- it's easier to fill the radiator with a cap right on top, and 2- the expansion tank is higher in the system. If you flip the caps, it allows air into the system.

On track, with the stock configuration, I had an issue with pushing tons of coolant into the coolant overflow until the lower fluid capacity caused over heating. As a quick leap of faith, at my next event I replaced both caps with 2-bar 2-way caps and never had any overheating issues, nor over filling of the overflow tank. I was not aware of the Rad cap being a 1-way cap but it makes sense why my overflow was constantly overflowing and thus overheating. I will definitely be taking a handful of caps to my next event now that I know this, but the 2-bar 2-way cap combo I have currently seems to be working.. (Aftermarket Aluminum Rad and hoses handled the higher pressure just fine.)

I have been having this issue ever since my power bump. Going to check this out when I get the car back

Very interesting! Never would have considered this as such an important thing!

I had this issue happen to me. I have a Mishimoto radiator and the cap. I bought the vehicle with it set up like this. I noticed coolant on the top of the radiator and went and bought a basic radiator cap and never had an issue again.

I did read when I got my mishimoto radiator to installed their cap in place of the expansion tank and move the expansion tank cap to the radiator location. Besides the paperwork mentioning a 2 way cap I didn't look further to find the differences. I ended up not using the mishimoto radiator due to fitment issues (GM6 with GD7 swap) and I was just looking to replace both caps with new oem caps. I ended up with 2 high pressure caps that are shaped differently and thats when the concern arose. I was like "which cap do I need, is the 137kPa for STI and the 108kPa for WRX?" So I did digging and couldn't find anything concrete. Finally read through the service manual and it just explained which one goes where. I've yet to install the lower pressure cap on the expansion tank since I didn't see any cooling issues, but the swap is weeks old and only a couple hundred east break in miles on it. But I hace noticed my upper radiator hose pulls a vacuum after the engine is turned off and the hose collapses which caused the hose to rub on a pulley so I will install the 108Kpa on the expansion tank and see if that cures that small issue. Considering I built the car to go on track its good to see this information sooner than later. While we have our questions on our own builds, just goes to show how a team of engineers at subaru cobbled this solution and it works perfectly so long as the cooling system is being serviced per their procedures. Goes to show sometimes OEM is just fine in some applications.

I've ran two after market caps for 5 years now with zero issues with heat . Ones a Cobb cap for expansion tank made by aluminate and an apex cap on mishimoto rad . The combo works for daily tuned car , I feel stumped as you guys since many have told me not to do this but seems just fine

Awesome video. Here’s my experience and two cents. A few weeks ago I pulled the engine(04 EJ205) had the original aluminum expansion tank, the filler neck had a small rip due to all this pressure. Ended up changing to the plastic OEM expansion tank, but did not replace the caps. Anyways, my dad helped a bit, during the process of adding the oem super coolant(Have a 2007 2.5i A/T sitting on the side) Did notice the shape where different(didn’t give too much thought)and did not check the kPa. A few moments later my dad brought this up even though he’s never worked on an EJ. And mentioned to check the pressure readings on top of the caps, without even looking at them. Once I did.. for radiator it’s 108 kPa and expansion tank 137 kPa. Looked it up on forums and saw the difference. No overheating or anything. Mean while I still kept inspecting hoses and caps. I’d remove the expansion tank cap and see build up from I guess the old coolant. I clean it up with a toothbrush and remove the gunk. Radiator cap not a whole lot. You explaining how these caps work, specially the expansion tank cap, gave me an answer to my question tonight. Earlier today(9/23/22) took a drive from chicago to Wisconsin dells(non stop). Just check my engine bay and saw the upper radiator hose kind of swollen, pressure wasn’t released from the expansion tank cap(since I didn’t clean it before hand). I’m gonna get a cheap toothbrush and clean it. Until I get new OEM caps. This video helped me understand how these caps work, so thanks for that!

I hope I can provide a bit of insight to the reasoning between pressures and locations. The radiator located cap is a one way valve so should an over pressure condition occur pressure will be released. It is a one way valve because that is not the highest point in the cooling system. The cap located on the expansion tank should be a marginally lower pressure release as you want that cap to be the main point of coolant expansion overflow. Being the highest point in the system, it will aid in burping the system. You also want this to be the place where the two way valve allows coolant to be sucked back up through to refill the cooling system from the highest point.

