Parts for your 2017 Holden Colorado-Thermostat housing

2017 Holden Colorado thermostat housing — what it does and how to look after it

Based on the Holden RG Colorado Workshop Manual (MY16–MY20, Cooling System section), GM Global Service Information for the 2.8 Duramax diesel (RPO LWN/XLD28), and Holden/ACDelco parts catalogues that list a complete thermostat-and-housing/coolant outlet assembly for MY17 RG Colorado, this vehicle does use a thermostat housing. It’s a dedicated alloy/composite outlet bolted to the engine that contains the thermostat and provisions for the coolant temperature sensor and hose connections.

On the 2017 Holden Colorado, the thermostat housing is the gateway that controls when hot coolant leaves the engine for the radiator. By holding coolant back until the diesel reaches operating temperature, it helps the ute warm up quickly, run efficiently, and keep cabin heat reliable. Once up to temp, the housing and thermostat work together to stabilise temps under load — which matters whether it’s towing, off-roading, or slogging through summer traffic. The housing also provides a tidy place for the coolant temp sensor and a leak-free junction for the upper radiator hose.

It’s not a scheduled replacement item, but it does deserve attention during routine servicing. A quick look for pink/orange crust from dried coolant, dampness around the gasket or hose neck, or hairline cracks in the body can save a drama later. If the vehicle throws a P0128 code, warms up too slowly, runs hot on climbs, or the heater goes cold at idle, the thermostat assembly is a usual suspect.

When replacement is due, most RG Colorados are best served by swapping the complete thermostat-and-housing assembly rather than just the thermostat. Use an OE or OE-quality unit with a new O-ring/gasket. Work on a cold engine, safely drain enough coolant, disconnect the temp sensor, remove the upper hose and housing bolts, clean the mating face, then refit and torque per the workshop manual. Refill with Holden/ACDelco Dex‑Cool–approved OAT coolant (pre-mix or 50/50 with demineralised water), bleed air out, and confirm the heater runs hot and fans cycle normally. After a short road test, recheck for leaks and top the reservoir to the MAX mark once it cools.

• Service tip: Inspect the housing, hose neck and clamps at every service, replace brittle hoses at the same time.
• Towing or heavy off‑road use: check more frequently, as heat cycles are harsher.
• After any overheat: test or replace the thermostat assembly to avoid repeat issues.

Where is the thermostat housing on a 2017 Holden Colorado?

It’s at the front of the engine where the upper radiator hose meets the engine. That assembly is the coolant outlet/thermostat housing and usually also carries the coolant temperature sensor.

What coolant should be used after replacing the housing?

Use a Dex‑Cool–approved OAT long‑life coolant specified by Holden/ACDelco. Choose the correct colour/type for RG Colorado and run either a premix or a 50/50 mix with demineralised water. Avoid mixing coolant types to keep corrosion protection and seal life on point.

Can the thermostat be replaced without changing the housing?

On many 2017 RG Colorados the thermostat is supplied integrated with the housing and seal, so it’s typically replaced as a complete assembly. That approach reduces leak risks and saves time.