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1995 Geo Metro losing water

1995 Geo Metro with new radiator, thermostat and coolant temperature switch loses water. The heater core is good, pressure test reveals no leaks, no presence of water in the oil, and a dye test reveals no leaks. Need to add coolant every couple of days. Any thoughts?

If there’s no leak or pressure loss when you’re testing the system at rest (i.e. with the engine not running) then is must be something that leaks while the engine is running. The most likely explanation is a water pump shaft seal that leaks while it is rotating, but not when it’s at rest. Did you check for evidence of past coolant leakage at the weep hole?

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How long ago were all of those cooling system components replaced? Maybe there was just a lot of air left in the system that’s still working its way out?

Bad head gasket maybe. Test kits are available for that.

How 'bout the radiator cap?

When you pressure test a cooling system, the radiator cap is removed. So if the radiator cap leaks, it’s not detected.

If it hasn’t been replaced, replace it.

Tester

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Thanks to everyone for the prompt and knowledgeable replies. Unfortunately, everything that’s been mentioned is something we’ve already explored and pursued. It’s really perplexing. Again … we appreciate all comments and assistance.

That is what happens when you don’t tell everything that has been tried before you ask for help. Have you tried a hot pressure test?

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Idle the engine until it reaches operating temperature, then while a helper briefly increases the idle rpm to 1500 or so, ask your shop tech to look here and there & under the car for any signs coolant leaking. Especially in the water pump area. If no leaks are evident the coolant must be leaking into the insides of engine, most likely an intake manifold or head gasket.

That said it is pretty common to have a water pump leak that leaks onto something hot enough to evaporate before dripping onto the ground.

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I appreciate the time you took to comment. You’ll see in our original post that we did, in fact, state that a pressure test was conducted and revealed no leaks.

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Good info and advice, George. Thanks!

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I did not ask you if you did a pressure test, I asked you if you did a HOT pressure test, sometime an engine will not leak cold but will leak under pressure when it is at full operating pressure and temperature.

You’re right. I was not clear. But, yes … indeed, we conducted the pressure test with the vehicle at operating temp/pressure. Any additional hints or clues would be appreciated. Thank you.

Remove spark plugs, is one of them especially clean? Suspect a coolant leak into that cylinder. Confirm with a fiber optic camera. I am not at all familiar with Geo metro engines but some engines can leak coolant into an intake manifold passage into a cylinder without a head gasket problem. Have you done a compression test?

Good info! Thanks!! And our mechanic did not perform a compression test, so I jumped on him for that.