Project BRZ, Oil Heat Exchanger Installation

More track day prep here. One of the common issues with the Toybaru Twins is that the oil temps are pretty high, so in an attempt to control it, I installed an oil-coolant heat exchanger.

I’m not really breaking any ground here, since this exact cooler was factory fitted to the second gen BRZ/86, and others have fitted it to their first gens, but since no first gen got any sort of oil cooler from the factory I figured this was a good compromise for what I’m doing.

Yes, ideally you would fit a proper oil-air cooler in the front with a thermostat, but 90% of my use is on the road, where it wouldn’t be needed, and one major benefit of the heat exchanger for me is that because it sheds oil heat into the coolant, it can also suck that heat from the coolant, which is much quicker than oil to heat up, to bring the oil up to temp quicker when it’s cold.

Cusco even released their own version of the heat exchanger for the first gen, which was a little more in-depth and required tapping into the actual radiator hoses.

The basic theory is that the heat exchanger sits under the oil filter, and has coolant circulating through the inside of a copper core as the oil goes around the outside of the core. It’s quite a nice looking unit. Genuine Subaru, of course.

This is where it goes, under the oil filter.

And this loop under the throttle body is where others have tapped into the cooling system, and where I will too

I purchase a meter of 5/16″ / 8mm coolant hose and used some spring clamps to fit it to the exchanger. Half a meter on each side is more than enough and will need trimming to fit nicely.

I removed the filter, which was way too tight, and then had to go out and buy a deep 24mm socket in order to remove the old threaded stub, as this needs to be replaced with a longer one

Slightly longer

The exchanger comes with a new O-ring already, it just needs a smear of lube before fitting

Clean up the housing, since you won’t be able to access it again. Make sure the small indent on the right is clear of debris too, as the locating tang on the exchanger needs to fit in there

Thread the hoses through under the AC compressor first, and then offer up the exchanger. Once it’s sitting nicely, slide the centre stub through and tighten to spec (45NM)

Oil up the seal on the new genuine filter and fit that too, Hand tight, no uggas or duggas.

And now you can see what It’s going to look like

Now it’s time to connect up the coolant side of it

I removed the loop that is there from factory. Nothing came out of the top pipe, but a small amount come out of the lower one and proceeded to go everywhere, so I quickly measured, cut and clamped the hose on

The top hose was measured, cut and fit too. I don’t know if it matters which way the coolant circulates through the cooler, in my research from others doing this the consensus was that as long as it was flowing through, that’s what mattered.

I took the opportunity to change the oil too. According to the sticker, it was changed just before I got the car with Valvoline 5W30 (which is fine oil). Oil pressure was good, but I was surprised at how dark the oil was in just two thousand km or so. After much research, going over all the relative viscosities of oils at certain temperatures, I settled on Castrol Edge 5W30 as my oil of choice. It’s thicker than the stock 0W20, but Subaru did recommend 5W30 for extreme use cases (like track days), and I don’t want a thin oil breaking down on the track and costing me an engine.

Once everything is buttoned up again, the fresh oil is in the sump and the coolant has been topped up, start the car and at idle with the heater turned to hot, slowly open the bleeder on the heater hoses near the firewall until coolant comes out of it. This should be enough to bleed the air out, but keep an eye on coolant temps for a couple of drives just in case.

So far the results are promising. Previously, I was regularly seeing oil temps 10+ degrees C above coolant temp when at operating temperature, which would often mean oil temps 100+C.

Now I’m seeing oil temps much closer to coolant temp, within a couple of degrees

The oil temps also drop back quicker than they did before after a hard run, and the time for the oil to come up to temp on a near zero C cold winters morning is significantly quicker, maybe even halving the time.

As a bonus, it appears I have picked up a couple of PSI oil pressure at operating temp, too. I was sitting around 10-12PSI at idle previously, now it’s 14-16PSI.

Over all, considering it cost about a quarter of a decent oil cooler kit, and unlike those it also helps bring the oil to temp, at the moment at least, I am happy with the setup. The big test will be at the end of the month when I take the car on the track. Hopefully it can keep the temps under control.

Parts Used

Subaru 21311AA220 – Cooler Assy Oil
Subaru 21317AA070 – Connector Oil Cooler
Subaru 15208AA130 – Oil Filter
Subaru 803916010 – Sump Washer
1 Meter 5/16″ or 8MM Coolant Hose

Please note these parts are specific to my car and may vary. Please check before ordering.