Hi Everyone,

I have an subaru EJ20 turbo engine that I'm working on getting into my car. Right now the main project is getting the coolant lines back into the engine compartment. I've made it that far and will be reinstalling the engine to hook up the cooling to the engine. However, my question comes from my potential (mis)understanding of how the cooling system should work. My question is about the two ports on the side of the water pump. I believe these are used for the heating system in the original car. All the fittings on the water pump are used as a bypass for the cooling system when the thermostat is closed. Does this sound correct?

Since my car won't have heat, I still need some type of bypass for when the thermostat is closed. What I'd like to know is if my potential idea will even work. My idea, is to leave 1 of the ports on the water pump plugged. And use the other as a return from the Turbo. What I'm hoping would happen, is the water pump would pump coolant to the oil filter/oil cooler, then from the oil filter/cooler the coolant would go the turbo bearing. Once the coolant reaches the turbo bearing outlet, it would go into the small tank on top of the engine. The tank has an outlet on the bottom which I was planning to route to one of the ports on side of the water pump.

Would this even work as a bypass or am I completely off on how to get the cooling system to work? Previously there was a port that came off the back coolant cross-over tube which is now blocked and is being used for the water temperature sensor location. I think this is where the small tank drained coolant back into the system. I think that off those 2 ports on the water pump, that I plugged for now, were some hard lines that went towards the top of the engine and then fed into the heat core.

Thank you for your help!

Water pump ports with plugs


Turbo Outlet


Small coolant tank on top of engine


Another pic of the coolant tank on top of engine

Also there should be small coolant lines that tee off the heater core circuit to the throttle body. If the engine was stock as it was pulled from the car you would loop together the lines that would have gone to the heater core. I don't know enough to give an opinion on your idea, I have always just stuck with the factory coolant configuration.

Not sure exactly which EJ20 engine you're using, mine's an EJ20K so there may be subtle differences.

On my engine the turbo is fed coolant from a port on the passenger side head, it exits the turbo and goes to the large port on the top of the water tank. The water tank then has a line that goes down under the intake manifold, across the block, and down into the water pump/thermostat housing

The thermostat housing on mine has 3 ports on it:
Return from the heater core/throttle body.
Inlet from the water tank.
Return from the oil cooler.

I ended up looping the heater core out, but I had a problem with air bubbles getting trapped in that loop whenever I drained/refilled the system, making it very difficult to bleed, so I also installed a tee fitting in the heater core loop.



From there I ran a hose over to the water tank and teed into the small port on top that connects to the radiator bleeder port.



The engine should have a spot for 2 different water temp sensors, one for the ECU itself, and a separate one for the gauge. My memory's a bit fuzzy on the location but I believe there's already a tapped hole on the crossover tube for a gauge temp sensor.