Well what’s funny is I think the second cap in Subaru is to eliminate the air pocket that forms and for some reason a Subaru water system is hard to bleed air out of. I am relocating my expansion tank and radiator cap to the high point so I can get the air out easier during refill or flushing coolant. And I use 1 cap and it’s a 2 way.

I'm not claiming to be an expert, but I'd like to offer my anecdotal 2-cents, in case it is useful as a datapoint for anyone researching this subject: I have been running a Mishimoto radiator on my 2011 WRX for roughly 3 years now. For the radiator itself, I purchased and installed an OEM STi 1.3 bar radiator cap, which has a slightly higher pressure rating than the stock WRX's cap IIR, and still retains the 1-way valve construction. On the expansion tank (or what I sometimes call the turbo reservoir, higher up on the engine), I placed the aftermarket 1.3 bar Mishimoto cap there. So there is no pressure differential between the two caps, and the higher cap in the system is a 2-way Mishi valve. I also installed Samco's silicon ancillary coolant hoses at the same time as the radiator. 90 degree summers, highway/stop-and-go traffic, occasional performance driving (not extended track use though), and I've had zero issues. The overflow tank will fill up when hot, and drain back into the engine upon cooling. Will be watching closely when I start HPDE courses within the year.

This bit my ass badly. I finally communicate with Mishimoto radiator they told me the same thing. I ended up just running 2 oem caps and no issues. This should be a large red warning on the cap when they ship it. Not a foot note on paperwork nobody reads.

Thanks again for all the information and answering all my build questions a few weeks ago. Another thank you for this very important information because after watching this and putting the knowledge to an issue I'm having in my semi I think you may have indirectly solved my issue there as well 😃 although it's not an overheating issue.

This is an interesting thing of 2-way and 1-way radiator caps. When I owned my 1999 Legacy B4, it was an OE twin turbo EJ20 set up and only had the overflow tank next to the intake manifold and no cap on the radiator. I was plagued with over heating issues and thought it was a head gasket issue. After replacing head gaskets and rebuilding, could never get it to properly work right (coolant overheating). Would always overheat at idle (like an air pocket after cold start), burp it, it would be fine. Could never figure it out. I now wonder if I had a wrong radiator cap. Of course, I’ll never know as I scrapped it already 😢. But thank you for some insight and sharing!

It doesn't make sense to put the 2-way radiator cap on the expansion tank and the one-way cap on the radiator because when the cooling system cools down, it contracts and there is no pulling of the coolant from the expansion tank due to the missing 2nd valve for vacuum. If the radiator has the 2 way cap and the expansion tank (which is only a reservoir) has the one way cap, coolant can be pulled back into the cooling system via the 2 way valve on the radiator. Vacuum pulls the 2 way valve open pulling coolant from the reservoir into the radiator.

Such a simple concept is making my head hurt. Crazy how many years I’ve been messing around with these cars and have never encountered this issue. NOTE TO SELF: don’t swap caps. Thanks guys!

IV had really good luck with my 1.3 bar 2 way radiator cap, I have one radiator cap and seams that moving the expansion tank to the high point mine is right behind the intercooler, and in an 85 rx turbo the spare tire cubby works perfect to mount the catch can and expansion tank and set tools on when your working on it.

On my 04 sti I used to own it had a cap on the actual radiator and on the expansion tank reservoir. Ive had installed the larger Koyo radiator when I did one of my 4 engine builds and that radiator expanded from pressure in the cooling system and if I can recall had a head gasket failure. Probably due to not having a dual valved radiator cap on the expansion tank. Fast forward today now I own a 2018 Civic Type R which has an expansion tank and the radiator is cap-less. It is well known that these cars overheat on the track. I’ve done several cooling enhancement mods as well as a fully built motor and big turbo upgrade. Since then it hasn’t over heated. I think mainly from running a bigger turbo. I think maxing out the stock smaller turbo which caused more back pressure making it into a heat pump. The larger turbo has less back pressure so it’s not producing as much heat.

love your channel but its in dire needs of some better audio equipment but overall amazing stuff! thanks for sharing all this info

What an huge amount of info... And what about the non-turbo subarus, with only one cap in the radiator and the expansion tank next to the radiator, with an standard plastic yellow cap? This cap on the radiator is a two way one?

