A huge thanks to Bob and Art, who have both provided me with a lot more information on how the coolant system works and have given me good leads to follow.

A phone call from Art gave me some really good insight on how the Subaru cooling system works. What' I'm used to is American V8s where the thermostat is on top of the block where the water exits to return to the radiator That way when the block heats up, the thermostat opens, and the pump can now push water to the radiator. With Subaru having the thermostat on the inlet there is a need to push hot water from the top of the block where combustion is happening to the thermostat housing to get that warm and opening up to let the pump pull cool water in.

Let me take an aside right to say as an engineer who studied fluid flow and thermodynamics, I think having the thermostat on the inlet is an absolute asinine idea. It leaves no way to really circulate water through the block or heater core to help everything warm up. With the inlet of the pump blocked off, you are left to almost completely to conductive heat transfer to warm everything up. If you have the inlet open, but the outlet block off, but have a bypass around the thermostat that loops back into the block, then you can at least pump the water around the block so that it gets hot via convective heat transfer rather than waiting on conductive. #ENDofRANT


As Bob pointed out hot water to the thermostat can come from 3 places

1) The Degas tank (Mine is hooked into the bottom of the degas tank)
2) The Oil Filter Block
3) The heater core.

As you will be able to see in the attached diagram, I believe I have all 3 hooked up properly, but I'm still not getting hot water to the thermostat, I have some thoughts on each one:

1) Degas Tank - Even though I used a vacuum system to fill my entire coolant system, when I opened the cap of the degas tank this morning it is full of air, no liquid at all. When I put the vacuum system on it water quickly comes up into the tanks and gets spewed out the vacuum exit. Once I shut the vacuum off the coolant recedes. My degas tank has 3 lines, one out of the bottom to the thermostat housing, 1 on the top from Wayne's mod, and one on the top to the turbo. It seems like I'm not going to get hot water from the degas tank to the thermostat unless the water gets hot enough to expand through the Turbo line or Wayne's mod line, and then drain back down the bottom of the degas tank to the thermostat. Doesn't seem like this is happening.

2) The oil filler Block - I remove the actual block from the oil filter, but I just jumped a rubber hose where it used to be, so this is functions as stock. This line is at the bottom of the engine and I'm not sure how quickly the water down there heats up waiting on conductive heat transfer.

3) This is the only way i can see that the engine should be able to properly heat up, but I guess it depends on how the inside of the block is setup with water flow. The return from the heater core goes between the thermostat and the inlet of the pump. So in theory, the pump should be able to push water into the heater core and back to block, this would allow some convective heat transfer to warm up the water in the block. I have a 4 way heater valve, so even with the valve closed water will still circulate through it and back to the block.

I'm really kind of stumped here, this is a crappy setup, but it works in a stock car so I can't figure out why it won't work for me. The only thing I can see that is probably different from the stock setup is that line from Wayne's mod to the top of the degas tank, I'm not sure what used to feed the degas tank on that port.

I'm tempted to remove the stock thermostat, place one inline on the outlet of the block, and have a T right before the block that feeds back to the stock thermostat housing.


Cooling Diagram.png

Degas tank.jpg

Radiator.jpg