Where is the coolant going?

[tkruger]

1987 4.3 liter. I always have enough coolant in the radiator itself when I check it the old fashion way by taking the cap off (only when cold for multiple hours).

I fill the coolant jug when the motor is cold to the cold full line. When hot it does rise above that point but not allot. Over the time of a few weeks the level is only enough to cover the hose at the bottom of the tank when cold. I can run with this little bit of coolant in the tank without the radiator itself ever getting being low when checked by removing the cap. There is no white residue on the hoses going to or from the radiator. I do not get white smoke out of the tail pipe. There is a puff of darker exhaust when first starting the vehicle after it has been sitting (my mechanic said that was nothing to worry over). There is no residue on the windshield after the defroster is used and the heater core does not appear to be leaking. Only issue that I can see is there is only one bolt holding the tank in-place, one of them is missing.

 

[ssn696]

Check for a crack or broken cap on the coolant tank. On an 82 Chevy truck, about 15 years ago, there was a crack on the back of the plastic coolant overflow tank. No drips, but coolant kept disappearing. I'd fill the radiator and top off the overflow tank, but then a few weeks later, the radiator was low again. Turns out the coolant was pushed into the overflow tank when hot, the water would evaporate, and then air would suck back into the radiator through the crack in the tank when the engine cooled.

This may not be our problem, but it might explain the disappearing coolant..