This is one of the easiest DIY maintenance things you can do your Subaru. I believe the dealership wanted to charge me $495 to do it. To DIY its about ~$40 in OEM coolant (from the dealership) and $30 in parts/tools. You could probably get by without the special funnel but it makes ‘bleeding’ the system more straightforward.

Like the CVT Fluid change, I did a lot of research and consolidated it into a list of steps then had ChatGPT organize it into a printable procedure PDF.

Coolant flush instructions that I followed

Tools and Supplies

Item Notes
Subaru Super Coolant premix 3 gallons
Subaru Cooling System Conditioner 1 bottle
Radiator drain plug O-ring If replacing
Spill-free coolant funnel kit
Large drain pan
Rags / paper towels
Flat or Phillips screwdriver For splash shield clips as needed
10mm socket For undertray / access panels as needed
Pliers For hose clamps if pulling a hose instead of using the radiator drain
Jack, jack stands, or ramps
Wheel chocks
Gloves and eye protection

Specs
Coolant type Subaru Super Coolant premixed (blue)
System capacity ~7.4 qt

Supplies

This service really only requires the coolant. All my research pointed me towards: “Only use OEM Subaru Super Coolant premix.” I’m not sure how much it actually matters but its pretty cheap and with the amount I am saving doing it myself, I might as well use quality OEM coolant.

Another thing to note is that the Subaru dealership parts guy said I’d only need 2 (gallon) jugs of coolant and I wouldn’t use up the 2nd one. (He was right!)

I didnt end up getting the coolant conditioner. Based on my research it was recommended for the generations with headgasket issues, but no official Subaru service bulletin recommended or recall required it for my generation or model of engine.

While technically optional, I highly recommend the Harbor Freight No-Spill Radiator funnel kit https://www.harborfreight.com/no-spill-radiator-funnel-kit-58423.html . I’ve only ever done it with this kit, but I can’t imagine doing it without. It seems like it would be much messier and take longer.

Coolant jugs and funnel kit

Draining the Old Coolant

You want to jack up the front of your car or put it on ramps to get to the drain. It also helps bleed the air later when you refill.

Car up on ramps

Drain pan under car

I’d make a terrible influence because I didn’t get enough pictures of the process but the drain plug is dead simple to get to once you take off the plastic shielding–which is held on my a dozen plastic plugs and a handful of 10mm bolts.

The drain plug is literally a hand tight plastic piece that you can unscrew by hand (and reinstall by hand when you are done.

It takes a few minutes to full drain. While this is happening, most people recommend taking off the resevoir and cleaning it out. So thats what I did. Again, no pictures of this process because I’m bad at making content. Its easy to take off though. One 10mm bolt and it basically sits in a slot that you have to wiggle to get it out.

Flushing

So, I didn’t have time or inclination to “flush” the system. There was no real reason I had to flush it. There was no contamination, it never over heated, etc. Since this was for general maintenance purposes I just drained and refilled.

Refill

Refilling was super easy with the no-spill funnel. You just attach it and fill it up. Once it “settles” you start the car and let it bleed the air out. You ideally want two cycles of the thermostat so it can take some time.

If the coolant gets low in the funnel, refill it.

Coolant bubbling as air bleeds out

It bubbles quite a bit at first then slows down. It helps if you get the top radiator hose a slight squeeze every so often to help move air out.

Engine temp after two thermostat cycles

As you can see, I got the engine up to temp. Note how long it was running though. The whole service was super straightforward but it took an hour an a half mostly because the engine took so long to heat up.

Almost finished — bubbling slowed down

Once its stopped bubbling you will have a bit of coolant in the funnel. Take it off, and pour it into the resevoir until it reads “Full”.

Wrap-Up

Old coolant drained out

I poured the old coolant back into some old 1 gallon water jugs I had and took them to a local auto parts store to dump (most do it for free).

Thats it. I took it on a test drive up the George Washington Parkway and monitored the temps. Everything looked good!