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So I'm pulling my 2014 STi out of storage on Monday and I'll be performing the cylinder #4 cooling mod in a few weeks. I'd like to learn of any tips or trick the community has for performing this. Namely:
  1. When draining the coolant, is it best to just pull the lower hose on the radiator? Or should I remove coolant from other orifices. I've never drained this coolant system before. So I'd like to remove as much as possible.
  2. I've seen a few videos of others performing this mod using various kits (VEM, GETADOM, etc.). I've seen some use the lower heater hose and some use the upper heater hose. I was under the impression that the lower hose was correct because that is the return line to the water pump. Is that correct?
  3. I'm not super familiar with the cooling system in my car. Does the line to the water pump route the coolant the the radiator?
  4. Just a point of interest question. I'm guessing that there is plug on the driver's side head because of the plug on the head on the passenger side that goes to the turbo AND the heads are just cast from components of the same mold or some other manufacturing practice like that. What do yinz think about that?
Any other advise is truly appreciated. Some think this forum has been losing steam but I think we're just finally starting to get down to the nuts and bolts of topics by learning the strengths and weaknesses of our cars and really starting to address them.
 

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There should a drain plug on the right side of the radiator on the bottom. This offers a smaller more controlled drain option rather than a massive dump of all your coolant everywhere except the drain pan. Just take off the rad cap first.

As for the plug, there is likely a factory block off plug Subaru has installed for single turbo applications. Dare I mention that Subaru has a part number for a threaded port for the left side head for a coolant source to their twin turbo applications. My 2008 WRX has a block off plug on the left side.

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I'd expect the overall coolant temperature to increase a bit with this mod for 2 reasons:
  • The coolant mod allows some amount of coolant to bypass the original path through the radiator (from cylinder 4 -> heater hose -> water pump housing inlet -> cylinder 2). While probably a minimal amount, it does reduce the percentage of coolant passing through the radiator.
  • This mod claims to reduce the cylinder 4 "hot spot" which would mean that the coolant is absorbing more heat from cylinder 4 further increasing coolant temps.
There is some good debate starting on page 2 & 3 of this thread:
 

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I'd expect the overall coolant temperature to increase a bit with this mod for 2 reasons:
  • The coolant mod allows some amount of coolant to bypass the original path through the radiator (from cylinder 4 -> heater hose -> water pump housing inlet -> cylinder 2). While probably a minimal amount, it does reduce the percentage of coolant passing through the radiator.
  • This mod claims to reduce the cylinder 4 "hot spot" which would mean that the coolant is absorbing more heat from cylinder 4.
There is some good debate starting on page 2 & 3 of this thread:
One or two degrees is negligible and could be chalked up to any number of reasons. If, and purely hypothetical speaking, there's a 10 degree consistently higher temp, I'd say Dom may need to rethink his routing and work on revisions. Sure cylinder 4 may very well be cooler than it used to be, but now the rest of the engine is running hotter, which will have a negative effect on intake air density which means less horsepower (the smaller the increase, the more negligible the effects). Kinda counterintuitive, wouldn't you say?

Alternatively, if anyone is that concerned about it, they could reroute the cooling mod hose to a different spot, perhaps one that feeds the radiator instead instead of the water pump. I'm certain I've read Dom used the heater core lines purely for convenience, as it's literally right there.

Subaru used a crossover tube on their twin turbo setups that connects to the turbo coolant tank (see links below). You could use Dom's head plug, reroute a longer hose over the transmission, secure it away from important parts and wiring harnesses and use Dom's T-connector into the existing coolant return from the passenger side turbo.
 

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... Sure cylinder 4 may very well be cooler than it used to be, but now the rest of the engine is running hotter, which will have a negative effect on intake air density which means less horsepower (the smaller the increase, the more negligible the effects). Kinda counterintuitive, wouldn't you say?

