Some suggestions:-
- Open the oil filler cap and look insdie and under the cap... If the oil does not look 'Milky'... this is good.
- If the coolant does not look 'Milky' and/or discoloured/dirty... this is good.
- Car not overheating, this is good.
- Can't see any water on the ground after a drive(So car is hot/warm..), this is good as well.
- Start the car, open bonnet and squeazy the hoses to see if you have pressure(Carefull they can be very hot so use a towel..) No pressure=bad
... you lave a leak somewhere. - Check under you dash so any wet patches as the heater core could have a spilt.
The one thing you cannot check is the inlet manifold gasket as the water will be burnt in the combustion chamber as part of the air induction, no evidence.
Good luck...
