Why Upgrade Your Forester’s Intercooler?

Forced-induction engines, like the turbocharged motor in your Subaru Forester, compress incoming air to pack more oxygen into the combustion chamber. That compression generates significant heat, and hot air is less dense—meaning it contains fewer oxygen molecules for combustion. The stock intercooler is designed to handle factory power levels, but once you introduce engine management tuning, a higher-flow exhaust, or increased boost pressure, the factory unit can become a bottleneck. Charge air temperatures (CATs) rise, the engine’s electronic control unit (ECU) pulls timing to protect itself, and you leave usable horsepower on the table.

The TurboXS upgraded intercooler is a direct-fit, bar-and-plate intercooler that offers a substantially larger core volume and more efficient fin design compared to the factory tube-and-fin unit. Lower intake air temperatures translate directly into denser air charge, allowing the ECU to run more aggressive ignition timing and deliver consistent power even during sustained hard driving. This guide walks you through every step of the installation process, from gathering tools to the first test drive, so you can confidently complete the upgrade in your garage.

Understanding the TurboXS Intercooler Advantage

Before diving into the wrench work, it helps to understand exactly what makes the TurboXS intercooler an effective upgrade. The kit is engineered specifically for the Subaru Forester (and related platforms like the WRX and STI), so it mounts directly to the factory locations without requiring custom brackets or cutting.

Bar-and-Plate vs. Tube-and-Fin Design

The stock intercooler uses a tube-and-fin construction. While lightweight and cost-effective, tube-and-fin cores are less efficient at shedding heat and are more prone to heat soak during stop-and-go driving. The TurboXS intercooler uses a bar-and-plate core, which features internal turbulators that increase the surface area available for heat transfer. This design also holds up better under higher boost pressures without deforming.

Larger Core Volume and Flow Capacity

The TurboXS unit features a thicker core and more internal flow passages than the OEM intercooler. More volume means the air has more time to shed heat as it travels through the core. Additionally, the inlet and outlet diameters are optimized to match the 2.5-inch (or larger) charge piping commonly used in stage 2 and stage 3 setups. This reduces restriction and helps the turbo spool more freely.

Built-In Bypass Valve Provisions

Many Forester owners who upgrade their intercooler also switch to an aftermarket blow-off valve or bypass valve. The TurboXS kit includes the necessary mounting provisions and a flange compatible with common bypass valves, simplifying what would otherwise require fabrication or an adapter plate.

Tools and Materials Needed

Having everything on hand before you start saves trips to the parts store and keeps the job moving. The TurboXS intercooler kit includes the intercooler core, mounting brackets, silicone hoses, and clamps. You will need to supply the following tools and consumables:

  • Socket set — 1/4-inch and 3/8-inch drive with 8 mm, 10 mm, 12 mm, and 14 mm sockets
  • Combination wrenches — 10 mm, 12 mm, 14 mm
  • Screwdrivers — flathead (for prying hose clamps) and Phillips (for plastic fasteners)
  • Torque wrench — capable of reading in the 10–40 ft-lb range
  • Hose clamp pliers (or locking pliers) for spring-style clamps
  • Shop towels or rags — expect some oil residue in the charge pipes
  • Safety glasses and work gloves
  • Permatex silicone gasket maker (or similar high-temp RTV) — for resealing the bypass valve flange if you reuse the stock unit
  • Penetrating oil (e.g., WD-40 or PB Blaster) — for stubborn bolts

Optional but recommended: a Grimmspeed or TurboXS bypass valve if you plan to replace the stock bypass valve while you have everything apart.

Preparation and Safety

A successful install is built on a safe, organized workspace. Take the following steps before turning a single bolt:

  • Park on level ground and engage the parking brake. Chock the rear wheels for added security.
  • Disconnect the negative battery terminal using a 10 mm wrench. Isolate the cable end so it cannot accidentally contact the post.
  • Allow the engine to cool completely. The intercooler sits directly above the turbocharger and exhaust manifold; working on a hot engine risks burns and makes rubber hoses harder to remove.
  • Remove the engine undercover (if equipped) to access the lower intercooler mounting bolts and provide better airflow while you work.

If your Forester has an aftermarket intake system that relocates the air filter, note any potential clearance issues. The TurboXS intercooler is designed to work with most aftermarket intakes, but you may need to adjust intake tube positioning slightly.

Removing the Stock Intercooler

The stock intercooler is held in place by four 12 mm bolts (two on each side) and connected to the intake system via rubber couplers. Follow this sequence carefully to avoid damaging plastic fittings or hoses:

Step 1: Disconnect the Air Intake Duct

Loosen the clamp at the turbo compressor inlet and the clamp at the air filter housing. Remove the intake duct and set it aside. This clears workspace directly above the intercooler.