Alternatively, if anyone is that concerned about it, they could reroute the cooling mod hose to a different spot, perhaps one that feeds the radiator instead instead of the water pump. I'm certain I've read Dom used the heater core lines purely for convenience, as it's literally right there.

Subaru used a crossover tube on their twin turbo setups that connects to the turbo coolant tank (see links below). You could use Dom's head plug, reroute a longer hose over the transmission, secure it away from important parts and wiring harnesses and use Dom's T-connector into the existing coolant return from the passenger side turbo.
The rest of the engine running hotter is true, but it's now balanced. It will be very negligable and might be zero if the systems capacity is adequate. An aftermarket radiator and/or water pump upgrade could easily overcompensate.
Sure you could dump the flow out of the head almost anywhere but it might well upset the pressure balance of the coolant flow and change the cooling characteristics of the engine. I know that Dom had thermal sensors all over the engine as he developed and tested his design.
Lastly, the Subaru plug with nipple might work, but the internal diameter is critical to the design. Someone would have to check that before using it. I suspect it's too big. A restrictor might be needed and then you're back to custom parts. I'm not going to say more as I think Dom deserves to make a few bucks for his design and testing work.
 

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Discussion Starter #8
The rest of the engine running hotter is true, but it's now balanced. It will be very negligable and might be zero if the systems capacity is adequate. An aftermarket radiator and/or water pump upgrade could easily overcompensate.
Sure you could dump the flow out of the head almost anywhere but it might well upset the pressure balance of the coolant flow and change the cooling characteristics of the engine. I know that Dom had thermal sensors all over the engine as he developed and tested his design.
Lastly, the Subaru plug with nipple might work, but the internal diameter is critical to the design. Someone would have to check that before using it. I suspect it's too big. A restrictor might be needed and then you're back to custom parts. I'm not going to say more as I think Dom deserves to make a few bucks for his design and testing work.
I've also seen videos of Dom explaining his process and he does provide data showing equalized temperatures across the engine. The point about meeting up with the turbo return line is interesting and I would be curious to know whether or not Dom examined that possibility. Does anyone know if he posted a video expanding on that?

There are some good opinions here. However, unlike Dom, none of us have data to back up our claims. Not sure who said it but one of my favorite quote, "without data, you're just another noisy opinion".
 

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... There are some good opinions here. However, unlike Dom, none of us have data to back up our claims. Not sure who said it but one of my favorite quote, "without data, you're just another noisy opinion".
I can give you anecdotal, experiential and observational data. I have it on my race car and it runs good! Happy as a clam at 470 HP for 20-30 minutes at a time for fifty hours now. Plugs and compression look good.
I have it on my 400 HP DD and when I ran it at Watkins Glen I experienced detonation and it got that knock thingie our engines get. I think that was Dom's fault. So, I can say that the mod does not prevent rod bearing failure on #3. ;)
I hope everyone see's I'm joking about the efficacy. It has not been a problem on my cars or another friend's track car I did it to. It makes perfect sense to me, as a semi-engineer.
I will monitor EGT's on all cylinders on the next race build, but that's not going to prove anything.
Who of us are going to stick sensors all over the heads and in water jackets to collect the data? Dom's the one with the related degrees and experience. I flunked out...
 

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Discussion Starter #10
I can give you anecdotal, experiential and observational data. I have it on my race car and it runs good! Happy as a clam at 470 HP for 20-30 minutes at a time for fifty hours now. Plugs and compression look good.
I have it on my 400 HP DD and when I ran it at Watkins Glen I experienced detonation and it got that knock thingie our engines get. I think that was Dom's fault. So, I can say that the mod does not prevent rod bearing failure on #3. ;)
I hope everyone see's I'm joking about the efficacy. It has not been a problem on my cars or another friend's track car I did it to. It makes perfect sense to me, as a semi-engineer.
I will monitor EGT's on all cylinders on the next race build, but that's not going to prove anything.
Who of us are going to stick sensors all over the heads and in water jackets to collect the data? Dom's the one with the related degrees and experience. I flunked out...
Thanks for the info. My car isn't a race car or a DD. Just a fun-mobile right now. But my goals for the car right now are to address as many of the inherent fault in the EJ25 as possible and maintain it regularly before adding more power in an aggressive manner.