wow that's a good video on overheating issue subaru

Appreciate the info thank you..I was looking for aftermarket caps and could not decide which to get..I'm glad I went oem for this time around.. cheers

I have literally been dealing with this for a year now trying to figure out why I can’t keep temps down

They never tought us anything what so ever about this in subaru factory technician training courses... I must have been very lucky over the years because I ran installed and sold tons of sti and greddy radio cap sets and never had an issue...that I was aware of anyway.... but makes a ton of since tho knowing the difference and how each work

I'm definitely curious of your findings with the testing. I'll be looking for future videos. I run a Mishimoto radiator with the Mishimoto cap on the expansion tank. I think the OEM expansion tank cap is on the Mishimoto radiator. My car gets warm on track, but does not overheat. However, I have to run the heat when the ambient air temp gets over 85* otherwise it gets too hot.

I have an 05 LGT, does this or how does this apply to the KoyoRad Racing radiator? Didn't see any notes for this product.

I had a cooling issue due to running the mishi cap on a mishi radiator.. I think the main contributing factor is the expansion tank is the tallest point on the cooling system, therefore the two way valve needs to be there to allow coolant from the overflow tank to flow back into the cooling system properly. If you have a two way cap on the radiator, and a two way cap on the expansion tank.. then the coolant from the overflow doesn't have pressure to flow back into the cooling system.

thanks, just installed aftermarket radiator directly for WRX. Of course the cap which came with the radiator is two valve and without this video I will run it without knowing it. I will keep stock ones then

I bought a metal Mishimoto expansion tank for my '03 WRX. Their brand new cap (identical to the one shown in the video at 2:28 and 2:36) leaked so i replaced it with an OEM cap. I have new OEM caps on order to replace the 19 year old ones. Reference 4:45 it is stated that the 02/03 WRX did not have a radiator cap. I can't confirm or dispute that since i got a "free" radiator from my Subaru dealer when they poked a hole in it while replacing the timing belt. There are two caps listed for the 02/03 WRX: 45137FE002 Cap (Round) 45137AE00B Cap (Round with two ears to grab onto)

I called and talked to Mishimoto about this 5 years ago haha I had that Mishimoto cap on the expansion and a Koyo on the rad for awhile no issues but then switched to the Koyo on expansion and a JDM STi cap on the rad (yes mostly for looks on both) but no issues, have only pushed the car on a California canyon run, no track time.

I run two oem 1.3psi caps on my forester xt, 1 for the tank and 1 for the mishimoto radiator. No issues after many years. I also did the same with my legacy specb, but with koyo rad this time. Still no issues. Just run 2 oem 1.3 caps

I didn't think I would watch an 11+ minute video about radiator caps today. Not sure why either, I don't have a Subaru , and on my lawnmower I have replaced the cap with a taped on shot glass.

Well im running an Aftermarket Aluminium radiator with no Cap provision at all and just a cap on the Expansion Tank ,should I be running a Two Way Valve Cap????

I've got a Koyorad rad on my 05 STI. Should I just run the stock caps on the expansion tank and radiator? What about these 1.3 bar caps, including the pink STI cap? Does that go on the expansion tank or radiator?

Dealer OEM caps on Japanese cars gor for about $20. give or take. Seems pricy compared to local auto parts store that are $5. However, dont cheap out on caps. If you are going after market buy a good quality cap. It may cost you about $25. But again, dont cheap out. I use the cap that goes on my Megan racing radiator 1.5 years later. No issues at all. I do keep a Honda oem cap in my glove box for backup.

So, if the reason Subaru put the second cap on the radiator was to keep the seams between the aluminum core and the plastic from leaking, why does the all aluminum aftermarket radiator need it?

Always learn something new from watching your videos, awesome work guys, I have an early WRX with no cap on the radiator, just an expansion tank with a cap, have I understood you correctly in that the expansion cap should be a two way valve?

A couple of years ago I got a radiator flush at a Subaru dealership and they accidentally swapped the cap locations when they were done. Started hearing intermittent burbling noises in the dash and discovered what they did 🤦🏻‍♂️

Wow good info. I actually thought these caps were interchangeable

Question! Is the expansion tank a factor when doing coolant flushes/replacement? Or only do burping from radiator like all other cars with no expansion tank..?

