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Old 02-15-2012, 10:59 AM   #1
Scooby Specialist
Member#: 159743
Join Date: Sep 2007
Location: Plymouth Ma
07 STI Limited
TurboMike Tuned 2.35

Default Subaru how to make an Upper Thermostat Housing Setup

So I have been reading a lot of posts lately, uncommon for me, but most from Team Scream. He has shared some of his most private data on how to, in the most scrutinized way, build a subaru motor. Its not my first time around the block but it was nice to see someone actually put some effort into explaining what was going on. Not to limit it to him Crystal, Fuji and some others have shared data that i just didn't have time for. Also limiting me was my biggest fear, the audience. I feel people are like NFL commentators on many forums. They look it over, sleep on it, and then say boy if Brady had of just... well you get the point. Overcoming these fears im releasing what i have been testing for over 3 years on all types of subarus, including but not limited to, Stock STI's, Stock WRX, Built, Sleeved, High HP, Low HP with the same results.

Ok enough about that junk here is my findings. The Stock Radiator system has been Picked apart as a great setup that heats up fast making it convenient for morning commuters especially in the north. As i came into the tuning portion with Turbo_Mike, the team at Romraider would release new features or access to different sections of the rom. At the time i was running with no maf and tuned it to run perfect, minus the CEL. However i was always limited to the cooling system. I was noticing in the summer even with the Koyo I couldn't reliably keep my subaru where i wanted for temp... There were work arounds, but why explain them when i have the following.

So you understand what you're about to see, think about a dodge pickup truck or a chevy or any small block v8. The cooling system consists of the same pieces, the Radiator, Thermostat, Hoses, either a fan clutch or electric fans to keep it cool and then stock or aftermarket fan control. Great.... However all these blocks use a thermostat at the top of the car. AFTER the thermostat gets heated by the engine fluids it opens. This allows your radiator system to cool it off and pump that cool water (At the bottom) back into the car. So I looked into this more. Our system works almost against us especially with good radiators and good fans. Essentially the more/better cooling items you get the harder it is to control the heat on the car. We essentially don't open the thermostat until the engine is hot and the radiator gets hot enough to heat the sucker up. What i was finding was the more i would try to control the fans by turning them on lower and putting better thermostats in the hotter it would get on the highway... Tracking may have different results as they have a massive amount of air going through the engine bay, however, 99% of us start it up, let it warm to the C or above and then drive it. End up 2 times plus a week in stop and go traffic and the fact that the line is in the middle somewhere floats our boat... Unfortunately im part of both of these. I get stuck in traffic but the fact that my car has a 170 thermostat and in the summer used to hover at 210 barely controllable was not cool.

So quick recap. Hot cars in the summer suck and we want to see something better out of the cars. K up to speed.

So i said heck why wouldn't i just take the whole thermostat out.... I read a little, Crawford and some other companies were in a debate at the time of why that's bad... I noticed i could control the temps perfect with the fans however the first 8F day out i realized why its not a good idea too... no heat for 60 miles and i thought i had frostbite... great...

Next i plotted why can't i have a thermostat in the upper radiator hose??? does something exist... At the time yes but it looked like garbage... Anyways i looked far and long and eventually came up with the following setup.

Upper thermostat housing and how to make one yourself.

This is a picture of it in my filthy car ATM... You will notice this nice shiny piece in between two Samco hoses. Please note that the Samco "type" hose is also required as the stock hose will exploded under extreme driving... did it in queens ny... living in ma... not a fun time.

So lets make this device now. What we have done is take your stock water pump and thermostat and cut out the internals of it. Why because the pump housing uses that gasket to keep it sealed, and if it doesn't i have found no ill effects from doing it this way (NFL Guys). this will allow water to flow freely in the bottom.

So you cut the internals out and put it back in your waterpump. I have this off a current car that im working on anyways so it was easy to take pictures.

Next you need to go to Jegs and get this awesome piece.
im not sure how much i can link so if you go to jegs and type the following in the search it comes up great. Ill put pictures below. (680-WN0072)

Next your gonna need a thermostat. Ive found good results with the following.

Mr. Gasket 4366

Its a 160 thermostat that fits and is supposed to be "high Flow"
Before installing you will see a floating metal Nipple is what i call it. i cut this off with tin snips to allow flow initially. (NEEDED) dont try to do it without... been there. When installing you will want to face the copper core towards your outlet from the engine to open properly.

Next just put it in the engine bay where its not going to hit anything and trim the hose accordingly. Obviously you will need 4 good clamps to hold everything together.

Last but most importantly... you need your tuner or someone locally with a tactrix cable to setup your fans to turn on "correctly" I find with a 160 thermostat i can hold temp (Always) at 170 with a - + 2 degrees. I say +- because on bugeye's or more specifically non AVCS motors they seem to generate less heat and can run down in the 167 range. Here are screen shots from Romraider which reads in Fahrenheit.

And what to change them to

Thats it. You change your hoses and put this in and your car now runs 170 degrees all the time. Here is a picture of another car with this setup working just fine.

What are the advantages of this system your going to ask. I find running a more consistent coolant temp runs the whole motor cooler and a more consistent Oil Pressure and Temp. We noticed a rise of 10-15 Psi Overall on the cars because of the cooler temps that Ive run it on. Also after a long highway runs the oil pressure is the same as the beginning. I've been running this setup on my de-stroked 2.3 motor for 99,975 miles now with no ill effects. through winters of -22F and summers of 110F in traffic. This setup might not be for everyone but for the enthusiast that doesn't like the car cruising at 167 and then in traffic at 205-210... this may be for you. Noticeable less wear on the oil from not cooking it all the time has been noticed too. Anyways, This is just a trick i thought i would share. Good luck and PM me with questions.
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Last edited by Bamofo; 02-15-2012 at 11:52 AM.
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Old 02-15-2012, 03:27 PM   #2
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region: Tri-State
Location: NY
2005 TickingTimeBomb
Jr tuned TT Sleeved


Nice write up man.
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Old 02-16-2019, 05:56 PM   #3
Scooby Specialist
Member#: 159743
Join Date: Sep 2007
Location: Plymouth Ma
07 STI Limited
TurboMike Tuned 2.35


still cant believe this got so few views.. I keep finding the new STI's getting way too hot and this fixes the problem.
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