Cheers.
 

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Stock plug is 12.7mm ID. Dom's is 10mm ID. Will that difference in ID make a difference? Absolutely. Are you going to blow up your motor in some epic way if you don't bow to Dom and buy his kit? Doubtful.

Since Dom seems to be the only one who has tested this mod so far, I'd love for him to test Subaru's plug and compare notes. Better yet, share the data/results of using a larger ID as he indicated that he did try larger and smaller ID's.

He mentioned somewhere he purposely left cyl 4 hotter than the rest and I don't exactly remember why, but this reason is why he didn't go with a larger ID is to have cyl 4 still the hottest cylinder of them all, albeit cooler than it was before. The reason has something to do with the knock sensor placement over #4 as the ECU is supposedly programed to listen for knock with #4 being the hottest, or something along those lines. This seems more of a calculated theory to me, as in no one can find information to the contrary so let's go with it. "Critical" isn't a word I would use, at least as it sits without seeing data from other sized ID's. From what I've seen so far, he's only shared data on his final 10mm ID product and has made an honorable mention that other sizes didn't sit nicely with him. So, settling on a 10mm ID seems more so a personal preference than it was an absolute necessity, as Subaru has a similar plug for their twin turbo applications and they obviously would have put the engineering and testing into settling on that size ID. Subaru isn't successful because they just slapped some parts together with zero data and said, "yup, let's get these things sold." The fact that Subaru ran their #4 plug to the right side and T-ed to the right turbo coolant return and not either of the heater core lines tells me the coolant return is a better option than Dom's. The left turbo would heat the coolant even more before dumbing it on the right side return and there's little issues with cooling that I can find as a result of two return lines plummed to the turbo expansion tank. So, I don't completely buy the line that Dom's kit is better than using Subaru's plug in a DIY kit.

The knock sensor can still accurately determine a misfire/knock on other cylinders with or without Dom's kit. If this isn't the case, then codes like P0301, 302, 303 are basically meaningless and leave us blind as to where a misfire problem actually is.

Is be obligated to share that information? Opinions vary and we all know how stating opinions go on the internet. Why would he? He doesn't want people to make their own kits but instead buy his. I guess I'm just accustomed to guys like Gale Banks educating people with a more complete picture. I will say, however, as a data/information junkie, that the complete picture is missing and considering I don't have access to cool equipment as Dom does, I rely on this information to help me better understand what's going on. How much of a difference does 2.7mm make? Will #4 be so cool it drops below the others or will it still be the hottest but more evenly matched? If nobody here, except Dom, can answer those questions, then the hype on his kit stems, in part, from Dom's fan club and marketing. So far, we only have two points of reference: no cooling mod and Dom's. Yes his kit is an improvement and that's good enough for most people. Personally, I'm only 60% sold that his kit is the be-all-end-all. Not enough to fork out my hard earned, as "cheap" as some may consider his kit to be. I like to make sure that my money is well spent, not have 40% doubt that I made the right choice.

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I drained the coolant at the radiator plug, but still had some residual coolant in the heater return line when I went to cut it. Maybe I could have drained more from the water pump connection to the lower radiator hose after coolant stopped draining from the radiator? Just make sure to have some eye protection and rags standing by.

For the factory block off plug, make sure you have a 12mm allen head socket (3/8" or 1/2" drive) and some type of thread sealant for the port you are installing. If you are using the GETADOM kit, you could use a 1" deep socket to tighten it (without the hose installed) to the head, but might be a pain to get the hose clamp on.

I'd say the most helpful video for me was by OCTurboJoe.
 

