Subaru WRX Cooling System Upgrade

This article brought to you by the “EJ’s Boxing Club” t-shirt (link opens in new window). One for the Subaru fan.

Overhauling your cooling system is an often overlooked and unsexy way to give your engine a little more room to stretch its legs power-wise. In my quest to fully round out my WRX as a well-sorted sportscar, I installed a Ron Davis aluminum radiator and a Crucial Racing “Coolsafe” thermostat. Read on for the full radiator and thermostat swap guide in newbie walk-through format.

Tools Needed

  • 10mm long socket
  • 12mm socket
  • Standard ratchet or ratcheting air tool and compressor
  • Needlenose pliers
  • Torque wrench (you don’t have one STILL? BUY ONE.)
  • Ramps or jack and jack stands
  • Wheel chocks
  • Funnel

Supplies Needed

  • 3+ gallon drain/catch pan
  • A roll or two of paper towels
  • 1 gallon of Subaru coolant (buy 2 if you’re not using water below)
  • 1 gallon of distilled water (omit this if you bought 2 above)
  • 1 container of Subaru Coolant System Conditioner (now recommended by Subaru for all coolant mixtures)
  • 4 new hose clamps (I bought OEM Subaru ones)
  • Optional but highly recommended: Latex or Nitril medical/surgical gloves
  • Your stock radiator assembly uses screws to hold the fans and overflow tank pipe to the top of the radiator. If your new radiator is threaded for bolts (most likely), and not screws, make sure you have 5 of them, as that is what you will need for a proper install.


This install was not at all hard. If you have the supplies and tools above, it should take you around 3 hours maximum if it is your first time doing it. However, I always recommend giving yourself extra time to do the work without hurrying for any reason (dinner plans in 3 hours, daylight ending soon…). It is also always a good idea when doing anything like this to have a backup means of transportation in case you need to go to a hardware store.

Be SAFE. Coolant is nasty stuff. Do NOT get it in your eyes or mouth and do NOT pour it down the drain. Catch your coolant, when the time is right, in your drain/catch pan and then funnel it into milk jugs or other bottles to take to your local automotive store for proper disposal. I’ve been told that some locations allow the dumping of coolant into drains because their water treatment facilities allow for it. If you plan to go that route, you absolutely should contact your local water/sewage treatment folks and find out ahead of time.

Let your car cool before doing this work. Never remove the coolant reservoir cap unless your radiator’s top tank is nearly cool to the touch. Note that I didn’t say “it’s okay if it’s pretty warm, but not hot”.

I have done my best to make this a very thorough and detailed article for even the most novice mechanic. All references to left and right are in relation to standing in front of your front grill looking into the engine bay.

Step 1: Get the coolant draining

  1. Lift the front end of the car, either by driving up on your ramps or jacking the front end up and securing jack stands. Put wheel chocks behind the back wheels. I happen to have a set of homemade mini-ramps that I use to lift the car off the ground enough to jack it up. For this job, I did not jack the car up, but rode the car up onto the mini-ramps and left it there with wheel chocks behind the rear wheels. My mini-ramps are about 3-4″ high. This is pretty ideal for this job because you can get under the front but you don’t have the front end way up in the air. The lower the front end, the more coolant you will get out of the engine block, and a full coolant flush is one of my goals.
  2. Remove the black plastic undertray from the car. Set it and its bolts out of the way.
  3. If you still have the stock intake duct that feeds cold air from the front of the car into the fender well, remove that from the car. It is 2 bolts which I believe are 12mm.
  4. Unplug the two fan connectors as seen in the pictures below. Ignore the fact that I happened to take these pictures later in the process than you currently are. The female sockets have a tab that needs to be lifted up while pulling (gently) on the male portion of the plug. I unplugged both of these without getting under the car. It was a bit of contortion, but it can be done in a few minutes.
  5. Standing in front of your engine bay, look at the left top area of your radiator. You will see a small hose clamped to a stem. The hose leads to the black coolant reservoir. Using your pair of needlenose pliers, squeeze the hose clamp at the radiator and slide it down the hose 2 inches or so. Do not detach the hose from the radiator yet.

  6. Look straight down from the stem you just were working at. Place your drain/catch pan under the car in the area where you are working.
  7. You are going to (not yet!) remove that hose attached to the stem and a few ounces (perhaps 10-20) of coolant will come out. If you’re particular about making messes, do what I did in these pictures and make a runway for the coolant that directs it right into the pan.
  8. Alright, go ahead and pull off that small hose and aim it downward. Let it drain.
  9. While you’re at it, slide the hose clamp down and pull off the other small hose that attaches to the left side of the black hard line going over to the coolant overflow tank (white plastic). Let it drain as well.
  10. While draining still, remove your coolant reservoir cap.


  1. VoltesV
    Posted October 7, 2007 at 11:05 am | Permalink

    Hey man great write-up! Good thing I found this before starting the same job this weekend. Looks like we have the same radiator (Fluidyne), what size bolts do I need to for this installation? I’m replacing my radiator with the Fluidyne since the stock one leaked.

    NASIOC User Name: VoltesV


  2. Jon
    Posted January 22, 2008 at 12:57 am | Permalink

    Great write up! I have upgraded my TS radiator to a WRX radiator. One thing about Subaru is the fan starts at only 95oC which could be a bit late. Also the thermostat opens at 80+oC and is partially opened even at 95oC.

    I have replaced the original thermstat using an equivalent one used on a Renault. It opens very early at 70oC and is fully opened at hot. This enhance the water flow and provides better cooling.

    The engine now runs much cooler , more stable and provides more torque even on a very hot day. If you are going to get your hands dirty, do consider replacing the thermostat.

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