Antifreeze

[foxi]

If a Car engine gets hot, boils the Coolant & blows it out of the filler cap, what should you do next? Should you allow the engine to cool down then refill it with the correct mix of antifreeze/water, or immediately fill up the still hot running engine with just plain cold water?

[NORMANTHEDOG]

first of all you really need to find out why in this weather it overheated in the first place, but leave it for a little while before refilling with water,and because of the weather now put some anti freeze in with it,orb it could freeze the block up.

[dm1982]

either an airlock or the head gasket is gone and pushing pressure through the cooling system

[rov1200]

It sounds as if you have a blocked radiator. As a test you could undo the bottom hose and pour water through it before wasting your money on anti-freeze at this stage.

[TWR]

Did the car have antifreeze in the system when it boiled? If it had not the coolant has frozen.

[Nkakamasembe]

Allow me to give answers to your questions.
1.Let the engine cool, fill up with coolant if you need to bleed the system do so.
2. Because the engine is so hot attempting to fill up immediately with hot water while engine is running will not work.

[chas2008]

once cooled down you could fill up with cold water , really depends on how much coolant was lost.

But you really need to get to the cause of the problem before it becomes terminal....ie, frozen.headgasket,waterpump, stat etc.