1996 Toyota Tarago radiator Spitting out water

Replaced new thermostat and then car started to spit water out of the radiator but only when you turned the car off, temperature needle doesn't move all the time the only time the needle did move up to the H the radiator was fine wasn't hot didn't need water. I have no oil or fuel running round in my water, no milkshakey look under my oil cap no noises comming from under my bonet. Thought it was a faulty thermostat so removed that and it's still doing it. There is no leaks or water on the ground at all it only spits out about 1 liter of water and only when you pull up and turn the motor off.