Parts for your 2013 Subaru Legacy-Thermostat

2013 Subaru Legacy thermostat — what it does and when to replace it

Based on Subaru’s factory service information and parts catalogues for the 2013 Legacy/Outback (FB25 2.5‑litre and EZ36 3.6‑litre), this model absolutely uses a conventional engine coolant thermostat. Subaru documents describe a wax‑pellet thermostat mounted at the water pump inlet/lower hose area, confirming it’s a relevant and serviceable part on this vehicle.

The thermostat’s job is simple but critical: it helps the engine warm up quickly, then keeps coolant circulating at the right temp for efficient running. Cold start? It stays shut to bring the engine up to operating temperature fast, improving fuel economy, emissions, and cabin heater performance. Once near its set temperature, it opens to let coolant flow through the radiator. That steady temperature protects head gaskets, prevents over‑cooling on the highway, and stops heat‑soak in traffic.

On the 2013 Legacy, the thermostat sits low in the system, so fresh coolant and proper bleeding matter. Most owners won’t have a strict replacement interval in the maintenance schedule, it’s typically a “replace on condition” item. Good times to fit a new one include when doing a major cooling service, after an overheating event, or if symptoms below show up.

• Slow warm‑up or weak cabin heat (can point to stuck‑open)
• Overheating or sudden temp spikes (can point to stuck‑closed)
• Erratic gauge swings, fans running oddly, or coolant pushed into the overflow

When replacing, use a genuine‑spec thermostat and new seal/O‑ring, and install it in the correct orientation (jiggle pin at 12 o’clock if fitted). Drain coolant to below the housing, clean the mating surfaces, and refit evenly without overtightening. Refill with Subaru‑approved blue long‑life coolant (pre‑mix) or the correct spec for local supply, and bleed air with the heater on full hot. A spill‑free funnel helps avoid air pockets, top up the overflow bottle to the mark and recheck levels over the next few short drives.

A healthy cooling system is a package deal: the thermostat, radiator cap, fans, hoses, and the coolant itself. Keeping that lot tidy and leak‑free will help the Legacy’s flat‑four or flat‑six run sweet for many kilometres.

Popular questions

What temperature does the thermostat open on a 2013 Subaru Legacy?
Subaru service data indicates the thermostat begins to open in the high‑70s to low‑80s °C range and is fully open roughly in the low‑90s °C. Exact figures vary slightly by engine (FB25 vs EZ36) and supplier, but that’s the normal window for proper warm‑up and cooling control.

How often should the thermostat be replaced?
There’s no fixed kilometre interval in most schedules. Replace it if there are symptoms, evidence of overheating, corrosion, or when doing major cooling work. Many owners choose preventative replacement around the 10‑year/150–200,000 km mark, using an OEM thermostat and fresh seal.

Is it safe to drive with a faulty thermostat?
Not really. Stuck‑open can cause over‑cooling, poor heater output, higher fuel use, and potential long‑term wear. Stuck‑closed can lead to rapid overheating and engine damage. If the gauge misbehaves or it overheats, stop, let it cool, and sort the fault before driving on.