Hearing from the mechanic that their car has a blown head gasket is every driver’s worst nightmare. Depending on the type of car, it may cost more than $1,000 to replace the head gasket. Before spending that kind of money, drivers should perform their own diagnosis to determine if they really have a blown head gasket. This article reveals seven telltale signs that a car has a blown head gasket.
The head gasket, located between the engine block and cylinder head, is an essential component in modern automotive engines, designed to prevent combustion gases, oil, and coolant from leaking. The head gasket keeps these elements in their respective passages, allowing for optimal engine performance. Head gaskets can fail or “blow” when the engine overheats or from regular usage. If you think your car has a blown head gasket, you should look for the following seven signs.
1) Bubbles in radiator
One sign of a blown head gasket is bubbles in the radiator. To see if your radiator is bubbling, wait for your car’s engine to completely cool off — usually about two hours after driving — and carefully remove the radiator cap with a rag or towel. Now crank your car and observe the coolant as it flows across the filler neck of the radiator. A few bubbles are normal, as it could be trapped air escaping your car’s cooling system. If the bubbles persist after 20 minutes of idling, though, your vehicle may have a blown head gasket.
A blown head gasket can cause bubbling in the radiator by allowing combustion gases to enter the cooling system. A healthy head gasket seals the engine block and cylinder head so that combustion gases don’t leak. If breached, however, the hot, pressurized combustion gases may enter the cooling system and cause bubbling in the radiator.
2) White exhaust smoke
Pay attention to your exhaust the next time you start your car. If you see white smoke billowing out the tailpipe, you may have a blown head gasket.
Unless your car uses diesel, it should produce clear, invisible exhaust smoke. White exhaust smoke in a gasoline-powered car engine usually indicates moisture in the combustion chamber. The only way for any substantial amount of moisture to enter this part of the engine is through a blown head gasket. Depending on where exactly the head gasket blows, it may allow coolant to enter the combustion chamber. As the engine burns air and fuel here, it will also heat the added the coolant, resulting in white exhaust smoke.
3) Loss of pressure in cooling system
Your car’s cooling system is designed to pressurize as the engine warms up. After driving for just a few minutes, the coolant will collect enough heat to expand and pressurize the cooling system. That is important because pressurized coolant has a lower boiling point than unpressurized coolant, so it doesn’t boil over and turn to steam.
A blown head gasket can cause a loss of pressure in a cooling system by breaking the otherwise closed nature of this system. If the head gasket blows between a coolant passage and a cylinder chamber, the coolant may leak into the chamber, preventing the cooling system from maintaining pressure. You can buy or rent a testing kit from most auto parts stores to see if your car’s cooling system is keeping pressure. Just remember to wait until your car’s engine has cooled off before opening the radiator.
4) Mixed oil and coolant
Another sign of a blown head gasket is oil and coolant mixing. Under no circumstances should you have oil in your coolant or coolant in your oil. Ethylene glycol — the primary chemical used to make antifreeze in coolant — isn’t an effective lubricant. If coolant enters the engine’s oil passages, it can lead to internal degradation while shortening the car’s lifespan in the process. Oil in the coolant is equally bad because oil doesn’t transfer heat as effectively as a coolant.
To see if your car’s oil and coolant are mixing, look at the oil dipstick and inside the radiator. Coolant in oil typically has a soft cream color with a foamy consistency, whereas oil in coolant manifests as black specks floating to the top of the radiator.
5) Cylinder compression loss
Compression loss in one or more cylinders is a telltale sign of a blown head gasket. The cylinders are designed to trap combustion gases so that it creates the most energy, which it uses to power the crankshaft and move the car. Depending on the specific stage of combustion, gases in the cylinder may be pressurized anywhere from 100 to 1,000 psi. In diesel engines, compression may reach up to 2,000 psi.
In some cases, a car with cylinder compression loss will perform sluggishly. In other cases, you won’t notice any change with your vehicle’s performance or handling. To see if your car is losing compression, you’ll need to test the cylinders. There are two tests used to detect compression loss in cylinders:
- Compression test: The easiest testing method, a compression test measures the amount of pressure produced by each cylinder. The tester is inserted into the spark plug port of the cylinders to determine how much pressure they produce.
- Leakdown test: A more laborious but also more accurate testing method, a leakdown test forces pressurized air — typically at 100 psi — into each cylinder via the spark plug port to see whether it holds. If you have a six-cylinder car with two cylinders that leak pressure, you may have blown head gasket between the two problematic cylinders.
Of the two testing methods, a leakdown test will provide the most accurate representation of your car’s cylinder compression.
6) Hard or rough to start
If you have trouble starting your car, or if it runs rough during startup, you may have a blown head gasket. That occurs when coolant floods one or more cylinder chambers, preventing the combination of fuel or air from igniting. The cylinder chambers must be dry for combustion to occur. Otherwise, you may struggle to start your car.
7) Engine overheating
Keep a watchful eye on your car’s engine temperature gauge when driving. While allowing your engine to overheat may cause a blown head gasket, it can also be a symptom of a blown head gasket.
A blown head gasket in which exhaust gases enter the cooling system, for example, can quickly heat the coolant. Exhaust gases are hot, so they raise the temperature of the coolant and causes the engine to overhead. Exhaust gases can also displace coolant by forcing it out the radiator and into the reservoir. And with less coolant in the cooling system, your car will overheat more quickly.
What to do if the head gasket blows
To mitigate the risk of severe engine damage, you should avoid driving your car if it has a blown head gasket. Instead, have it towed to a trustworthy mechanic who can replace the head gasket. That isn’t an easy job, nor is it cheap. While head gaskets are relatively inexpensive, it can take over 12 hours of labor to remove the old gasket and install the new one.
The mechanic will also need to check your cylinder head with a feeler gauge to determine if it’s warped. If the head isn’t completely flat, it must go to a machine shop for milling. Only then should a new head gasket be installed. If the head becomes warped, combustion gases, coolant or oil may still leak.
A blown head gasket is a common problem that sends many cars to an early grave at the local scrapyard. By replacing the gasket and checking the cylinder head for flatness, though, you can keep your car roadworthy for years to come.