DESCRIPTIONThis engine utilizes a pressurized water forced circulation cooling system which includes a thermostatequipped with a by–pass valve mounted on the inlet side.The cooling system is composed of the water jacket (inside the cylinder block and cylinder head), radiator,water pump, thermostat, cooling fan, hoses and other components.

OPERATION

CO–2–COOLING SYSTEM Description, Operation

Coolant which is heated in the water jacket ispumped to the radiator, through which a cooling fanblows air to cool the coolant as it passes through.Coolant which has been cooled is then sent back tothe engine by the water pump, where it cools the en-gine.The water jacket is a network of channels in the shellof the cylinder block and cylinder head throughwhich coolant passes. It is designed to provide ade-quate cooling of the cylinders and combustionchambers which become hottest part during engineoperation.

RADIATORThe radiator performs the function of cooling thecoolant which has passed through the water jacketand become hot, and is mounted in the front of thevehicle. The radiator consists of an upper tank andlower tank, and a core which connects the twotanks.The upper tank contains the inlet for coolant fromthe water jacket and the filler inlet. It also has a hoseattached through which excess coolant or steamcan flow. The lower tank contains the outlet for cool-ant and the drain cock.The core contains many tubes through which cool-ant flow from the upper tank to the lower tank as wellas cooling fins which radiate heat away from thecoolant in the tubes. The air pulled through the ra-diator by the cooling fan, as well as the wind gener-ated by the vehicle’s travel, passes through the ra-diator, cooling it. Models with automatictransmission include an automatic transmissionfluid cooler built into the lower tank of the radiator.A cooling fan is mounted behind radiator to assistthe flow of air through the radiator. When the coolanttemperature is low, the fan operates slowly to helpthe engine warm up, and when the coolant tempera-ture becomes high, the fan speed is increased toprovide the air flow required for cooling.

RESERVOIR TANK CAPThe reservoir tank cap is a pressure type cap whichseals the radiator, resulting in pressurization of theradiator as the coolant expands. The pressurizationprevents the coolant from boiling even when thecoolant temperature exceeds 100°C.A relief valve (pressurization valve) and a vacuumvalve (negative pressure valve)are built into the res-ervoir tank cap. The relief valve opens and lets

steam escape through the overflow pipe when thepressure generated inside the cooling system ex-ceeds the limit (coolant temperature: 110–120°C,230–248°F, pressure; 59–103 kPa, 0.60–1.05 kgf/cm2, 8.5–14.9 psi).The vacuum valve opens to alleviate the vacuumwhich develops in the cooling system after the en-gine is stopped and the coolant temperature drops.

RESERVOIR TANKThe purpose of the reservoir tank is to catch coolantoverflow created by volumetric expansion when thecoolant temperature increases. The cap of the res-ervoir tank is a pressure type cap which prevents de-terioration of the year–round coolant caused bycontact with atmospheric air, increases vaporizationperformance and reduces loss of coolant volume.

WATER PUMPThe water pump is mounted on the front of the cylin-der block and driven by the reverse side of the timingbelt.

THERMOSTATThe thermostat has a wax type by–pass valve andis mounted in the water inlet housing.The thermostat begins to open at the temperatureof 82°C (180°F).When the coolant temperature is low, the valvecloses to prevent coolant flow to the radiator, thuspermitting the engine to warm up rapidly. When theby–pass valve opens the by–pass circuit, the en-gine coolant continues to circulate inside the en-gine, quickly and uniformly warming up to the ap-propriate temperature.When the coolant temperature is high, the valveopens and coolant flows to the radiator where it iscooled. When the wax inside the thermostat isheated, it expands and thus creates pressure whichoverpowers the force of the spring which keeps thevalve closed. When the wax cools, its contractioncauses the force of the spring to take effect oncemore, closing the valve.

ELECTRIC COOLING FANThis vehicle is equipped with two electric coolingfans to help cool the radiator. When the air condi-tioner compressor is operating, the fans operateslowly, and when the radiator temperature in-creases, the fans operate rapidly to help cool the en-gine.

–COOLING SYSTEM OperationCO–3