Running pressure checks can be an accurate way to determine if your Mercury radiator is failing. After all, pressure is the key to an efficient coolant system. Your radiator, if running correctly, will hold pressure steady, which boosts the boiling temperature of the fluid. If properly pressurized, steam bubbles will be prevented and that in turn, makes it easier to keep the engine cooled down. When pressure is running too high in your Sable, the seams in the radiator will split and cracks will appear between the tubes. Too-high pressure levels can be caused by leaks that are letting exhaust into the coolant system through the combustion chamber. Or, the pressure cap might be malfunctioning. You can pressure check the coolant system to determine if there are any leaks. The cap can also be pressure checked to determine if it is performing according to its pressure rating. To do a pressure check, place a coolant system pressure device where the radiator cap is located and then pump it up. If the gauge cannot hold pressure for any length of time (the manual will give you the correct specs on this), then you have a crack somewhere. If you determine that your Mercury radiator must be replaced, then order a new (not reconditioned!) radiator from our site. After installation, take the time to run another pressure check to make sure everything is running to spec.