White smoke from the exhaust
Milky or frothy oil on the dipstick or under the oil cap
Coolant loss with no visible external leak
Engine overheating
Bubbles in the radiator or coolant reservoir
Rough idle or engine misfires
Loss of engine power
Sweet smell from the exhaust
Contaminated coolant that looks oily or dirty
Coolant in the oil or oil in the coolant
Engine starting problems
Persistent check engine light
Compression loss in one or more cylinders
Unexplained pressure in the cooling system
Spark plugs that look steam-cleaned or damaged