air in water
 

its a 1.6l with a cheap ebay /aluminum rad about 1.5 years old. only ever used Distilled water and water wetter, and a splash of coolant.

ive been getting a lot of air in my cooling system , consistently.
ive bled it out several times , but the air keeps coming . there are no signs of water leaking from the car. ive doubled up clamp on my hoses and checked every water pipe. its all dry.
right now i have a pressure tester giving the cooling system 20psi of pressure for the last hour .still no leaks.

how does water get in the system?
i would think if there was a way for air to get in . water would come out.
is it the head gasket?

thanks fellas

Check the cap of your overflow tank, the plastic dip-tube inside it, and the rubber hose leading from the radiator neck to it. Also the radiator cap.

During normal operation, the water in your cooling system expands, and the radiator cap allows some of it to vent into the catch tank. This is normal. As the engine cools off and the water contracts, it is supposed to be drawn back into the engine from the catch tank.

Say that there is a hole in the inside of the cap or in the dip tube. No water would escape from the system, but on the cooldown end of this cycle, the engine will suck in some air instead of the water it was supposed to be pulling back in from the tank. It's like trying to drink through a straw with a tiny hole in it.

Joe why would the overflow tank cap matter? Isn't that tank VTA?

Also, OP, OEM clamps are apparently superior to worm gear clamps for rad hoses.

The overflow cap has two separate "sides". It does have a VTA hole on one side (to release air and allow the pressure in the overflow tank to equalize with ambient pressure) however it also provides a sealed path between the rubber hose coming in from the radiator neck and the dip tube that goes down to the bottom of the overflow tank.

If there is a crack, gap, etc., in the cap between the rubber hose and the dip tube, especially one which is on the "inside" side of the cap, then the system will appear to function normally (water which is rejected from the radiator due to expansion will flow into the overflow tank with no leakage) however, during the cooldown phase when the water is contracting, the radiator will suck in air rather than drawing the expelled water back in from the overflow tank.

The same goes for a fissure of the dip tube itself.

The radiator cap is also suspect, as it is possible that it may form a good seal against the radiator neck during warmup and expansion, but leak (admitting air into the radiator) when under the relative vacuum of cooldown.

thanks joe.
i have an aftermarket overflow tank. its a plastic bottle with out a cap ,just a vent hose on top, and the overflow hose on bottom. it seems pretty tight. i got it from a hot rod shop. the hoses are all new including the overflow hose which is larger then stock. i have the wormgear clamps in front of the oem clamps on my heater hoses, cause they did leak a little after i refreshed the car. i replaced every maintenance item inluding the water pump, hoses, gasket, and seals on the entire car just 3 months ago. i had the complete drive train out and refreshed everything but the head gasket.
( it shows no signs of a head gasket failure, including plugs that look very happy.)

but i am suspecting the rad cap , cause the pressure test was left at 20 psi for awhile ,still with out a single drop any where, and the only part of that test absent was the cap.

i had somwhat of that problem too.

under normal driving i didin't had any problem, a bit of a high level in the coolant overflow tank, but that's it.

as soon as i start to beat the car, boost it up, rev it higher in a couple spirited runs, my overflow was spilling coolant everywhere. and my rad level was never full when i checked in the morning.

it was not leaking from anywhere, allways had a super thin coolant smell when i pushed it hard.

it started and gotten way worst within a week.i founded coolant in my catch tank,coolant in my oil while i changed it.

i changed the cap, thermostat, quadruple checked every hoses, and bleed it 15 times with a funnel.

took the engine apart and founded a crack between a valve and the side of the combustion chamber#2

perform a compression test/leak test