Most cost guides list four. Here are all eight, with severity ratings, the what-to-do-next for each, and the diagnostic tests a real shop will run before quoting you.
If you have S1, S2, or S5 confirmed, do not keep driving. The cost of a tow is roughly $100. The cost of a warped head from another 50 miles of overheating is $1,000+.
Sweet-smelling, persistent. Coolant is being burned in the combustion chamber and exiting through the exhaust as steam. A puff on cold mornings is condensation and is normal. A constant cloud, especially with a sweet smell, is coolant.
Next step
Confirm with a block test. Do not drive long distances. Catalytic converter damage from coolant is a $1,500 add-on you do not want.
Pull the dipstick. If the oil is the color of a chocolate milkshake (light brown, foamy), coolant is mixing into the engine oil. Running an engine with contaminated oil destroys bearings within hours.
Next step
Tow it. Have the gasket and oil replaced before the engine is run again. If it has been driven this way for weeks, ask the mechanic to check the bearings.
You are topping up the reservoir weekly but cannot find a drip, puddle, or wet spot under the car. The coolant is going somewhere internal: into the cylinders to be burned, or into the oil pan.
Next step
Block test ($30 to $50 chemical kit, or $50 to $100 at a shop). Check the oil. If coolant is in the oil, switch to symptom S2 protocol.
The temperature gauge climbs faster than normal, especially on hills or at idle in traffic. A failing gasket lets combustion gases into the cooling system, which displaces coolant and reduces cooling efficiency.
Next step
Pressure test the cooling system. If pressure rises with the engine running, gases are entering. That is the gasket.
With the engine running and the cap off (cold engine only, never on a hot one), watch the coolant. Bubbles, gurgling, or foam means combustion gases are entering the cooling system. This is one of the most reliable head gasket tests.
Next step
This is essentially a free at-home block test. If you see bubbles, the gasket is the prime suspect.
Coolant or oil seeping from the seam where the cylinder head meets the block. Less common than internal leaks but easier to spot. Often presents as crusty residue or wet streaks down the side of the engine.
Next step
Confirm the leak source by cleaning the area and watching for return. External leaks may respond to a sealer better than internal ones.
If the gasket is leaking between two cylinders, compression bleeds from one to the other. The engine feels rough, especially at idle. An OBD-II scanner usually shows a misfire code (P0301, P0302, etc.) on the affected cylinder.
Next step
Compression test. Adjacent low-compression cylinders are a strong indicator of head gasket failure between them.
Failed compression on one or two cylinders means the engine is making 75 to 90% of its normal power. Less obvious than a misfire but cumulative with other symptoms. Often the last thing people notice.
Next step
Combine with other symptoms. Power loss alone is not diagnostic, but with white smoke or coolant loss it confirms the picture.
Question we get most
Short answer: no. Long answer: it depends on what is failing.
A few miles, slow, with the heater on full blast (it pulls heat out of the cooling system) is sometimes survivable. You will probably make the symptoms worse.
Risky. Coolant loss accelerates as the leak grows. Overheating warps the head and converts a $2,000 repair into a $4,000 one.
Will likely destroy the engine. Combustion gases shred the bearings, the head warps, and the catalytic converter is poisoned by coolant. Tow it.
How shops confirm it
Block test (combustion leak test)
$30 - $50 DIY, $50 - $100 at shopChemical kit pulls air from the radiator into a blue fluid. If combustion gases are present, the fluid turns yellow. The most reliable single test.
Compression test
$50 - $100Measures pressure in each cylinder. Two adjacent low cylinders point to a head gasket leak between them.
Coolant pressure test
$50 - $100Pressurises the cooling system. Watches for pressure loss or for pressure to build with the engine running (combustion gases entering).
Visual inspection
Included in diagChecks for external coolant or oil leaks at the head-to-block seam. Also looks at oil cap and dipstick for milkshake.
If a shop tells you the head gasket is blown without running at least two of these tests, ask which one they ran. A guess based on symptoms alone is not a diagnosis.