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Discussion Starter #13
I drained the coolant at the radiator plug, but still had some residual coolant in the heater return line when I went to cut it. Maybe I could have drained more from the water pump connection to the lower radiator hose after coolant stopped draining from the radiator? Just make sure to have some eye protection and rags standing by.

For the factory block off plug, make sure you have a 12mm allen head socket (3/8" or 1/2" drive) and some type of thread sealant for the port you are installing. If you are using the GETADOM kit, you could use a 1" deep socket to tighten it (without the hose installed) to the head, but might be a pain to get the hose clamp on.

I'd say the most helpful video for me was by OCTurboJoe.
I saw someone use a 1" crows foot and extension. That looked legit.
 

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Stock plug is 12.7mm ID. Dom's is 10mm ID. Will that difference in ID make a difference? Absolutely. Are you going to blow up your motor in some epic way if you don't bow to Dom and buy his kit? Doubtful...

Since Dom seems to be the only one who has tested this mod so far, I'd love for him to test Subaru's plug and compare notes. Better yet, share the data/results of using a larger ID as he indicated that he did try larger and smaller ID's.
... How much of a difference does 2.7mm make?
This rant is asking Dom to test something that is 38% bigger. THAT MUCH. Go ahead and question someone that's worked on nuclear subs and designed and built Subaru engines for airplanes. You can't just start selling aircraft engines out of your garage... Yes, you should bow to Dom.
I think you should go back to your obvious expertise, COVID 19.
 

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This rant is asking Dom to test something that is 38% bigger. THAT MUCH. Go ahead and question someone that's worked on nuclear subs and designed and built Subaru engines for airplanes. You can't just start selling aircraft engines out of your garage... Yes, you should bow to Dom.I think you should go back to your obvious expertise, COVID 19.
I can test cylinder head temps at the coolant port with my laser temp gun just like Dom did in one of his videos, but individual cylinder EGT's is not a setup I have nor have any use for as I don't have a car that needs it so I tend to rely on the plethora of information that is researched by other people. Being that I have multiple interests, surely you wouldn't suggest that I pursue a career in all of those fields just so I can have access to the required testing equipment to appear more "legitimate" on the internet? Education and pieces of paper don't impress me.

Considering there's been reports of reduced cabin heater performance with Dom's kit connecting to the heater core return in areas where it gets cold (which could be problematic for those who daily drive in -40F temps), it's clear the heater core lines are not the most ideal location to dump the cylinder head coolant, perhaps at least not as far as daily drivers go but I guess the owner has to decide which trade-offs are acceptable. This heater reduction may be why some guys have put the T in the heater core supply..??

A much more logical solution is as I suggested above based off of Subaru's designs: use Dom's magical 10mm ID plug and T, run a longer hose to the coolant return on the right side of the engine as that does feed the radiator, which is what Subaru did and spoiler alert, they didn't just build the engines...

Do you know why Subaru settle on 12.7mm ID? I don't. Why not an even 12.5? Or 13? Does Dom know? I doesn't sound like he cares. If that's the case, he too lacks a more comprehensive and complete picture. Did Subaru test smaller and larger diameters? Probably. So what makes Dom better than Subaru?

Interesting response though. I present some ideas and questions in the interest of curiosity and I get told to be a sheep... I didn't ask him to do anything. lol I said I would love for him to test it or share the data he already has as I doubt he randomly chose a 10mm ID, saw improvements and was immediately satisfied.

I'm going to assume you're the one who "worked on nuclear subs and designed and built Subaru engines for airplanes"? Working and building is different than engineering. Based solely on that information, it sounds to me like you were just a wrench monkey with a calculator following a set of equations that someone smarter discovered. But would you like try your math again? I don't need a calculator to know that 38% bigger of 10mm does not equal 12.7mm. 38% more more flow, maybe. (Not bad math's for a COVID-19 expert, hey? P.S.: I can pull up pipe flow calculators on Google, too). In addition, I never said his kit wasn't effective so I don't know why you're getting hurt feelings. A curious mind and some one who has real intellect is open to discussion...

