1.1 Underfacia arrangement of the blower unit, evaporator, and heater unit (LHD model shown, RHD is a mirror image)
1 General information
All vehicles covered by this manual employ a pressurised engine cooling system with thermostatically-controlled coolant circulation. An impeller type coolant pump mounted on the front of the block pumps coolant through the engine. The coolant flows around each cylinder and toward the rear of the engine. Cast-in coolant passages direct coolant around the intake and exhaust ports, near the spark plug areas and in proximity to the exhaust valve guides.
A wax-pellet type thermostat is located in the thermostat housing at the transmission end of the engine (Non-VVT-i engines) or on the front face of the engine block (VVT-i engines). During warm-up, the closed thermostat prevents coolant from circulating through the radiator. When the engine reaches normal operating temperature, the thermostat opens and allows hot coolant to travel through the radiator, where it is cooled before returning to the engine.
The cooling system is sealed by a pressure-type radiator cap. This raises the boiling point of the coolant, and the higher boiling point of the coolant increases the cooling efficiency of the radiator. If the system pressure exceeds the cap pressure-relief value, the excess pressure in the system forces the spring-loaded valve inside the cap off its seat and allows the coolant to escape through the overflow tube into a coolant reservoir. When the system cools, the excess coolant is automatically drawn from the reservoir back into the radiator.
The coolant reservoir does double duty as both the point at which fresh coolant is added to the cooling system to maintain the proper fluid level and as a holding tank for overheated coolant.
This type of cooling system is known as a closed design because coolant that escapes past the pressure cap is saved and re-used.
The heating system consists of a blower fan and heater matrix located within the heater box under the facia, the inlet and outlet hoses connecting the heater matrix to the engine cooling system and the heater/air conditioning control panel on the facia (see illustration). Engine coolant is circulated through the heater matrix. When the heater mode is activated, a flap door opens to expose the heater box to the passenger compartment. A fan switch on the control head activates the blower motor, which forces air through the matrix, heating the air.
The air conditioning system consists of a condenser mounted in front of the radiator, an evaporator mounted adjacent to the heater matrix, a compressor mounted on the engine, a receiver/drier which contains a high pressure relief valve and the plumbing connecting all of the above.
2.1 Use a hydrometer to test the strength of the antifreeze mixture
A blower fan forces the warmer air of the passenger compartment through the evaporator matrix (sort of a radiator-inreverse), transferring the heat from the air to the refrigerant. The liquid refrigerant boils off into low pressure vapour, taking the heat with it when it leaves the evaporator. The compressor keeps refrigerant circulating through the system, pumping the warmed refrigerant through the condenser where it is cooled and then circulated back to the evaporator.
2 Antifreeze/coolant -
J A Warning: Do not allow antifreeze to come in contact with your skin ■ or painted surfaces of the vehicle.
Rinse off spills immediately with plenty of water. Antifreeze is highly toxic if ingested. Never leave antifreeze lying around in an open container or in puddles on the floor; children and pets are attracted by its sweet smell and may drink it. Check with local authorities about disposing of used antifreeze. Many communities have collection centres which will see that antifreeze is disposed of safely. Never dump used antifreeze on the ground or into drains.
The cooling system should be filled with a water/ethylene-glycol based antifreeze solution, which will prevent freezing down to at least -30° C, or lower if local climate requires it. It also provides protection against corrosion and increases the coolant boiling point.
The cooling system should be drained, flushed and refilled regularly (see Chapter 1). The use of antifreeze solutions for extended periods is likely to cause damage and encourage the formation of rust and scale in the system. If your tap water is 'hard', ie, contains a lot of dissolved minerals, use distilled water with the antifreeze.
Before adding antifreeze to the system, check all hose connections, because antifreeze tends to search out and leak through very minute openings. Engines do not normally consume coolant. Therefore, if the level goes down, find the cause and correct it.
The exact mixture of antifreeze-to-water you should use depends on the relative weather conditions. The mixture should contain at least 50 percent antifreeze, but should never contain more than 70 percent antifreeze. Consult the mixture ratio chart on the antifreeze container before adding coolant. Hydrometers are available at most motor parts/accessory stores to test the ratio of antifreeze to water (see illustration). Use antifreeze which meets the vehicle manufacturer's specifications. Note: The antifreeze available from a Toyota dealer is ready-mixed and doesn't require further dilution.
3 Thermostat -
testing and renewal
A Warning: Do not attempt to fi\ remove the radiator cap, coolant or thermostat until the engine has cooled completely.
1 Before assuming the thermostat is responsible for a cooling system problem, check the coolant level (Chapter 1), drivebelt tension (Chapter 1) and temperature gauge (or light) operation.
2 If the engine takes a long time to warm-up (as indicated by the temperature gauge or heater operation), the thermostat is probably stuck open. Renew the thermostat.
3 If the engine runs hot, use your hand to check the temperature of the radiator top hose. If the hose is not hot, but the engine is, the thermostat is probably stuck in the closed position, preventing the coolant inside the engine from travelling through the radiator. Renew the thermostat.
Caution: Do not drive the vehicle without a thermostat. The engine management ECM may stay in open loop and emissions and fuel economy will suffer.
4 If the radiator top hose is hot, it means that the coolant is flowing and the thermostat is open. Consult the Fault finding Section at the rear of this manual for further diagnosis.
5 Drain the coolant from the radiator (see Chapter 1).
6 Disconnect the cooling fan temperature switch connector from the thermostat cover located at the left end of the cylinder head (see illustration).
7 Detach the thermostat cover from the housing. Be prepared for some coolant to spill as the gasket seal is broken. The radiator hose can be left attached to the cover, unless the cover itself is to be renewed.
8 Remove the thermostat, noting the direction in which it was fitted in the cover or housing, and thoroughly clean the sealing surfaces (see illustration).
9 Fit a new gasket onto the thermostat (see illustration). Make sure it is evenly fitted all the way around.
10 On 4A-FE engines, install the thermostat and the cover, positioning the jiggle pin at the highest point. On 4E-FE engines, position the thermostat in the cover with the jiggle pin aligned with the raised projection on the cover, then install the cover and thermostat.
11 Tighten the cover fasteners to the torque listed in this Chapter's Specifications and reinstall the remaining components in the reverse order of removal.
12 Remove the alternator as described in Chapter 5A.
3.14 Discard the thermostat seal, and fit a new one
13 Undo the two nuts and remove the thermostat cover (see illustration).
14 Remove the thermostat. Discard the seal, a new one must be fitted (see illustration).
15 Fit a new seal to the thermostat, and fit it into position on the engine block, with the jiggle pin at the 12 o'clock position (see illustration).
16 Refit the thermostat cover and tighten the nuts to the specified torque.
17 Refit the alternator as described in Chapter 5A.
18 Refill the cooling system (see Chapter 1), run the engine and check for leaks and proper operation.
4 Engine cooling fan and relay 1
- testing and renewal ^
Warning: To avoid possible injury, keep clear of the fan blades, as they may start turning at any time.
Note: No cooling fan temperature switch is fitted to VVT-i engines. The coolant temperature is monitored by the engine management ECM via the coolant temperature sensor, and the fans are operated by energising the cooling fan relay(s). 1 If the radiator fan won't turn off when the engine is cool, disconnect the wiring
3.15 Fit the thermostat with the jiggle pin at the 12 o'clock position
4.6 Test the fan relay (Nippondenso). With no voltage applied, there should be continuity between 1 and 2, and 3 and 4 - with voltage applied across 1 and 2, there should be NO continuity between 3 and 4
On Bosch relays, disregard the terminal numbers, test it just like this Nippondenso relay
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