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Cooling & heating
Pictures & diagrams ...
Blower for rear climate control (J Corfield #24)
Blower for rear climate control (J Corfield #25)
Cooling system. (Oblsud)
Radiator filler neck (Ray Woolmer)
Radiators, horizontal. (Oblsud)
Radiators, horizontal. (Oblsud)
Heater ducts inside dashboard. (Oblsud)
Heater plumbing. (Oblsud)
Heaters. (Oblsud)
Water pump and viscous fan mounting. (Oblsud)
The cooling system can fail and cause you a lot of inconvenience and some expensive repairs. The worst case scenario is a warped cylinder head which you will pay £400 to £600 to get fixed.
The system has some unusual features which are worth trying to understand so you can do enough preventative maintenance and spot early symptoms of any failure - therefore limiting the inconvenience and cost.
System description
For completeness, I'll start at the beginning:The crucial function of the system is to maintain, particularly the head/top of, the engine at roughly the correct working temperature. Not just for efficiency.Too cold and the oil will not lubricate properly - as unfortunately happens every time you start from cold.Too hot will cause the head gasket to break apart and the head itself to warp.
The heat comes from the chemical energy in the fuel. Anything that is not converted into shaft horsepower has to be got rid of as waste heat, ultimately into the air. This so-called "waste" heat is unavoidable. Engine designers have to allow for it. It's not because the engine is running badly, although it can slightly increase for that reason.
The heat is removed in three stages. A liquid coolant is heated inside the top of the engine. It is circulated by the water pump into the radiator. The radiator transfers the heat to the nearby air - air which is moved on by the motion of the vehicle and, when necessary, by fans.
So that the engine does not run too cold there is a thermostat. This is a temperature sensitive valve which prevents the coolant being pumped through the main radiator(s) when it is below the design temperature.
Unusual features
- If you have automatic transmission then there is an additional horizontal radiator in front of the other, upright, one, and the transmission oil is cooled by passing through a coil in the L/H (cool) tank of the upright radiator.
- The thermostat is at the bottom of the engine, where the bottom hose is connected.
- The water pump is driven off the back of the timing belt.
- The fan between the radiator and the engine is mounted on a belt-driven pulley via a temperature sensitive "viscous coupling" which hardly turns the fan until a certain temperature is reached.
- The sender for the temperature gauge is well-placed in the head just below the inlet manifold, but the indicator on the dash has a marked "flat spot" which means that it hardly moves unless there is overheating. It does not tell you much about the normal variations that occur.
- The radiator cap is not on top of the radiator.
- The coolant expansion tank is so placed that you can't easily see how full it is.
- There are two heater matrices in the system, for the front and rear cabin heaters. Coolant always flows through the rear one but there is a valve for the front one.
What goes wrong
All of the engine's waste heat will not be transferred to the nearby air if either there is excessive waste heat or the 3-stage transfer process is not working well enough, coolant being heated, circulated, and cooled by air moving through the radiator. Possible root causes of trouble are in bold.- Excessive waste heat would usually be because the engine is very badly tuned and there would be noticeable loss of power - but severe overheating from other causes can also cause loss of power.
- Insufficent coolant will mean that there is none in the top of the engine to be heated. Coolant could have been lost from a simple leak from a radiator, radiator cap, hose, joint, etc, or because the recovery system for sucking coolant back from the expansion tank is faulty - a water or air leak, especially in the radiator cap, or a blockage.
But severe overheating from another cause could have made it vent as steam via the radiator cap functioning as a pressure-relief valve. A head gasket can fail, either on its own or as a result of overheating, which then allows combustion pressure into the coolant system and drives the coolant out, either through the radiator cap or any other weak point - run with the cap off and you will see the unusual bubbling and coolant motion, "like a volcano". - Insufficent coolant circulation can be caused by sludge, airlocks, thermostat* not opening, or much less likely, a failing water pump. A notable number of failures have occured soon after major maintenance has been done - a time when airlocks may not have cleared from the system properly.
- Insufficient airflow at the radiator can be caused by clogged airways between the fins, failed fan/viscous coupling, damaged or missing ducting around the fan and radiator, or possibly an obstruction in the air route to the radiator, e.g. the number plate or some foreign object.
*N.B. Thermostats can also get stuck open, causing the engine to run too cool. Spotting the symptoms
Low coolant level and head gasket failure are like chicken and egg. Either can cause the other. Head gaskets do not last for ever even in a perfectly-running Toyota. Coolant levels do drop - no amount of maintenance can prevent old radiators and hoses from springing leaks, and frequently checking the water level by removing the radiator cap can cause the seal in the cap to deteriorate and prevent coolant recovery from the expansion tank. Add to that the possibility of unpredictable failure of the thermostat or viscous fan coupling and you wonder what to do. The key is to monitor the head temperature. Fit a better gauge or modify the present one, and even fit an alarm to sound when a critical temperature is reached. Unusual indications on the gauge will alert you to all these things that can go wrong and allow you to prevent the problem escalating - though if a head gasket simply dies there's no escaping replacing it, but you can probably save the head from warping badly.
Water level
The water level is supposed to be checked in the expansion bottle, the white plastic tank under the passenger seat, and topped up there to between the marks on its side. But this is only reliable if the radiator cap is working properly - sucking coolant back into the radiator as the system cools and experience shows that the radiator cap is a frequent cause of failure. Therefore it is best to also let the engine cool (overnight) and take off the radiator cap. the water should be up to the neck. If it isn't (but there is water in the expansion tank) probably the radiator cap has failed, or you've got a leak somewhere along the pipe preventing coolant being sucked back through it from the expansion tank.
Doing this regularly is vital, at least monthly, preferably weekly, depending on how much the car is used. The inconvenient access to the engine bay can be off-putting so work out a good technique - it's worth it.
At least once run the engine with the radiator cap off and observe the behaviour of the coolant. Should you ever suspect the head gasket you will then know whether the bubbling etc is "normal" or not.
Emptying the coolant from the system.
There's a tap at the bottom of the radiator, it's the front drivers side of it. Automatics also have another radiator under the floor at the front, there's a tap at the front of it also. The block has a drain, but don't risk trying to undo it, 90% will drain through the rad drain anyway. Thorough flushing is wise, several times, running the engine up to temperature between each flush. Use good flushing chemicals once as per instructions. Combine this with checking/modifying/replacing your thermostat.
To refill, turn the heater on, and fill very slowly through the rad cap. When full, run the engine for a bit, then recheck. Then put on the cap. With the heater the system holds 7.1 litres.
Improvements to the system.
You will find references to these elswhere.- Fit the latest Toyota radiator cap.
- Improve the temperature indication.
- Modifed thermostat.
- Replace viscous-coupled fan with an electric one.
Dave Mason, editor, Sep 2002