Parts for your 2011 Honda Stream-Thermostat housing

2011 Honda Stream thermostat housing — what it does and when to service it

Based on Honda’s Electronic Parts Catalogue for the RN6–RN9 Stream (2011 model year) and the Honda workshop manual procedures for R18A/R20A cooling systems, the 2011 Honda Stream is fitted with a thermostat housed in the water outlet (commonly called the thermostat housing). These technical references show the thermostat, housing/water outlet, O-ring/gasket, and related sensors as standard components.

The thermostat housing on a 2011 Honda Stream keeps coolant flow in check and the engine running at the sweet-spot temperature. It’s the mounting point for the thermostat itself, routes coolant from the cylinder head to the radiator, and often carries a temperature sensor. On many Streams it’s a durable composite/plastic body, over time heat cycles and minerals in old coolant can cause the O-ring to harden, or the housing to warp or crack, leading to pesky leaks.

For day-to-day ownership, there’s no fixed replacement interval for the housing, but it should be inspected whenever the cooling system is serviced. Good practice for Aussie and Kiwi drivers is to refresh coolant with Honda Type 2–equivalent premix at the recommended interval and check the housing for seepage, white crusty residue, or staining around the joint. If the engine runs cool for ages, overheats, or the heater goes cold at idle, the thermostat or housing may be at fault.

When replacement is needed, it’s a straightforward job for a competent DIYer or mechanic:

• Let the engine cool fully, then drain enough coolant to sit below the housing level.
• Remove the upper hose and any sensors or wiring on the housing.
• Unbolt the housing, lift out the thermostat, and clean the mating surface.
• Fit a new thermostat and O-ring/gasket, refit the housing, and torque fasteners to spec from the Honda manual.
• Refill with the correct coolant, bleed air with the heater on hot, and check for leaks.

It’s smart to replace the thermostat and O-ring whenever the housing is off. If the housing shows hairline cracks, warping, or pitting, swap it for a quality OEM or reputable aftermarket unit. After any cooling system work, a quick pressure test and a couple of short drives will confirm all’s well under the bonnet.

While they’re there, a technician will often check hose condition, clamps, and the radiator cap — cheap parts that can save a long walk if they fail.

Popular questions about 2011 Honda Stream thermostat housing

Where is the thermostat housing on a 2011 Honda Stream?
It’s mounted on the cylinder head, on the transmission side of the engine bay, where the upper radiator hose connects. The thermostat sits inside this water outlet, sealed by an O-ring.

This placement makes it easy to access once the intake ducting is moved aside. Always start with a cool engine to avoid burns.

What are common signs the thermostat housing or thermostat needs replacement?
Coolant weeping or white residue around the housing joint, overheating, slow warm-up, fluctuating temp gauge, or no cabin heat at idle are common flags.

Any visible cracks in the housing or a swollen, flattened O-ring call for replacement. A stuck thermostat is often replaced at the same time.

What coolant should be used after servicing the housing?
Use Honda Type 2 (blue) premixed coolant or an equivalent long-life, silicate-free formula compatible with Honda systems. Don’t mix types, if unsure what’s in there, perform a full drain and refill.

Bleed the system thoroughly and recheck the level after a short drive, topping up the reservoir to the correct mark.