White smoke from the exhaust
Milky or frothy oil on the dipstick or under the oil cap
Coolant disappearing with no visible leak
Engine overheating repeatedly
Bubbling in the radiator or coolant reservoir
Rough idle or engine misfiring
Loss of engine power
Sweet smell from the exhaust
Contaminated coolant with oil residue
Hard starting or poor compression
Check engine light on
Visible external coolant or oil leaks near the head gasket area