Hello guys so which cap should have the higher pressure the one on the expansion tank or higher level cap or the pressure relief valve that Subaru calls it which is the radiator cap that's in front of the car

So I have a 2018 wrx with the mishimoto radiator and the mishimoto radiator cap… I have the stock expansion tank with the stock cap on it… I’ve been running the mishimoto radiator cap and my cars been overheating… could that be my issue ? Should I go back to the stock radiator cap?… I only have about 2 weeks with this set up

Running CSF 1.4 cap on the radiator and HKS 1.1 on expansion tank no issues so far but hopefully you guys will come out with a better looking one way cap

Does this 2 cap solution also apply to the Subaru Outback...?

So I just bought a Koyo Radiator and a koyo cap, the SK-C13 and it’s a two way cap. I thought the expansion tank got the two way cap and a one way cap for the radiator? Your webpage says the regular cap doesn’t fit the Koyo radiator, they look the same to me though. Should I try to fit a regular one way cap? Looks like I should return the Koyo cap. Well I’m off to watch the video of why you all got rid of your radiator cap now. Cheers

So my caps have been fine but I just did a coolant flush on my 18 STI Two days ago but the coolant was only 3,000 miles old but I’m diagnosing something but anyway my coolant hoses are collapsing under vacuum once it cools off. So I’m curious if I could clean the cap on the radiator because I had that oily residue that I messaged you guys about the other day. Crazy thing is I don’t see the oil coming in but right now I’m trying to figure out the hose issue. I also notice the coolant level will lower just a little but it’s not leaking or anything like that.

Flow Dynamics can also cause issues , (modify) engine usually Create way more heat than the (block ) was engineered to dissipated/ pressure /flow may have a max efficiency with the infinite variables of block differences , Maybe equalizing flow with a (4 cylinder cooling mod ) I currently have a expansion tank deleted with an AOS as *high point, with radiator cap* after market radiator . it pulls and pushes coolant in to the reservoir no problems or overheating has occurred

OEM Radiator Cap www.flatironstuning.com/subaru-oem-radiator-cap OEM Aux Tank Cap www.flatironstuning.com/subaru-oem-aux-coolant-tank-cap

Do I burp air at the expansion tank or on the koyorad radiator cap ????. I just did this on the koyorad side. Was this wrong ?

freaking mind is blown

And what is the route with koyorad ? Is the same ? Is koyorad coming with his own radiator cap ?I don't wanna mishimoto rad on my STi...

Any info about koyo rads? I habe a 2011 wrx, installed koyo rad and bought the koyo red cap that says 1.3 kgf/cm2. Should I put this on the actual aluminum rad or expansion tank?

I fully sealed and capped off my mishimoto rad cap so it won’t allow anything out. Kept oem cap on upper reservoir and it’s been fine ever since.

Also my 99/00 model WRX GF8 Wagon has Metal end tanks on the radiator and so do all the other proper WRX's 1994-2000

So which radiator would you suggest for longevity and cooling of the car for daily and lite track use?

My 22 WRX only has one radiator cap. At least the only one I can see.

So for a rotated setup without an expansion tank use the stock cap or aftermarket 1.3? 1.5? Curious

Why doesn't mishimoto just make a single way cap that we can buy?

For clarity, with an AM Radiator like the Mishimoto, can I use the Factory Caps in both locations; Radiator and Upper Reservoir?

So I am running a Mishimoto expansion tank and a Mishimoto radiator. And as you know they both come with the Mishimoto caps and I was running both but I noticed my car would over heat if idled for too long. Winter wouldn't really happen much. So I'm sure this is my issue, what should I do for caps? Should I buy an oem "expansion tank cap" and put it in the Mishimoto radiator? Will it fit?

Is that the marsh composites reverse scoop hood I see in the track footage? Man I ordered mine in march last year so I should be seeing it soon? I hope? 😂🤞

So the stock expansion tank cap, it is already a 2way?

I just had to replace the radiator in my 2010 Subaru Forester non-turbo. They put a new cap on my new radiator. However, I'm confused to which cap needs to be on the radiator now. The cap they have on it at the moment has two ears. Is this a two way cap. If so, do I need to replace this cap with a one way cap... without the ears.

