Subaru Forester: EJ Coolant System Degradation (Hoses, Thermostat, Radiator)

SF and SG Forester cooling systems suffer from a combination of age-related rubber hose deterioration, plastic radiator tank cracking at the crimped seam, and thermostat housing corrosion. The EJ engine runs a closed-deck aluminium block that is sensitive to coolant pH degradation — Subaru Super Coolant (blue) must be used and replaced every 30,000 km or the silicate inhibitors deplete, causing aluminium corrosion and silting that blocks the heater core and radiator passages. Radiator fan thermal switch failure also causes overheating in stationary traffic.

• Coolant leak from lower or upper radiator hose couplings
• Overheating in slow traffic but normal temperature at highway speed
• Heater output weak or intermittent (blocked heater core)
• Coolant reservoir shows rust-coloured or brown discolouration

1. 1

   Inspect all radiator hoses when cold for cracks, swelling near clamps, or oil contamination.

2. 2

   Squeeze hoses — they should feel firm, not spongy or brittle.

3. 3

   Check coolant colour in the reservoir: should be clean blue/green, not brown or rust-tinged.

4. 4

   Inspect the plastic top tank of the radiator along the crimp line for hairline cracks or seepage staining.

5. 5

   With engine at operating temperature, confirm both radiator fans cut in.

6. 6

   Check thermostat housing for weeping at the gasket.

Parts involved: Thermostat, Radiator.

$300 to $1,800 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.

• “When was the coolant last flushed and replaced, and which coolant type was used?”
• “Has the vehicle ever overheated or shown temperature gauge abnormalities?”
• “Has the radiator or any hoses been replaced?”

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.