Mishimoto MMHOSE-STI-08BK Silicone Radiator Hose Kit for 2008–2014 WRX and 2008–2021 STI

Important 2015–2021 WRX Warning

This kit does not fit the standard 2015–2021 Subaru WRX with the 2.0L FA20DIT engine.

It fits the WRX STI during those years because the STI retained the EJ257 and compatible cooling-system layout. Subaru’s decision to sell the WRX and STI with completely different engine families under nearly identical names has surely never confused an online parts buyer.

Compatible Models and Trims

Applicable configurations include:

• 2008–2014 Subaru Impreza WRX sedan
• 2008–2014 Subaru Impreza WRX hatchback
• 2008–2014 Subaru Impreza WRX STI sedan
• 2008–2014 Subaru Impreza WRX STI hatchback
• 2015–2021 Subaru WRX STI
• WRX STI Limited
• WRX STI Series special editions with compatible cooling layouts
• 2019 WRX STI S209, subject to direct fitment verification

Verify radiator connections and hose routing on heavily modified or limited-production vehicles.

Reinforced Silicone Construction

The hoses combine high-grade silicone with embedded heat-resistant fibers. Mishimoto rates them for temperatures up to 330°F and improved pressure tolerance over aging factory rubber hoses.

Key features include:

• Reinforced high-grade silicone
• Heat-resistant embedded fibers
• Maximum temperature rating of 330°F
• 1.50-inch inside diameter
• 1.85-inch outside diameter
• Preformed factory-style bends
• Black finish
• Mishimoto Lifetime Warranty

The black finish keeps the engine bay relatively subtle. Not every cooling upgrade needs to announce itself from the opposite end of the parking lot.

What’s Included?

The kit includes:

• One black silicone upper radiator hose
• One black silicone lower radiator hose

Clamp inclusion can vary between retail packages and listings. Confirm whether clamps are supplied before ordering.

This kit does not replace:

• Heater hoses
• Turbocharger coolant hoses
• Coolant crossover hoses
• Expansion-tank hoses
• Oil-cooler coolant hoses
• Every small bypass connection

Factory-Style Fit

The hoses are molded around the factory EJ-series radiator and engine connections. They can also work with many direct-fit aluminum radiators that retain the original inlet and outlet positions.

Verify fitment if the Subaru has:

• An aftermarket or oversized radiator
• A rotated turbocharger installation
• A front-mounted intercooler
• Modified coolant expansion tanks
• A replacement engine with different coolant outlets
• Custom fan or shroud mounting
• Relocated accessories
• Nonstandard water-pump or thermostat components

A thicker radiator can reduce hose clearance near the fans and accessory drive. Check the complete routing before filling the system.

When Should WRX or STI Radiator Hoses Be Replaced?

Replace the hoses if you notice:

• Cracks near the connections
• Soft or swollen sections
• Coolant residue around a clamp
• Oil contamination
• Abrasion against another component
• A hose collapsing during cooldown
• Recurring coolant loss
• Coolant odor after driving
• Temperature fluctuations
• Visible steam or leakage

Use our coolant-leak diagnostic guide if the source is difficult to locate. Inspect the radiator tanks, expansion tank, water pump and thermostat housing—not just the two largest hoses.

Installation Overview

Never remove the radiator or expansion-tank cap while the engine is hot.

A typical installation involves:

1. Confirm the exact WRX or STI model and engine.
2. Photograph the original hose routing.
3. Drain enough coolant to empty both radiator hoses.
4. Remove the factory clamps.
5. Carefully separate the hoses from their connections.
6. Inspect the radiator and engine fittings.
7. Clean each sealing surface.
8. Compare the replacement hoses with the originals.
9. Install both hoses without twisting or stretching them.
10. Position each clamp behind the raised fitting bead.
11. Verify clearance from fans, belts and sharp brackets.
12. Refill with Subaru-compatible coolant.
13. Bleed trapped air from the system.
14. Confirm cooling-fan operation.
15. Inspect each connection at operating temperature.
16. Recheck the coolant level after the engine cools.

Use our cooling-system flush guide if the existing coolant is old, mixed or contaminated.

Bleeding the Subaru Cooling System

Trapped air can interrupt coolant circulation and produce overheating, unstable temperature readings or inconsistent heater output. Fill the system slowly and follow the service procedure for the exact model year.

Stop the engine if:

• The temperature gauge rises rapidly
• The heater suddenly blows cold
• Coolant is forced from the reservoir
• The upper hose remains cold while the engine overheats
• Steam appears
• The radiator fans fail to operate

Our guide to a car overheating while the heater blows cold explains why this combination often points to low coolant or trapped air.

Inspect the Complete Cooling System

New radiator hoses cannot repair a failed thermostat, water pump, radiator or head gasket. Inspect:

• Radiator core and end tanks
• Pressure cap
• Coolant expansion tank
• Water pump
• Thermostat
• Cooling fans and relays
• Heater and bypass hoses
• Turbocharger coolant lines
• Timing-belt service history
• Coolant condition
• Evidence of combustion leakage

Our complete cooling-system guide explains how these parts work together.

Additional diagnostic resources include:

• Why a car overheats while driving
• Seven signs of a failing radiator
• Bad thermostat versus bad water pump
• How to deal with overheating
• Can radiator stop-leak cause damage?
• When should you stop driving?

Frequently Asked Questions

What years does MMHOSE-STI-08BK fit?

It fits the 2008–2014 Subaru WRX and the 2008–2021 Subaru WRX STI.

Does it fit a 2015 Subaru WRX?

No. The standard 2015 WRX uses the FA20DIT engine and a different cooling-system arrangement.

Does it fit a 2015–2021 WRX STI?

Yes. Mishimoto’s current fitment extends through the 2021 STI.

Does it fit both WRX and STI hatchbacks?

It fits compatible 2008–2014 WRX and STI hatchback applications.

Does it fit the EJ255?

Yes, in listed 2008–2014 WRX applications.

Does it fit the EJ257?

Yes, in listed 2008–2021 STI applications.

Are upper and lower hoses included?

Yes. The package contains both primary radiator hoses.

Are clamps included?

Some retail listings show clamps while others specify only two hoses. Confirm the current package contents before ordering.

Will the hoses work with an aluminum radiator?

They should fit a direct-replacement radiator retaining factory inlet and outlet positions. Verify oversized and custom radiators before ordering.

Will silicone hoses lower coolant temperature?

Not directly. They improve hose durability and pressure tolerance. Actual operating temperature depends on coolant circulation, radiator efficiency, thermostat control and airflow.

Product Specifications