Radiator Swap in your GC

Radiator Swap in your GC

Jul 1, '21

In this blog post we talk about the radiator in your swapped car. We’re specifically talking about GC chassis (93-01 Subaru), but you would use similar information for all radiator swaps.


When doing a swap in a GC chassis, there will most likely be a radiator upgrade as well. which is typically an aftermarket radiator for a GD application since there are not many GC options. When going this route, the key is getting a slim fan and thinner radiator due to the shorter engine bay of the GC compared to the GD. If the radiator is too large or if stock fans are used, it may not fit. We generally recommend a Koyo radiator and using the iWire GC to GD Radiator Shroud to keep the mounting simple and you don’t have to put holes your core support or worse yet use zipties.


The radiators from a GD chassis (02-07 Subaru) are a great upgrade because of the way the coolant passes through the core. When upgrading to a GD radiator, the GC fans will not mount to it so we recommend getting 12 inch slim fans like Spal or Flex-A-Light. These aftermarket fans will mount to the radiator with a little hardware kit that are special zip ties.


The biggest tip we can give when doing a radiator swap is BUY A GOOD SLIM FAN! Decent quality aftermarket radiator will do most of the work and then you just want to make sure you have good slim fans. When it’s hot and stuck in traffic and the car is not moving, that’s when you need your radiator fans to do their job. We see this issue more commonly with the GC radiators with slim fans and have come up with a potential solution. Check out this blog for more info.


Once everything is mounted mechanically and the hoses are routed, you’ll have to make the wiring changes since the connectors on the radiator will no longer match the connectors on your wiring harness in the car.


Wiring Info:



All GC’s have a 2 wire connector coming from the harness. The notes below are in reference to the connector coming from the new radiator fan wiring connecting to a non turbo model with only 2 wires. The reason there are multiple wires is that the Turbo models (IE a WRX) have high low and high settings where both fans are activate while NA models (IE a GC) only an on and off setting with a primary and sub fan working independently. This is built into the fusebox of the car and can't be changed. With the fixes mentioned above this is not an issue.


2 Wire connector from new radiator fan: just match up the power and the ground from the stock harness to the radiator harness.


3 Wire connector from new radiator fan: combine the two power wires into one joint with the single power wire from the harness and you’ll combine the single ground wires together.


4 Wire connector from new radiator fan: combine 2 powers and 2 grounds into the single power and ground wire coming from the GC.


Newer model cars: Shouldn’t be an issue. 02-03 WRX with a 04+ radiator with fans, you would connect the wiring as mentioned above.


Using a GC Radiator with a turbo swap - If you happen to use a GC Radiator this is how you would connect the overflow lines. The upper reservoir line coming out near the turbo should go to the cap on the radiator (Red). The line coming from under the cap on the upper reservoir should go to your overflow (Blue).

2022 update on radiator caps. Although using caps of the same pressure has worked well for us up to this point, we've gotten some more insight that's to our friends at Flatirons Tuning. The theory is that unless you use the factory 1-way pressure cap on the radiator side you should use a higher pressure cap on the radiator side so that pressure is only relieved by the upper tank unless there is a serious issue in which case the radiator cap can bleed off. More about radiator caps can be found by clicking here. If you try running the higher pressure cap on the radiator, keep an eye on it and let us know if it works for you.


Watch this video of our radiator fan wiring changes on Bucky Lasek’s RS Weekend Swap.

Watch Bucky’s video to see how to handle the radiator mounting and hoses:
Here is another video of the OG RSTi Koyo Radiator Install
Radiator Connectors: