Parts for your 2000 Holden Commodore-Thermostat

2000 Holden Commodore Thermostat — Purpose, fitment and service tips

Yes, the 2000 Holden Commodore uses a thermostat. This applies to the VT Series II and early VX models with the 3.8L ECOTEC V6 and the 5.7L Gen III V8. Fitment and operation are documented in the Holden VT/VX Service Manual (Engine — Cooling System, 6 Cyl & 8 Cyl) and GM Powertrain service information for the 3800 Series II and LS1 engines, as well as ACDelco parts catalogues listing thermostats for these models.

The thermostat’s job is to regulate coolant flow so the engine reaches and maintains its ideal operating temperature. Closed when cold, it lets the engine warm up quickly for smoother running, better fuel economy, lower emissions and decent cabin heat. As temperature rises, it opens to let coolant circulate through the radiator. Factory-spec units typically begin opening around the 90°C mark. Running the correct-rated thermostat keeps the temp gauge steady and the fans behaving as they should.

Location-wise, V6 owners will find the thermostat under the alloy outlet/neck at the front of the intake area, beneath the bonnet line. On the LS1 V8, it’s integrated near the water pump housing. Either way, it’s a straightforward remove-and-replace job for a competent home mechanic with basic tools and a catch pan.

When replacing, go for a quality thermostat and always fit a fresh O‑ring or gasket. Drain enough coolant to sit below the housing, crack the housing bolts evenly, and clean the mating surfaces. Refill with the correct long‑life OAT coolant (red) mixed with demineralised water as per Holden guidance, then bleed out air so there are no hot spots or fluctuating temps. After a short road test, recheck the level and look for weeps around the housing.

• Common faults: stuck open (cold running, weak heater, high fuel use) or stuck closed (overheating, hard hoses, boiling).
• Service tip: thermostats aren’t a time-based replacement, but they’re smart to do during major cooling system work or if there are temperature irregularities.
• Good practice: inspect hoses, radiator cap, fans and water pump at the same time, temperature issues are often a system story, not just one part.

Regularly changing coolant at recommended intervals helps keep the thermostat and passages clean, reducing corrosion and sticky operation over time.

Popular questions

Where is the thermostat on a 2000 Holden Commodore?
On the 3.8L V6, it sits under the alloy thermostat outlet at the front of the engine near the intake area. On the 5.7L LS1 V8, it’s mounted at the water pump/thermostat housing assembly. Either location is easy to reach from the top once the engine cover is off.

Look for the outlet where the top radiator hose connects to the engine — that’s the giveaway on both engines.

What temperature thermostat should be used?
Most stock replacements for the 2000 Commodore are around 90°C opening temperature, matching factory intent. That keeps warm‑up quick and the gauge steady under Aussie and Kiwi conditions.

Lower-temp options exist, but for a road car it’s best to stick with the OE-rated spec to maintain proper fuel trims, emissions and heater performance.

How can someone tell if the thermostat is failing?
If it’s stuck open, the gauge lingers low, fuel use climbs and the cabin heater feels weak. If it’s stuck closed, the engine overheats, the upper hose goes rock hard and coolant may boil.

Before blaming the thermostat, check coolant level, radiator cap condition and fan operation, as these can mimic similar symptoms.