White exhaust smoke, especially after warm-up
Sweet smell from the exhaust
Engine overheating repeatedly
Coolant level dropping with no visible external leak
Milky or frothy oil on the dipstick or under the oil cap
Oil in the coolant reservoir
Bubbles in the radiator or coolant reservoir
Combustion gases in the cooling system
Rough idle or engine misfire
Loss of engine power
Hard starting or no-start condition
Spark plugs that look steam-cleaned or unusually fouled
Coolant leaking from the tailpipe
Frequent need to top off coolant
Compression loss in one or more cylinders
Low cylinder leak-down test results
Engine oil contaminated with coolant
Radiator hoses becoming very hard soon after startup
Heater blowing cold air when engine is hot
Check engine light with misfire or coolant-related codes