Is it true that water must be slightly warm when pouring it into an overheated radiator?

Question

Will cold water crack your car's cylinder head?

Answer 1

as long as the engine is running while you are adding water to it (that way it gets warmed and circulates through the engine), it won't really matter. If you add water (even warm water) to an overheated vehicle, without the vehicle running, one of the biggest things that you may end up having to do, is jump back as it may overflow after getting heated quickly by the already hot liquid that may be in your radiator. The best thing that you can do is allow the vehicle to cool down, start your engine and add your coolant to it, after that you need to find out why it overheated, is your thermostat stuck closed/did your water pump quit working ... plenty of things can cause your vehicle to overheat, and needs to be checked out by a mechanic

Answer 2

Better yet, wait for the radiator to cool down. Cold water can indeed crack a hot engine block.

Answer 3

it won't crack the cylinder, but it might damage the radiator further. Best just to let the whole engine cool and then fill it up.

Cold water won't crack an engine, consider when your engine is hot and you drive through a deep puddle in the winter time. You just leave a cloud of steam behind you.

Answer 4

The best thing to do is to wait until the radiator cools down, it is almost impossible to get cold water into your actual engine so that should not be a problem.

Answer 5

If you are adding just a gallon its no problem but if your radiator has lost all of its water and anitfreeze wait till engine cools down or you will cause radiator damage.

Answer 6

Let the engine cool down,even if you put warm water in it may boil and scald you.