How do I know if I need to replace the head gasket on my car?

If you are loosing coolant with no apparent leak, sweet smell at the exhaust, coolant mixed with the oil, air bubbles coming out of the radiator, (engine running, cap off), foamy substance on the underside of the oil cap. All or some of these is a sign of a blown head gasket. To verify this perform a compression test on all cylinders. Low compression on one or more cylinders is suspect. Warning: Continuing to drive this vehicle in this condition will result in severe engine damage.