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Discussion Starter · #1 ·
Ok so here's a little puzzle. For the longest time since I've installed this rad I've had a leak on the passenger side where this filler neck is. Being that the 02 wrx already has a filler neck for the cooling system I bought another radiator cap to cover the new neck on the radiator. If the car is driven lightly it doesn't seem to leak but hitting boost and 5,000+ rpm is when I see coolant in this area. It was never a huge issue until I fixed my boost leak bur now it seems there is enough pressure in the cooling system that it leaks more from all the pressure. Is it possible the radiator cap valve is opening under pressure shooting fluid through the filler neck return line on the radiator? That's what it looks like but then again I could be wrong. Anybody got any ideas on what it could be and a solution?
 

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The pressure in your cooling system is something like 16ish psi at temperature. When. You start bashing on it the excess heat is absorbed by the coolant and it expands. There may be a super tiny leak that is exaggerated when the system starts dealing with the higher temp and pressure coolant.

I would pressure test the system and listen for air around the leak. Check any hoses including the one for the overflow.

Sent from my SAMSUNG-SM-G935A using Tapatalk
 

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Discussion Starter · #4 ·
The pressure in your cooling system is something like 16ish psi at temperature. When. You start bashing on it the excess heat is absorbed by the coolant and it expands. There may be a super tiny leak that is exaggerated when the system starts dealing with the higher temp and pressure coolant.

I would pressure test the system and listen for air around the leak. Check any hoses including the one for the overflow.

Sent from my SAMSUNG-SM-G935A using Tapatalk

Unfortunately I don't have access to a Tester to pressure test the system. Any way way to rig up a way or check it a different way?
 

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Wait.

Did you TEE the TWO overflow lines together?

Why is there NO overflow line coming out the rad cap on the rad itself?

(OK so I did think this is a prank -- good one if it is).
 

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Wait.

Did you TEE the TWO overflow lines together?

Why is there NO overflow line coming out the rad cap on the rad itself?

(OK so I did think this is a prank -- good one if it is).
I completely missed that, there isn't a line back to the overflow. That's your problem, and you probably have a ton of air in the system

Sent from my SAMSUNG-SM-G935A using Tapatalk
 

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I'll leave the thread open because if it's a prank, it's funny, and if it's not a prank, the solution is simple: tee the lines and bleed the system thoroughly.

EDIT: An interesting idea: Use the stock rad cap on the turbo overflow reservoir, and see if you can find a rad cap rated at 2 bar or higher (I doubt you could?) and use that on the rad itself. It should prevent the rad cap on the rad from opening since you'd need over 1 additional atmosphere of pressure in the system above the opening point of the cap on the turbo reservoir.

BTW, Koyo sold an OEM style rad without a cap opening; I have one on my car. Nice rad.

Or... tee the lines...
 
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