partially-full radiator

my coolant has been dissapearing. i noticed however that if i let it get maybe 2 or 3 inches down from the radiator cap opening when it is cold, it will maintain that level and i dont have to add coolant. could the culprit be a leaky hose to the overflow reservoir or a cracked reservoir? i am worried that perhaps if i let it stay low in the radiator that the top portion of the inside of the radiator above the water might corrode? i wouldnt think it would since the outside surfaces don't and i figure the inside is the same material as the outside, but does anyone know of oxidation occuring due to this?

well what kind of vehicle are we talking here ?

and does it have a radiator fluid recovery tank ?


if not then it is normal to have air space about 2 inches from the top of the radiator when it is cooled off

water expands when it is hot

it is impossible to keep the radiator full when it has cooled off, the water shrinks

this is how it always was in the years before coolant recovery tanks


good luck

Randy78 is correct. Cars without recovery tanks will be low when cold.

However, if you have a closed system recovery tank it is not good that your system is low when cold. This can allow air into the system and cause cavitation on the top side of the engine. That is why the closed system recovery tank was invented. It allows for expansion of the fluids and then sucks them back in as the engine cools thus keeping it full with no air cavitation.

If you have the closed system, you could have a leaky recovery tank, bad radiator cap, bad return hose OR another leak in the engine somewhere that is sucking air back in ahead of the cap or leaking coolant and creating it's own water shortage.

well, i dont think i have to worry about air in the intake, since it's a 4.3 in a full-size pickup truck, so even though it's low, the level in the radiator is still higher than the motor. i figured it was ok, since i have seen many cars that just have a tube that dumps overflow on the ground, so the cold coolant level in those cars naturally would be a few inches lower than the top of the radiator