I done some home work yesterday and the only way I can use the small tank that I bought is to find a two way 10 psi pressure relief valve to install on the fitting at the top of the tank. The disadvantage to running an open system is that at 212 degrees the coolant will start to expand and go into the tank. A closed system will let your temps run up to about 260 degrees before it starts to expand. If I can't seperate the systems right, I'm not going to do it. I'll have to buy another tank that has a regular type radiator cap on top or find a two way pressure relief valve, does any body know were I can find a valve like this? I just hate to spend another $125 for another overflow tank. I'd rather be able to use the one that I have.