Engine over heating

It sounds like the crack in the head is in a location that is allowing coolant to escape. Cracked heads can also allow oil to leak, provide poor compression, cause smoke and make the engine seem like it is not firing all cylinders (called "missing").

By removing the thermostat, you are allowing the coolant to circulate freely between the engine and radiator, instead waiting for the temperature to rise in the engine behind the thermostat. This reduces the operating temperature of the engine and lowers the cooling system pressure. Lowering the pressure is what you're after so the coolant will not be trying to escape.

You may be overheating because the coolant level in the engine and radiator is too low and not getting proper circulation from one to the other. The thermostat allows the engine to stay hot - and make heat for the cabin. Removing the thermostat generally makes the engine run cooler.

First, check the coolant level by removing the cap completely from the radiator filler neck when the engine is cold. The coolant should be an inch (or 2 at the most) below the top of the filler neck of the radiator when warm, but may be 2 or 3 inches below when cold. If you cannot see the coolant level in the radiator, add a 50% mixture or water and antifreeze directly to the radiator until it is 3 or 4 inches below the top of the filler neck. Start the engine, set the heater to hot and high fan and wait for the engine to warm up. Check the coolant level in the radiator regularly while the engine is running. Watch the temperature gauge if your car has one. Add additional amounts of the 50% coolant and water mixture as needed - but only to 3 or 4 inches below the top of the filler neck. Once the engine is warmed up completely, top off the coolant level to withing 1 or 2 inches of the top of the filler neck.

If you're loosing coolant, try loosening the radiator cap (wait until the engine is cold first!). This will bring the pressure in the system down to 0. With 0 pressure, the coolant won't be trying to squirt through the crack. You will need to make sure that the temperature of the engine does not exceed 212F (100C) otherwise it boil over and can result in even more damage to the engine. Check your oil level and coolant level regularly. The coolant reservoir will no longer be the place to check the level - as when the coolant overflows - it will do so to the ground because the radiator cap is loosened.

If the oil is milky, then coolant is leaking into the crankcase and is contaminating the oil. Water is not a good lubricant and will cause catastrophic failure if not repaired. Needless to say, you should have this fixed or replaced as soon as possible.

I hope this helps and good luck!