Hi everyone first time here
am hoping that someone might be able to help with a problem i have

its a 1996 2.0 ecotec astra sport 96000 miles mk 3
every day or so i have to put 1ltr of water in it,fill expansion tank to level drive car 10 miles or so and most of the water in tank has gone.
when you remove cap water level goes up to 3/4 way up the tank lots of bubbles in water to. car does not overheat temp shows around 90 and when it does go above slightly which isnt very oftern the rad fan comes on as it should.water is going somewhere no leak anywhere no steam nothing out the exhaust

have also noticed that when u start the engine you get a noise like the rad fan makes when its on....but the fan isnt on,dont know where its coming from.also when cold seems to misfire like its not running on all 4 for a few moments then seems ok.
Only had the car 4 wks last owner said he had put an new water pump on it,but she was cheap so think he knew more than he said.

no white stuff under oil cap,but slight stuff on dip stick (light brown)
also EML is on all the time dont know if this is anything to do with above.

seems to drive fine no loss of power just not good that have to put so much water in it all the time...any ideas?