White exhaust smoke that continues after startup
Sweet smell from the exhaust
Engine overheating
Coolant loss with no visible external leak
Milky or frothy oil on the dipstick or oil cap
Bubbles in the radiator or coolant reservoir
Rough idle or engine misfires
Loss of engine power
Coolant in the spark plug holes
Engine oil in the coolant
Hard starting or no-start condition
Compression test showing low compression in one or more cylinders
Leak-down test showing air escaping into the cooling system
Constantly pressurized cooling system shortly after startup
Repeatedly blown radiator hoses or coolant overflow
Check engine light with misfire or overheating codes