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Old 02-29-2012, 03:49 PM   #1
Jubert39
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2004 AW Subaru WRX
JDM v7 STI spec-C

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I just purchased a koyo all aluminum radiator for my 04 wrx (sti swap). I was doing research and i guess radiator caps are important. So after readin quite a bit, i know there are 2 radiator caps. (1 for the top reservoir tank, amd 1 right by the top of the radiator)

Couple questions:

1) i read the sti top radiator cap (on the reservoir tank) is 1.08 bar and he lower radiator cap is 1.3 bar. Is this accurate? If so, is this true for the wrx (2004) models as well? I have an ej207 complete engine swap, and the top coolant resevoir tank is from that sti engine, so is that the same as the usdm cap?
2) should i get a 1.3bar lower radiator cap? I read that this cap must be greater than the top cap b/c u want the top to be able to vent under pressure.
3) if i do need a 1.3bar, oem sti efficient for koyo aluminum? Or should i look at aftermarket.
Thanks
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Old 02-29-2012, 04:34 PM   #2
Rally Monkey
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"u want the top to be able to vent under pressure"

You do not want venting through any cap. Venting is done through the overflow tank next to the radiator. There are caps with higher pressure ratings, I would not be concerned about that, get new caps with good seals that fit. OEM is fine.
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Old 02-29-2012, 04:51 PM   #3
Jubert39
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JDM v7 STI spec-C

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Quote:
Originally Posted by Rally Monkey
"u want the top to be able to vent under pressure"

You do not want venting through any cap. Venting is done through the overflow tank next to the radiator. There are caps with higher pressure ratings, I would not be concerned about that, get new caps with good seals that fit. OEM is fine.
Are the wrx and sti the same tho? Can i just reuse my wrx lower rad cap or shld i get a new sti one (if they are diff pressures)?
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Old 02-29-2012, 04:59 PM   #4
Rally Monkey
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You can use the old one, no problem.
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Old 02-29-2012, 05:00 PM   #5
Bacon117
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Quote:
Originally Posted by Rally Monkey View Post
"u want the top to be able to vent under pressure"

You do not want venting through any cap. Venting is done through the overflow tank next to the radiator. There are caps with higher pressure ratings, I would not be concerned about that, get new caps with good seals that fit. OEM is fine.
The cap venting under pressure is what allows the coolant to go into the water tank.

Pressure ratings are quite important. The higher the pressure rating, the hotter the coolant can get before it boils. But you don't want it too high that it causes other problems. Stick with stock pressure to be sure.
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Old 02-29-2012, 05:02 PM   #6
Jubert39
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So long story short- when i put the koyo radiator in, just reuse my stock oem wrx radiator cap?

Thanks for the help guys.
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Old 02-29-2012, 05:35 PM   #7
Rally Monkey
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Quote:
Originally Posted by Bacon117 View Post
The cap venting under pressure is what allows the coolant to go into the water tank.

Pressure ratings are quite important. The higher the pressure rating, the hotter the coolant can get before it boils. But you don't want it too high that it causes other problems. Stick with stock pressure to be sure.
Yes, I got caught up in semantics on that.

You can use the stock cap. Koyo also makes a racing cap they recommend for that radiator because it hold more pressure and better utilizes the cooling efficiency of the large radiator.
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Old 02-29-2012, 07:42 PM   #8
Jubert39
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JDM v7 STI spec-C

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Thanks folks! Looks like I'll just reuse my 04 wrx radiator cap. Saves me some money
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