Engine Cooling problem
1998 Other Mitsubishi Models 6 cyl Front Wheel Drive Manual 105000 miles

I have a mitsibushi 98 3000GT which has a strange problem that no mechanic seems to solve.
If i go for long distances for more than 30 miles or if i go over 50 mph for 5 mins the engine temperature gauge shoots up and the oil level falls down and if i continue driving the coolant shoots out and the car stalls.
i tried various mechanics who seem to be charging me for fixing a small leak here and there and each of them claiming that the car has passed a pressure test, but right after i take the car out of the shop the same problem appears.
I have all the fluids full and ther are no leaks in the cooling circuit..but still this happens.

Please Help!