Even then, what does 38% mean? Does it equal 38% cooler EGT's as it pertains to Subaru engines? What difference does it have on coolant temps and cyl 4? What radiator was Dom using when he obtained his results? Any on-road testing and data or was this all "in a lab"? Was a reason why he chose a 10mm ID simply to reduce impact on the heater core output while balancing Cylinder 4 coolant temp reductions? Would he have used a larger ID if the heater core wasn't a factor in his kit design (if it even was to begin with)? Or was it solely because of the knock sensor placement?

I'm confident he knows a thing or two, but he's not the god-send some people seem to think he is. He's presented a solid idea and given us a good starting point. If that's good enough for you, then that's all you need. Continue throwing parts and upgrades on your car without a solid understanding of what they are actually doing. But for some who have questions, considering how recent this kit is, these are important discussions. It was once thought that the OEM UEL exhaust headers was the culprit of Cyl 4 issues and everyone went UEL vs ELH crazy, but it seems that didn't have as big of an impact as once thought. So forgive me for asking questions. I would hope and like to think Dom has a lot more data than he is giving but I'm not easily impressed by people who throw around job titles and accomplishments.

My experience and "expertise" is immaterial, especially on the internet. I can tell you one thing though, Virology isn't it.

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I can test cylinder head temps at the coolant port with my laser temp gun just like Dom did in one of his videos, but individual cylinder EGT's is not a setup I have nor have any use for as I don't have a car that needs it.

Considering there's been reports of reduced cabin heater performance with Dom's kit connecting to the heater core return in areas where it gets cold (which could be problematic for those who daily drive in -40F temps), it's clear the heater core lines are not the most ideal location to dump the cylinder head coolant, perhaps at least not as far as daily drivers go but I guess the owner has to decide which trade-offs are acceptable. This heater reduction may be why some guys have put the T in the heater core supply..??

A much more logical solution is as I suggested above based off of Subaru's designs: use Dom's magical 10mm ID plug and T, run a longer hose to the coolant return on the right side of the engine as that does feed the radiator, which is what Subaru did and spoiler alert, they didn't just build the engines...

Do you know why Subaru settle on 12.7mm ID? I don't. Why not an even 12.5? Why not 13? Does Dom know? I doesn't sound like he cares. If that's the case, he too lacks a more comprehensive and complete picture. Did Subaru test smaller and larger diameters? Probably. So what makes Dom better than Subaru?

Interesting response though. I present some ideas and questions in the interest of curiosity and I get told to be a sheep... I didn't ask him to do anything. lol I said I would love for him to test it or share the data he already has as I doubt he randomly chose a 10mm ID, saw improvements and was immediately satisfied.

I'm going to assume you're the one who "worked on nuclear subs and designed and built Subaru engines for airplanes"? Working and building is different than engineering. Based solely on that information, it sounds to me like you were just a wrench monkey with a calculator following a set of equations that someone smarter discovered. But would you like try your math again? I don't need a calculator to know that 38% bigger of 10mm does not equal 12.7mm. 38% more more flow, maybe. (Not bad math's for a COVID-19 expert, hey? P.S.: I can pull up pipe flow calculators on Google, too). In addition, I never said his kit wasn't effective so I don't know why you're getting hurt feelings. A curious mind and some one who has real intellect is open to discussion...

Even then, what does 38% mean? Does it equal 38% cooler EGT's as it pertains to Subaru engines? What difference does it have on coolant temps and cyl 4? What radiator was Dom using when he obtained his results? Any on-road testing and data or was this all "in a lab"? Was a reason why he chose a 10mm ID simply to reduce impact on the heater core output while balancing Cylinder 4 coolant temp reductions? Would he have used a larger ID if the heater core wasn't a factor in his kit design (if it even was to begin with)? Or was it solely because of the knock sensor placement?

