Nissan skyline r33 owners help!!!!?

check to see if you got any coolant in the oil...or oil in the coolant...if there is than you got a blown head....if not then move on the the radiator...if theres no cracks or signs of leakage then move on to the water pump...if its the water pump it should drip coolant out of the drain hole that its equiped with....if none of that occurs...then it could just be that you filled it up too much and so when the coolant is hot, the coolant overflowed out and then when you checked it, its low...