Coolant Not Recirculating Correctly Between Lower & Upper Reservoir Tanks

[chuglobal]

I've been watching this since January. I use to have an 02 WRX and now I have an 04 STI. I replaced my STI OEM radiator back in January w/ the GMS Radiator and noticed something very interesting since the install. In both my WRX and STI (before the radiator replacement), the lower reservoir tank use to increase in coolant when hot and decrease by about the same amount once the coolant/system cools. However, since the install of the GMS Radiator ... I noticed that the lower reservoir tank would always have a net increase in coolant even after the system cools; I also noticed that the upper reservoir tank coolant also seems to decrease. I'm assuming the coolant is not recirculating out of the lower reservoir tank back into the upper reservoir tank even after the system cools. I do have the STI radiator cap on the upper reservoir tank and the OEM GMS radiator cap if that really makes any difference. So here are my questions:

1. What is the pressure/PSI rating of both the Subaru OEM radiator caps: upper reservoir tank and OEM radiator?

2. What could be causing the issue?

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[Uncle Scotty]

ya gonna want the oem caps

[chuglobal]

How would the OEM vs. STI radiator caps make a difference except in pressure ratings? Also, the GMS Radiator uses a universal radiator cap unlike the proprietary cap on the OEM radiator, I assume in a good way. I could technically replace the upper reservoir tank cap w/ an OEM cap however I would still need another universal cap for the GMS radiator.

I'm doing a test ... I picked up another STI cap so technically I have an STI radiator cap now on the upper reservoir tanks and GMS radiator; I wonder if this might address the issue?

[Uncle Scotty]

d000000000000d........ya gotta have one that is less than the other by the same amount that the factory ones are different

they are that way on purpose

****ing with that isnt good

[chuglobal]

Do you know or where I can find the OEM radiator caps (upper reservoir tank and radiator) pressure ratings besides just walking into a local Subaru dealer? Interesting ... then why would Subaru offer the STI cap; that would make the difference between the OEM caps greater?

[munkis]

The cap on the upper tank is a pressure cap. The one of the rad is a NON-pressure cap. Use the OEM non-pressure cap on the rad.

[chuglobal]

I don't think the OEM non-pressured radiator cap will fit the GMS radiator, I will have to check again.

[munkis]

Then make a non pressure cap by hacking out the valve in the generic one, all you need to keep is the top part and the seal, all that should be left is the little bell.

[MAJRMSA]

Originally Posted by chuglobal

I don't think the OEM non-pressured radiator cap will fit the GMS radiator, I will have to check again.

Yes it does, I have a GMS Radiator with an oem cap.

[chuglobal]

Got it ... I now have another thing on my to-do list.

[rick-l]

Do you think you have an air leak in the hoses that go to the resevoir bottle?

[chuglobal]

I will need to check the hoses that connect the metal black pipe to the lower reservoir tank and to the radiator cap on top of the radiator.

[chuglobal]

Quick update ... I've been using the STI radiator caps on both the lower and upper reservoir tanks over the last 3 weeks and everything seems fine. Coolant increases when hot and decreases when cold in the lower reservoir tank.

[666stars]

higher pressure cap goes on radiator, lower pressure cap goes on turbo coolant tank

the lower stock cap is 20psi, the sti cap is 18.85 psi