I'm confident he knows a thing or two, but he's not the god-send some people seem to think he is. He's presented a solid idea and given us a good starting point. If that's good enough for you, then that's all you need. Continue throwing parts and upgrades on your car without a solid understanding of what they are actually doing. But for some who have questions, considering how recent this kit is, these are important discussions. It was once thought that the OEM UEL exhaust headers was the culprit of Cyl 4 issues and everyone went UEL vs ELH crazy, but it seems that didn't have as big of an impact as once thought. So forgive me for asking questions. I would hope and like to think Dom has a lot more data than he is giving but I'm not easily impressed by people who throw around job titles and accomplishments.

My experience and "expertise" is immaterial, especially on the internet. I can tell you one thing though, Virology isn't it.

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Half the time you talk like someone who's mad about something, then you sprinkle in a bit of intelligence and then you sometimes just get things wrong. Anyone can be an armchair quarterback. For us in the trenches doing this stuff, we usually, at some point, say something is good enough. Sometimes just before race day.
I see you are doubling-down on the post length...
I doesn't sound like he cares? (sic) Are you a shrink? Dom has an interesting demeanor in his videos, but he has bothered to speak to me personally at length and we've had many in-depth email exchanges. Dom is smart. Really knowledgeable about Subaru engines! Eccentric perhaps? Most smart people are.
If you install the kit backwards it could wreak havoc. A "T" can influence the flow. A "Y" would be better, but a high quality running Y might increase costs.
Dom is the one that's worked on nuclear subs and designed and built Subaru engines for airplanes. Perhaps slow down a bit as you start to get inflamed by my comments?
Dom had sensors attached, which he collected data from AND also did shots with an infrared thermometer gun.
YES, it's 38% more more flow! That's huge.
You're forgiven for asking questions, but I don't get the attitude. You can be a twit with or without a degree.
 

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Half the time you talk like someone who's mad about something, then you sprinkle in a bit of intelligence and then you sometimes just get things wrong. Anyone can be an armchair quarterback. For us in the trenches doing this stuff, we usually, at some point, say something is good enough. Sometimes just before race day.
I see you are doubling-down on the post length...
I doesn't sound like he cares? (sic) Are you a shrink? Dom has an interesting demeanor in his videos, but he has bothered to speak to me personally at length and we've had many in-depth email exchanges. Dom is smart. Really knowledgeable about Subaru engines! Eccentric perhaps? Most smart people are.
If you install the kit backwards it could wreak havoc. A "T" can influence the flow. A "Y" would be better, but a high quality running Y might increase costs.
Dom is the one that's worked on nuclear subs and designed and built Subaru engines for airplanes. Perhaps slow down a bit as you start to get inflamed by my comments?
Dom had sensors attached, which he collected data from AND also did shots with an infrared thermometer gun.
YES, it's 38% more more flow! That's huge.
You're forgiven for asking questions, but I don't get the attitude. You can be a twit with or without a degree.
Ah, yes. The infamous text tone. No anger or inflammation here. As a side note, I have been told by friends and family alike that I don't speak like normal people...haven't yet figure out what that means.

He's smart. I never said he wasn't. I have presented a few "what if" with the limited amount of data he's presented so far, but I have some level of confidence that he is reasonably competent in this field. After all, he has presented us with some very interesting stuff. As my vocation isn't specifically Subaru engines, I can say I never would of thought of it. But just because he owns a shop and has a cool story (and I may or may not) doesn't mean he's explored all angles. Engineers are constantly working on improvements. It's why technology is where it's at today. But I get it. Criticism is a hard pill to swallow. Nobody likes being told they may be been able to improve, especially when knowing ones qualifications are a big deal to some.

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If you just purchased the mod recently, check to see if you got one with the hose clamp on the fitting side that goes to the block Instead of the crimp clamp, it makes it so much easier to install, You’ll need a 1” deep socket!
 
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