Parts for your 1998 Daihatsu Gran move-Thermostat

1998 Daihatsu Gran Move Thermostat — what it does and how to keep it happy

Yes, the 1998 Daihatsu Gran Move uses a thermostat. This is confirmed by the Daihatsu Pyzar/Gran Move (G3 series) workshop manual’s Cooling System section, which details a wax‑type thermostat mounted in the water outlet housing on the cylinder head for the HC‑EJ 1.5‑litre engine. The Daihatsu Electronic Parts Catalogue for Gran Move/Pyzar models also lists a thermostat assembly and matching seal for the same engine, and major AU/NZ application guides (e.g., Tridon/Gates) catalogue direct replacement thermostats for the 1997–2000 Gran Move 1.5. Together, these technical sources make it clear the thermostat is standard equipment on this vehicle.

For this Gran Move, the thermostat is the quiet hero that gets the engine up to its proper operating temperature quickly, then keeps it there. By controlling coolant flow between the engine and radiator, it helps the 1.5‑litre HC‑EJ run efficiently, keeps fuel use sensible, protects against excess wear, and makes sure the cabin heater actually blows warm on a frosty morning in Aotearoa or a chilly Melbourne start.

When servicing, it’s smart to think of the thermostat as a low‑cost insurance item. If the car has overheated, if the coolant’s been neglected, or if the part is original after decades, replacement is prudent. Stick with an OE‑equivalent temperature rating (typically in the low‑80s °C range as specified in the service literature) rather than a “colder” race unit, which can cause over‑cooling and higher fuel consumption in everyday driving.

Common red flags include slow warm‑up and a heater that never really gets toasty (stuck open), or sudden temperature spikes and a hard top hose that stays cold then surges hot (stuck closed). Poor idle quality, higher fuel use, and a sweet coolant smell after short runs can also hint at trouble.

Replacement is straightforward for a competent DIYer: start with a stone‑cold engine, drain a little coolant, remove the water outlet housing (usually a couple of small bolts), note the thermostat’s orientation (jiggle‑pin notch up if fitted), clean the mating surfaces, fit a new thermostat with the correct O‑ring or gasket, and reassemble. Don’t over‑torque the small housing bolts. Refill with the correct coolant mix (de‑mineralised water and quality concentrate per the service manual), bleed air by running the engine with the heater on hot and the nose slightly uphill, squeeze the upper hose to burp bubbles, then recheck the level after a short drive. If there’s any doubt about age or condition, pairing thermostat renewal with a fresh radiator cap and an on‑time coolant change keeps the Gran Move’s cooling system tidy and dependable.

• Tip: Any time the cooling system is opened, plan on a new housing seal and a fresh coolant top‑up.

Popular questions

Where is the thermostat on a 1998 Daihatsu Gran Move?
It sits in the water outlet housing at the cylinder head end of the upper radiator hose. Follow the top hose back to the engine, the housing it bolts to contains the thermostat and its seal. Access is usually from above with basic hand tools.

What temperature thermostat should be used?
Use an OE‑spec unit in the low‑80s °C opening range as specified in Daihatsu’s service documentation for the HC‑EJ engine. That balance gives quick warm‑up, stable running, and proper heater performance for everyday AU/NZ conditions.

Do you need to bleed the cooling system after changing the thermostat?
Yes. Park nose‑up, set the heater to hot, fill the radiator and overflow bottle, run the engine to operating temp, and gently squeeze the top hose to purge air. Top up as bubbles clear, let it cool, and recheck the level. Some cars may need a couple of heat cycles to settle.