Step 2: Remove the Intercooler-to-Throttle Body Hose

The large rubber hose connecting the intercooler outlet to the throttle body (sometimes called the “Y-pipe”) is secured with two clamps. Loosen both clamps and work the hose off each fitting. If the hose is stuck, use a flathead screwdriver to gently pry the edge while rocking the hose side to side.

Step 3: Disconnect the Turbo-to-Intercooler Hose

At the bottom of the intercooler on the driver’s side, you’ll find the hose that connects to the turbocharger compressor outlet. Loosen the clamp and pull the hose free. Expect a small amount of oil residue—this is normal blow-by from the PCV system.

Step 4: Disconnect the Bypass Valve Hose

The bypass valve (often called a blow-off valve) is mounted on the top of the intercooler. Disconnect the small vacuum line that runs from the intake manifold to the bypass valve. Also loosen the clamp securing the bypass valve to the intercooler flange if you plan to reuse it.

Step 5: Unbolt the Intercooler

Using a 12 mm socket, remove the four bolts that secure the intercooler brackets to the engine bay. Two bolts are located near the front of the intercooler, and two are near the firewall. With all four bolts removed, lift the intercooler straight up and out. You may need to tilt it slightly toward the passenger side to clear the turbo housing.

Comparing the Stock and TurboXS Intercooler

Take a moment to compare the two units side by side before installing the new one. The differences in core thickness, fin density, and overall weight are immediately visible. The stock intercooler uses thin aluminum fins that can bend easily, while the TurboXS bar-and-plate construction feels significantly more rigid. This is a good time to measure and confirm that the new intercooler’s inlet and outlet positions match the factory piping. If there is a discrepancy, the silicone hoses included in the kit will accommodate minor differences in angle and length.

Installing the TurboXS Upgraded Intercooler

Installation is largely the reverse of removal, but attention to detail is critical for a leak-free fit.

Step 1: Transfer the Bypass Valve

If you are reusing the stock bypass valve, remove it from the old intercooler by loosening the two Phillips-head screws or hex bolts. Clean the mounting surface on the new TurboXS intercooler with a degreaser. Apply a thin bead of high-temp RTV silicone to the gasket surface, then mount the bypass valve. Tighten the screws evenly to avoid warping the plastic valve body.

Step 2: Install the TurboXS Intercooler

Lower the TurboXS intercooler into the engine bay, ensuring it does not pinch any wiring harnesses or vacuum lines. The mounting tabs on the intercooler should line up directly with the factory mounting holes. If they do not align perfectly, loosen the four bracket bolts on the intercooler (the brackets have slight adjustability) and shift the intercooler as needed.

Step 3: Secure with Hardware

Insert the provided bolts (or reuse the stock bolts if they are in good condition) and hand-tighten them first. Once all four bolts are started, use a torque wrench set to 18 ft-lb to tighten them in a crisscross pattern. Over-tightening can crack the intercooler end tanks or strip the threads in the mounting brackets.

Step 4: Connect the Turbo Outlet Hose

Slide the turbo-to-intercooler hose onto the turbo compressor outlet and the intercooler inlet. Use the supplied silicone coupler if the original hose does not fit snugly. Secure both ends with constant-tension hose clamps (included in the kit). Tighten until the clamp is just snug—do not overtighten or you may cut into the silicone hose.

Step 5: Connect the Throttle Body Hose

Install the hose connecting the intercooler outlet to the throttle body. Again, use the silicone coupler provided with the kit if needed. Ensure the hose fully seats on each fitting before tightening the clamps.

Step 6: Reconnect the Bypass Valve Vacuum Line

Reattach the small vacuum hose to the barb on the bypass valve. If the hose is cracked or brittle, replace it with 3/16-inch vacuum line, available at any auto parts store.

Step 7: Reinstall the Intake Duct

Reconnect the air intake duct from the air filter housing to the turbo inlet. Tighten both clamps securely. Double-check that the intake duct is not contacting any moving parts or rubbing against sharp edges.

Post-Installation Inspection and Leak Check

A boost leak can undermine the performance gains from your new intercooler. Take these steps before starting the engine:

  • Visual inspection — Confirm all hose connections are fully seated and clamps are tight. Look for any pinched vacuum lines or wiring.
  • Reconnect the battery and tighten the terminal clamp securely.
  • Prime the fuel system — Turn the ignition key to the ON position for two seconds (do not crank), then turn it OFF. Repeat this cycle three times to prime the fuel pump.
  • Start the engine and let it idle for 2–3 minutes. Listen for any hissing sounds from the intercooler connections. If you hear a leak, shut off the engine and recheck the hose clamps.
  • Check for codes — If the check engine light illuminates, use a code reader to pull the diagnostic trouble code. A P0171 (system too lean) or P0244 (wastegate solenoid) code may indicate a boost leak or vacuum leak.

