Parts for your 2009 Honda Stream-Thermostat

2009 Honda Stream Thermostat — Purpose and Service Advice

Based on Honda workshop literature for the Stream RN6–RN9 series (2007–2014) and Honda’s electronic parts catalogues listing a “Thermostat Assembly” for the R18A and R20A engines, the 2009 Honda Stream is fitted with a conventional, wax‑pellet engine coolant thermostat. Honda service data for the R‑series engines specifies a thermostat that begins to open around 80–84°C and is fully open near 95°C, housed at the engine end of the lower radiator hose. So yes—this vehicle absolutely uses a thermostat.

The thermostat’s job is to help the Stream warm up quickly and then hold a steady operating temperature. By controlling coolant flow between the engine and radiator, it keeps the engine in the sweet spot for power, economy, emissions, and heater performance. Too cold and fuel economy suffers, too hot and there’s a risk of overheating and long‑term damage.

As a service item, the thermostat isn’t replaced on a strict schedule, but age, kilometres, or poor coolant quality can make it sluggish or stuck. Many technicians in Australia and New Zealand treat it as prudent maintenance at major cooling‑system work (for example, after a water pump or radiator replacement), or around the 8–10 year/160,000–200,000 km mark if there are tell‑tale signs.

• Common symptoms: slow warm‑up, heaters staying cool, erratic gauge behaviour, overheating, or DTC P0128 (coolant temperature below regulating threshold).
• Best practice: use a quality OEM‑spec thermostat and new O‑ring, and refill with Honda Type 2 (blue) long‑life coolant. Don’t mix coolant types.

The thermostat on the 2009 Stream sits in an alloy housing at the block side of the lower radiator hose. Replacement is straightforward: drain enough coolant to drop the level, remove the housing, swap the thermostat and O‑ring, and torque the housing bolts to spec (light—check the manual). The jiggle pin/air bleed on the thermostat should face up. Refill, run the engine with the heater on hot, and bleed air to avoid hot spots.

Owners should also keep an eye on hoses, clamps, and the radiator cap, as weak caps can mimic thermostat faults. If the Stream consistently runs cool on the open road or overheats in traffic, a thermostat check is cheap insurance before chasing more complex issues.

Popular questions about the 2009 Honda Stream thermostat

Where is the thermostat located on a 2009 Honda Stream?
It’s mounted in the thermostat housing at the engine end of the lower radiator hose, typically low on the front of the engine. On R‑series engines, access is from above with the intake ducting out of the way, two housing bolts secure it, and there’s a rubber O‑ring seal.

What are the signs the thermostat needs replacing?
Expect slow cabin warm‑up, temperature gauge sitting low on the motorway, or overheating and coolant boil‑over in traffic. The ECU may log P0128. If the top radiator hose stays cold for too long after start‑up or never warms evenly, the thermostat could be stuck.

What coolant should be used after thermostat replacement?
Honda Type 2 (blue) premixed coolant is the go‑to. Capacity is roughly 5–6 litres depending on engine and how much is drained. Refill slowly, set the heater to hot, and bleed air to prevent hotspots and false temperature readings.