Which Correct Radiator Level?

[Fernando Mendes]

TM9-801 GMC CCKW WWII Truck,pages 41and 42.
"c.Cooling system
(b)FILLING RADIATOR.Vehicle should be standing on fairly level ground starting to fill radiator.If system is empty ,fill radiator until liquid can be seen through filler neck.If the system is filled with COLD liquid,the thermostat will close even though the engine is warm.This action may trap air in cylinder block and head.The trapped air will leak through thermostat vent hole,thereby lowering liquid level in radiator.Additional coolant should then be slowly added until no further air bubbles are noticed.This method should be used if more than two quarts are necessary to refill radiator.Always fill radiator untill liquid is visible through neck.If engine is COLD,a loss of approximately one quart will result.If engine is WARM no appreciable loss will be noticed.
©USE OF ANTIFREEZE SOLUTION.Do not overfill radiator when antifreeze solutions are used.Normal expansion of heated water causes level to rise.When engine is stopped and water cools,contraction of liquid lowers level.It is this apparent low level which might indicate the need of additional fluid.Water in system should be hot before any check of level is made."

[austinsailor]

It should be noted that if the engine is real hot, adding cold water can crack the block. So, if it's low due to over heating, either allow it to cool first, or VERY slowly add your cold liquid, allowing it to mix with the hot as it circulates. If it has boiled dry, never add anything until it's cooled.

 

There have been many blocks cracked by adding cold water to an overheated engine.

[Fernando Mendes]

It should be noted that if the engine is real hot, adding cold water can crack the block. So, if it's low due to over heating, either allow it to cool first, or VERY slowly add your cold liquid, allowing it to mix with the hot as it circulates. If it has boiled dry, never add anything until it's cooled.

 

There have been many blocks cracked by adding cold water to an overheated engine.

Yes,never put cold water when the engine temperature is above 200ºF or 93ºC.