Parts for your 2013 Subaru Outback-Thermostat

2013 Subaru Outback Thermostat — purpose, placement, and service tips

Based on technical sources including the Subaru Factory Service Manual for MY2013 Outback/Legacy (Cooling System section) and Subaru’s parts catalogue for the FB25 2.5‑litre and EZ36 3.6‑litre engines, this model absolutely uses an engine coolant thermostat. It’s a wax‑pellet type unit mounted at the water pump inlet on the lower radiator hose side. So yes — a thermostat is relevant, fitted, and critical on the 2013 Subaru Outback.

The thermostat’s job is to help the Outback reach and hold its ideal operating temperature, typically in the low 90s °C. When the engine is cold it stays shut, speeding warm‑up, improving fuel economy, and giving the cabin heater a head start. As temperature rises, it progressively opens, letting coolant flow through the radiator to keep things stable. Without a healthy thermostat the Outback can run too cool (sluggish warm‑up, higher fuel use, poor heater performance) or too hot (overheating risk), and may even throw a P0128 fault if it never gets warm enough.

There’s no strict time‑based replacement interval in the Subaru schedule, these are usually replaced on condition. That said, many techs treat the thermostat as a preventative item at higher kilometres, or any time the cooling system is apart for a water pump, radiator, or timing service (where applicable). If the temperature gauge wavers, the heater fluctuates, fans cycle oddly, or there’s coolant loss with no obvious leak, the thermostat is a usual suspect.

For a 2013 Outback, quality OEM‑spec parts and a fresh gasket/O‑ring are a must. The unit lives low on the engine behind the lower radiator hose, so expect some coolant loss. Under the bonnet, allow the engine to cool completely, drain enough coolant for clean access, swap the thermostat in the correct orientation, and torque the housing evenly. Refill with the correct Subaru‑approved coolant mix and bleed air carefully — run the engine with the heater on hot, top up as bubbles purge, and recheck the level after a short drive. Using the right coolant, keeping the system clean, and replacing ageing hoses and caps will help the new thermostat last the distance.

• Watch for P0128, slow warm‑up, uneven cabin heat, or creeping temps.
• Use OEM‑quality thermostat and new seal, don’t reuse crusty gaskets.
• Bleed the system thoroughly and recheck levels over the next few drives.

Popular questions

Where is the thermostat on a 2013 Subaru Outback?

It’s mounted in the thermostat housing at the water pump inlet, where the lower radiator hose connects to the engine. On both the FB25 and EZ36, access is from below the front of the vehicle. Drain some coolant first to avoid a mess and fit a new gasket or O‑ring on reassembly.

What are the common signs the thermostat needs replacing?

Slow warm‑up, poor heater output, a P0128 code, temp gauge that drifts up and down, or overheating under load are all red flags. If hoses stay cold long after start‑up or the top hose gets rock‑hard quickly, the thermostat may be stuck closed or not opening correctly.

Should the thermostat be replaced with OEM or is aftermarket fine?

High‑quality OEM or proven OEM‑equivalent thermostats are recommended. The correct temperature rating, proper opening profile, and a reliable seal matter on these engines. Cheap units can cause erratic temperatures or early failure, so it’s worth fitting a reputable brand and the correct Subaru‑spec gasket.