CriticalCommonCooling

Subaru STI: EJ20/EJ205 Water Pump Plastic Impeller Failure (GC/GF and GD/GG)

EJ20/EJ205 Water Pump Plastic Impeller Failure (GC/GF and GD/GG) is a common cooling fault on the Subaru STI on the 1994–2007 cars, and we rate it critical. Putting it right costs $450 to $950 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 32 documented faults on the Subaru STI.

Vehicle: Subaru STI
Engine: EJ20 / EJ205
Years: 1994–2007
Fuel: petrol
System: Cooling

This page covers the Subaru STI as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Subaru STI faults32 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the Water pump yet. We would rather show none than show a picture of a different part.

What goes wrong

Subaru's factory water pump on EJ-series engines uses a plastic impeller that degrades and spins free on its shaft over time, dramatically reducing coolant flow without triggering any visible external leak. The failure is insidious — the pump still turns and appears normal externally, but coolant is barely circulating, leading to gradual or sudden overheating. An overheating event in an EJ Subaru with a failed impeller frequently precedes head gasket failure. The pattern is documented across GC/GF and GD/GG WRX and STI models spanning 1994 to 2007. Replacement with an aftermarket metal-impeller unit is the accepted long-term fix.

What you would notice

Gradual or intermittent engine overheating with no visible coolant leak
Temperature gauge creeping high under sustained load
Coolant level dropping with no visible external leak
Overheating events that cool once stationary (fan working but coolant not circulating)

How to check it

Where to look. Water pump on the front of the EJ engine block, driven by the cambelt

Monitor the coolant temperature gauge closely during a sustained test drive under load, including hills.
Check the coolant reservoir level and condition.
Ask specifically about any overheating history — a past overheat is a major red flag for downstream head gasket damage on these engines.

Parts involved: Water pump.

What it costs to put right

$450 to $950 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has the water pump been replaced? If so, was it replaced with a metal-impeller unit?”
“When was the cambelt last replaced — was the water pump changed at the same time?”
“Has the car ever overheated?”

Now check the Subaru STI you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.

Subaru STI buyer questions

Is ej20/ej205 water pump plastic impeller failure (gc/gf and gd/gg) serious on a Subaru STI?

We rate it critical and common on the Subaru STI. Subaru's factory water pump on EJ-series engines uses a plastic impeller that degrades and spins free on its shaft over time, dramatically reducing coolant flow without triggering any visible external leak. The failure is insidious — the pump still turns and appears normal externally, but coolant is barely circulating, leading to gradual or sudden overheating. An overheating event in an EJ Subaru with a failed impeller frequently precedes head gasket failure. The pattern is documented across GC/GF and GD/GG WRX and STI models spanning 1994 to 2007. Replacement with an aftermarket metal-impeller unit is the accepted long-term fix.

How much does it cost to fix on a Subaru STI?

$450 to $950 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Subaru STI years are affected?

Our research records this fault on the 1994–2007 Subaru STI. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.

How do I check for it before I buy?

Monitor the coolant temperature gauge closely during a sustained test drive under load, including hills. Check the coolant reservoir level and condition. Ask specifically about any overheating history — a past overheat is a major red flag for downstream head gasket damage on these engines. Look here: Water pump on the front of the EJ engine block, driven by the cambelt