The engine on my car has the option from the factory for what they call oil-to-air heat exchanger.
I like to call it, more simple: oil radiator.
I choose to call it oil radiator because I want to differentiate it from the oil-to-coolant heat exchanger, commonly known as oil cooler.
With the oil radiator option, the oil cooler is deleted and the respective connection to the water pump is deleted too. The water pump replacement becomes the same water pump as a GRB WRX (non Sti).
The oil radiator looks like this:
There is a replacement radiator that is suitable to be run in place of the OEM.
Remember, never install a used radiator on your engine, just as you would not install a used cooler.
The replacement I speak of is here:
It comes with 4 mounting tabs for auxiliary cooling fan.
Turn it around, so that the tabs face the engine.
Use the bottom two tabs to mount it to the bottom radiator support. they will match to pre-existing holes there.
The way i used those is:
The holes are large diameter, to where you could slide in the screw head, then you slot the head of the screw to the side of the hole until it becomes captive.
I put some rubber pieces under the rad.
As you tighten the nut, it fastens against the rubber pieces the rad sits on.
Then for the top of the rad, you use the top mounting tabs with a piece of aluminum flashing from Home Depot, and you mount it to the top radiator support. There I also used a rubber washer under a regular washer. I made the rubber washer out of a piece of rubber.
Now this rad is securely mounted and vibration dampened.
It fits like it was meant to be there, because the provision was always there.
This rad has NPT threads for the fittings.
You buy brass NPT 1/2" to I think 3/8" barb , 90 degree angle fittings from Grainger.
These extend to the exact length that the original ones did. I've measured this combo with the original rad and they're basically identical.
Then, you should go to japanparts.com, to look at all the components of this system, to see what else you need. There are 4 hoses and one conduit riser. I had the conduit riser, but that's not a fortune.
You have to get new hoses, because the danger is there, even if you have a small crack in your existing ones. Also watch for a TSB in which they give you double clamps for all those hoses. Also, position the clamps per the marks on the hose and group them with the spring clamp outwards and the worm clamp inwards. Tighten the worm clamp to where it cannot go past the hose barb on the conduit riser, for safety.
Maybe we should not call these 4 "oil hoses". Let's call them "special rubber couplers". This gives you the idea of never attempting to substitute them with some rubber hose that you may have laying around.
The factory special rubber cuplers are rated for the oil contact, for the oil temperature and for the temperature of the environment where they live, by the headers...
They also have marks on them for the position of the clamps.
One reason to be this careful is because of the temperatures. Another is because of the pressures. Cold oil pressures by the hose can get to 100 PSI. A clamp can hold 120 PSI. Two clamps in series increase this, but I was unable to find calculations so I can estimate by how much.
Since clamps are all about friction, increasing fricition area to double, should have a significant effect.
The problem is also that a worm clamp loosens with temperature. There are special worm clamps that don't do this and they don't cost a fortune either..
The spring clamp does not loosen with themperature, at least not by a significant amount. This is why the pair of them are probably chosen by the factory.
Of course, they could have installed braided stainless tubes, for this connection.
However, what is one of those? It's a tube made of a material similar with Teflon, covered by a braid.
The braid prevents one from seeing defects in the tube as they form, such as bubbles, discoloration, etc.
By the time it fails, one has no clue it was abbout to fail. Hydraulic hoses burst all the time, as people in the industry know. And many times they don't carry the kind of heat that these special rubber couplers do.
This is why I think the factory chose them.
I have a trustworthy oil temperature gauge and on a hot day, with slow traffic driving, my oil temperature goes up to 210F, with this radiator. This is with Castrol 5W50.