I'm running a Stage 2, 2002 WRX with a Mishimoto replacement (oversized racing) radiator with their valve on the radiator and Subaru's OEM one on the expansion tank and I have no overheating issues with my coolant (only the oil gets hot when sitting in rush hour style traffic). I don't really see the point in swapping them, but am curious to know more and as to why they did have an overheating issue?

I have the early STI style single cap system & really can;t understand the disadvantage - pretty much all cars have a single 2 way rad cap.... I thought the additional cap added to the radiator was purely because some people weren;t patient enough to bleed the system properly.

Hmm, my 2014 Impreza I only see one radiator cap...

Can someone with a factory bone-stock subaru chime in and take a look at which cap goes where? [EVERYONE]: "Stock subaru?" *crickets*

I know I’m late but the consensus is to just run the stock radiator caps with any radiator?

I have a jdm 99 gc8 sti it only has one cap on the top turbo tank and the radiator has side tanks no failures yet 205,000km going strong

i have a question about the pcv system. when i installed my IAG Competition AOS i completely removed my entire pcv system & just have all 3 breather ports ran into the AOS, and the return hose ran back to the crankcase breather port. Is my engine going to be ok without the pcv valve in said system, or do i need to reinstall the valve back on top of the crankcase breather port?

I'm still confused on the radiator caps. i have a Mishimoto radiator and I have the Mishimoto cap on the radiator and it seems to run fine. should I do what Mishimoto suggested and swap the OEM expansion tank cap on to the radiator and the Mishimoto cap on the expansion tank?

Subaru/STI runs a high pressure STI radiator cap on the expansion tank of their Nurburgring car…

Hy my subaru has 2 caps the radiator cap its written 1.1 abd the one on the engine its 108kpa. What if i put both 108kpa what will happen coz i can only get 108kpa??

I’ve had issues with radiator caps a few times myself.

Hey guys, great video! So im currently having an issues with my coolant system for my 2013 wrx. I got a new radiator, radiator hoses, expansion tank and overflow tank. My radiator was oem that i purchased and it was without the oem cap. The expansion tank came with a mishimoto cap and i just put it aside and ordered 2brand new expansion/ radiator caps. After some new coolant and full burp of all air bubbles(properly done through the expansion tank) and is ready to go. I also order new thermostat, thermostat housing, and sensor. With nearly everything brand new, why am i still having problems with my overflow tank filling up and spewing out. When the car cools i never see that the coolant pulles back into the radiator. Ive done pressure tests and the head gasket is fairly new. Im completely lost by this? Is this setup not brand new?! Also my radiator fans are turning on and my car stays within 197-178range. Drove it around for an hr keeping tabs on the temps. Any ideas please help?

The mishimoto cap must be a lower pressure cap the the expansion tank cap, otherwise why even use mishi cap?

Please post the a as soon as you have figured out the best combination 😅 . Also since the expansion tank is a plastic one , which aluminium aftermarket one would you recommend ? Ths from Italy

Can the turbo legacy radiator cap (137 kpa) work on the non turbo radiator?

Heya great video thank you .! question if i may.. i have built myself a closed deck forged 2.0 ej and am running a aluminium aftermarket radiator with no cap . from what i am reading should i be running a larger expansion tank ie the mishimoto one with a 2 way valve ?

So the overheating issue is solved? Im surprised.. lol... Anyway i often see people swap aftermarket radiator cap...whenever they swap yo aftermarket radiator... which i will always try to make sure that higher pressure cap installed on radiatot.. not the expansion tank... Because ive alway have this thought that with expansion tank.. u dont want coolant going out somewhere else at lower pressure than the tank... So with this service manual on 2types of radiator cap story... These explain further and support my theory on this.. Thanks for bringing this up 🍻 cheers

As you do research I think Thomas said he doesn't run radiator cap on his radiator

So can you leave both caps oem or do you have to run the mishimoto cap on the expansion tank?

I was just about to order the radium engineering caps from you guys and I'm glad I didn't. Just going to use OEM caps and be done with it so there is no guessing on a freshly built motor. I see radium has a style A and a Style B. Is one of them a one way and the other a 2 way?

They are telling the thermostat to open at different times.

What's funny about my ej255 with mishimoto rad and proper cap, plus oil cooler, on track I still purge coolant, even though I pass a pressure and exhaust gas test, never overheats though 😜 i just have to pour the coolant from the overflow back into the top tank, then let er rip some more.