thats an interesting one.
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what was the water temp gauge reading during the journey? if theres coolant in the system it would probably show overheating.
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if theres no fluid presumably it shows the air temp in the pipes, which may be less?
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first id suggest looking at the filler cap for mayonaise.
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if the head gasket has gone its possible coolant was being burnt in the cylinders.
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also if it wasnt the cause, possibly overheating the engine might cause the head gasket to go.
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then id just fill the system up with water, try to measure out how much you are putting into the system.
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if its not much then theres coolant in the system and you can relax somewhat.
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if you have to put a lot in, see if anything is leaking out of the system.
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if it does thats the first point of call, fix the leak.
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after that drain the system.
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open the bleed valves, one under the plastic radiator cover
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(passenger side) and the other on the cabin bulkhead by the clutch reservior.
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reach underneath the bumper on the drivers side, and turn the butterfly screw in the bottom corner of the radiator and let everything drain out, helps to jack the rear of the car up too.
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once everything is out, keep running water through the system until what comes out is clear.
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close the system off and fill it with water.
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add a coolant system flush
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(available from halford etc), and run the engine up.
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at this point if the engine has a problem, it will probably be noticable.
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drain the water, close the system off and fill with toyota long life red coolant.
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bleed the system using the bleed valves.
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hth