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Old 08-24-2019, 07:44 AM   #1
Scooby Newbie
Member#: 489746
Join Date: Aug 2018
Impreza WRX STi Radiator Custom Shrouding

TLDR: My car is getting too hot and I'm looking to make custom shrouding around the radiator fans, radiator, FMIC, etc... What material (metal preferred) do you consider that is rather bendable to fit, easy to cut for different locations, and can withstand the heat and is corrosion resistant?

I have a 2016 Subaru WRX STI that is heavily modded (~20k+ to the engine alone). I have been noticing during hotter temps (95+ degrees) the coolant temps love to climb almost about as quick as the speedometer when doing any kind of spirited driving. I first noticed this issue (Jul 2018) when heading from San Diego, CA to Las Vegas, NV in 115 degree weather, in stop and go traffic with the AC on (because I love my AC). I took a glance down and noticed the temp gauge at 3/4 value, not in the red but surely not normal. I instantly killed the AC and rolled down the windows since I still had a 4+ hour drive ahead of me and didn't want to be stuck on the side of the road like many others. The whole way it was teetering from 215-230+ (If I didn't back off). To me, this shouldn't be the case as I've put the money into what I considered quality parts that should supposedly handle this type of weather.

Well one thing I never bothered with until right after that trip was a Koyorad radiator (It didn't help the issue one bit). Ever since then I've had it at my tuners shop and asked around A LOT about possible issues. All issues suggested (blown head gasket, cracked cylinder walls, warped heads, etc...) have given no suggestive symptoms (pushing fluid, white smoke in the exhaust, milky oil).

What I would consider the cars prime was literally racing 100 -130+ from Las Vegas back towards San Diego (~late 2016), I had an awesome fun run with some guy in an AMG... back and forth, not trying to win, just to enjoy the fun! This lasted for at least 2 hours with no issues such as this.

Now I can't even really get on it with any kind of 90+ degree temp without the coolant temp jumping to 220+ rather quickly. At those temperatures the car loves to shudder as though it's not getting enough fuel or something else. Obviously turning off the AC helps, but there was a point in a recent cross-country trip that I could do no more than 60mph up a grade with the AC off without the shuddering happening.

I do have a FMIC which I'm sure doesn't help with allowing air to get to the radiator. I have removed the under-carriage as that had appeared to assist with cooling. I still have a stock oil cooler, though I am waiting for a top-mount version from B-Line (as I'm about out of space for mounting solutions).

During my recent trip back home, my stop in Las Vegas helped, as I have a brother that's a master ASE mechanic with BMW there that helped me realize I had a damn radiator cap that was bad (specified for 108kpa, but couldn't event hold 90kpa). This did help some, but there is still an issue. After realizing the cap issue we did a pressure test on the coolant system. In about an hours time the pressure dropped, and we lost coolant somewhere. We don't know where as there were ZERO visible leaks. However, when we started the vehicle we noticed no white smoke, BUT noticed a massive coolant burning smell from under the hood. Still unsure what this could be.

Upon returning home to San Diego I had a compression test done to see if maybe... just maybe it would tell me something... It didn't as the cylinder pressures ranged from 144 -151.

While getting some services done after my ~7k+ mile trip my mechanic and I were talking about custom shrouding in and around the radiator to assist with directing airflow to/through the radiator. After looking at how the fans were mounted on the Koyorad radiator, I have to agree as there are so many gaps, it's not even funny. This finally brings me to my question.

I'm looking at creating some custom shrouding to assist with diverting the air where it needs to in the attempt to assist with cooling. I am considering doing this alone, though I have never done much true custom work (though I have the facilities and ability to figure it out).

If I was to make custom shrouding that would cover gaps between places such as the fans and the radiator, or between the radiator and FMIC, etc... what material would you recommend? I don't like to half-ass stuff, and as such I am considering metal shrouding (I just don't know what kind of metal, steel, aluminum, stainless steel, etc...). Some stuff that would be involved would be cutting and folding of the material to fit the design. What do you recommend?

For those that read it all, thanks and I look forward to your input!
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Last edited by Psycho-82; 08-24-2019 at 07:45 AM. Reason: Puncuation
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Old 08-27-2019, 12:25 AM   #2
Scooby Newbie
Member#: 441528
Join Date: Feb 2016
Location: Phoenix, AZ
2015 STI


I used posterboard for a pattern and then aluminum 050 sheet material on my 2015 sti. Thin enough to cut with good tin snips but strong. My next track day is Oct 5-6. My old shroud worked well but this one seals better.

Posterboard pattern

After test fitting I cut and bent my aluminum.

And assembled

Foam padding was placed on the flanges that meet the ac condenser.

After some paint

Last edited by phxsubaru; 09-06-2019 at 10:35 PM.
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Old 08-28-2019, 04:46 PM   #3
Scooby Specialist
Member#: 13530
Join Date: Dec 2001
Chapter/Region: NWIC
Location: Cascadia
EA63 , EA81T, EJ20G,


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Old 08-28-2019, 05:08 PM   #4
Scooby Newbie
Member#: 489746
Join Date: Aug 2018

Both of these are great info, thank you!
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