Honda Acty — Cooling System

Specifications

Coolant Flush Procedure

The engine and cooling system are located under the truck bed. The bed access panel must be removed to reach the upper and lower radiator hoses, thermostat housing, and water pump. The radiator itself is accessible from under the truck.

1. Ensure the engine is completely cold. Remove the radiator cap and locate the drain plug at the bottom of the radiator on the passenger side. Place a drain pan with sufficient capacity (at least 6 quarts) under the drain.
2. Open the drain plug and allow the coolant to drain fully. Remove the lower radiator hose for better drainage if desired.
3. Close the drain plug and refill the system with plain distilled water. Run the engine briefly to circulate the water through the system, then drain again. Repeat if the flushed water is very dark or rusty.
4. Close the drain plug. Pour in the correct amount of 50:50 premixed coolant — approximately 5.0 liters. Use Honda HP-C (Honda Blue) or any HOAT-compatible coolant. Do not mix green conventional coolant with orange or blue extended-life coolants.
5. Leave the radiator cap off. Start the engine and let it warm up to operating temperature. Watch the coolant level in the radiator neck — as the thermostat opens and coolant circulates, the level will drop. Top up as needed.
6. Bleed air from the system using the bleed bolts (see below). Reinstall the radiator cap once the system is bled and the coolant level is stable.

Bleeding Air from the System

Air pockets in the cooling system will cause hot spots, overheating, and erratic temperature gauge readings. The E07Z engine has bleed bolts on the thermostat housing and sometimes on the water pump outlet to assist with complete air removal.

1. With the engine warm and running, locate the bleed bolt on the thermostat housing.
2. Loosen the bolt slowly — coolant and air will seep out. Keep loosening until only steady coolant flows with no air bubbles, then retighten.
3. If a second bleed bolt is present at the water pump, repeat the process there.
4. Check the coolant level in the radiator and top up if necessary.
5. Replace the radiator cap. Run the engine a few more minutes and verify the temperature gauge reads in the normal range.

Thermostat

The thermostat is housed at the upper water outlet on the engine. It opens at approximately 80°C to allow coolant to flow through the radiator and closes below that temperature to allow the engine to warm up quickly. A stuck-open thermostat will cause the engine to run cold and never reach operating temperature. A stuck-closed thermostat will cause rapid overheating — this is the more dangerous failure mode.

Thermostat replacement requires draining a portion of the coolant and removing the upper hose from the housing. Install a new thermostat with a new gasket or O-ring. Do not reuse the old gasket. Refill and bleed the system after replacement.

Water Pump

The water pump is driven by the timing belt on the E07Z engine, meaning the pump and timing belt are serviced together. If the timing belt is being replaced, replace the water pump at the same time — the additional parts cost is trivial compared to the labor of accessing the timing belt again if the pump fails later.

Signs of a failing water pump include coolant weeping from the weep hole on the pump body, grinding or rumbling noise from the front of the engine, and overheating. A pump that is weeping or making noise must be replaced promptly — failure will destroy the engine.