For the most thorough verification, you can build a simple boost leak tester from a PVC cap and a Schrader valve. Attach the tester to the turbo inlet, pressurize the system to 15–20 psi using a shop air compressor, and listen/look for leaks. Soapy water sprayed on each joint will bubble at leak points. This test is especially valuable if you are running an aftermarket engine tune that targets higher boost levels.

Test Drive and Performance Verification

Once the engine is running smoothly and no leaks are detected, take the Forester for a controlled test drive. Follow this procedure to confirm the installation is successful:

  • Drive gently for the first 5 minutes to allow the intercooler to stabilize thermally.
  • Make several part-throttle pulls from 2,500 to 5,000 RPM in third gear. Notice how the engine responds to throttle inputs; the TurboXS intercooler should deliver sharper throttle response due to reduced pressure drop.
  • Monitor intake air temperatures (IATs) using an OBD-II scanner or a device like the UltraGauge. Compare the IAT reading after a sustained pull to what you observed with the stock intercooler. You should see lower peak IATs, and the temps should drop back toward ambient more quickly once you lift off the throttle.
  • Listen for unusual noises — a whistling or chirping sound under boost may indicate a small leak or a loose clamp. A metallic rattling can indicate the intercooler is contacting a chassis component; if you hear this, check clearance at the mounting brackets.

Tuning Considerations

While the TurboXS upgraded intercooler provides a meaningful performance gain as a bolt-on part, its full potential is unlocked when combined with an appropriate engine management tune. The denser, cooler air entering the engine will change the air/fuel ratio and may cause the ECU to pull timing if the calibration is not optimized.

  • Stage 2 or Stage 3 tunes — Most off-the-shelf (OTS) tunes from companies like Cobb Tuning or AccessECU assume a larger intercooler and include fuel and spark maps tailored for cooler intake air.
  • Custom dyno tuning — For maximum power and reliability, a custom tune from a Subaru specialist is ideal. The tuner can optimize timing advance and fuel enrichment based on your specific driving conditions and fuel octane.
  • Ethanol blends — If you plan to run E30 or E85, the upgraded intercooler is even more beneficial because ethanol-powered engines produce more heat and require higher fueling capacity.

Maintenance Tips for Long-Term Performance

An intercooler is a passive component, but it does require periodic inspection to maintain its efficiency.

  • Check for debris — The front of the intercooler core can accumulate bugs, road debris, and small rocks. Clean the fins gently with compressed air or a low-pressure water spray. Do not use a pressure washer directly on the fins, as this can bend them and restrict airflow.
  • Inspect hoses and clamps — Silicone hoses can harden and crack over time, especially near the turbo outlet where temperatures are highest. Replace any hose that feels brittle or shows signs of oil seepage.
  • Recheck clamp torque — After the first 500 miles, re-tighten all hose clamps. Thermal cycling can cause clamps to loosen slightly.
  • Look for oil accumulation — Some oil residue in the intercooler is normal due to the PCV system. However, if you find puddles of oil at the bottom of the intercooler, your turbocharger’s seal may be failing. Address this promptly to prevent oil from entering the intake system.

Frequently Asked Questions

Will the TurboXS intercooler fit my Forester XT?

Yes, the TurboXS upgraded intercooler is designed for the Subaru Forester XT (2004–2018) as well as the WRX and STI models with the same engine bay layout. Always verify your model year and engine code (EJ255, EJ257, or FA20) before ordering.

Do I need to upgrade my intercooler if I only have a cat-back exhaust?

At stage 1 (cat-back exhaust only), the stock intercooler is adequate. The upgraded intercooler becomes a worthwhile upgrade at stage 2 (downpipe, tune) or if you drive in hot climates where heat soak is a constant issue.

Can I install the intercooler without a tune?

Yes, you can physically install the intercooler without reflashing the ECU. The engine will run, but you will not realize the full performance benefit. The ECU may also learn around the improved airflow by trimming fuel trims negatively, leading to a leaner-than-ideal mixture. A tune is strongly recommended to maximize safety and power.

How long does the installation take?

A first-time installer working in a home garage should budget 2.5 to 4 hours. Experienced Subaru enthusiasts can complete the swap in about 1.5 hours.

Conclusion

Swapping the stock intercooler for the TurboXS upgraded intercooler is one of the most effective bolt-on modifications you can perform on a Subaru Forester. It directly addresses the heat soak and pressure loss limitations of the factory unit, resulting in cooler intake air, more consistent power, and reduced knock risk under hard driving. By following this step-by-step guide—and paying careful attention to hose routing, torque specifications, and post-installation leak testing—you can complete the upgrade confidently in your own garage.

The investment in a quality intercooler pays dividends every time you press the throttle, whether you are daily driving in summer traffic or exploring the Forester’s performance potential on a winding back road. Pair your new intercooler with a professionally calibrated tune, and you will unlock a noticeably sharper, stronger driving experience that makes the Forester feel like a completely different vehicle.