Home Car Tips 7 Signs of a Blown Head Gasket

7 Signs of a Blown Head Gasket

by Frank
blown head gasket

Hearing from the mechanic that your car has a blown head gasket is a driver’s worst nightmare. Based on the type of car, it may cost more than $1,000 to replace a blown head gasket. Before spending that kind of cash, drivers should perform their own diagnosis to determine if they truly have a blown head gasket.

Read Next: What to Do When Your Car Overheats

What is a Head Gasket?

Let’s begin by talking about what a head gasket is. The head gasket resides between your engine block and cylinder head. Every modern automobile has this gasket but they vary in their depth and structure based on the company’s design of the motor.

The head gasket is so important as it seals the combustion chamber allowing your car to have the correct compression and contains exhaust gases both of which assist in maintaining the efficiency of your engine. The head gasket also keeps coolant and oil from the combustion chamber that’s important for the exact reasons you would not want coolant or oil leaking anywhere else.

Now that we know what a head gasket it, it is important to learn what blown head gasket symptoms look like and to avoid higher costs as a result of additional engine damage resulting from driving with a blown head gasket. To understand the symptoms it can be useful to know why a head gasket could fail.

Why Do Head Gaskets Fail?

The head gasket forms a seal between the engine block and the cylinder head. This means that your head gasket must seal both exceptionally hot, high-pressure combustion gases in addition to engine coolant which may be anywhere from cold ambient temperatures to the typical working temperature of your engine. Due to the wide variety of temperatures and relatively large surface area, it’s not uncommon for head gaskets to develop leaks over time. This can happen whatever the make or model of your vehicle or the sort of head gasket used.

Considering that the head gasket seals the coolant passage both from the air and the combustion chamber you can not see much of the head gasket on a car with the engine installed. Because a lot of the gasket cannot be viewed without disassembling the motor, blown head gaskets symptoms can be quite tricky to diagnose. Since a visual inspection usually won’t establish a head gasket leak, it’s crucial that you be aware of the other symptoms so that you may correctly diagnose a head gasket issue.

See also: How to Keep an Old Car Running Forever

7 Signs Your Car Has a Blown Head Gasket

The head gasket, located between the engine block and cylinder head, is a vital part in modern automotive engines, designed to reduce combustion gases and prevent oil, and coolant from leaking. The head gasket keeps these fluids in their various passages, allowing for optimum engine performance.

Head gaskets can be prone to failure or “blow” when the motor overheats or from regular use. If you think your car has a blown head gasket, you should check these seven signs of possible head gasket failure:

Bubbles in radiator

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 vehicle’s engine to completely cool off — usually about two hours after driving — and carefully remove the radiator cap with a towel or rag. Now crank your vehicle and watch the coolant as it flows across the filler neck of the radiator. A few bubbles are normal, as it could be trapped air penetrating your car’s cooling system. If the bubbles persist following 20 minutes of idling, though, your vehicle may have a blown head gasket.

A blown head gasket can cause bubbling from the radiator by allowing combustion gases to enter the cooling system. A head gasket seals the engine block and cylinder head so that combustion gases do not leak. If breached, however, the hot, pressurized combustion gases can enter the cooling system and cause bubbling from the radiator.

Besides allowing coolant into the combustion chamber, an internal head gasket leak allows exhaust gases to enter the coolant. This may cause bubbles in the radiator or coolant reservoir which makes the coolant seem like it is boiling even when it is not warm.

The bubbles are exhaust gases which force their way into the cooling system through the combustion process. An easy do-it-yourself evaluation for a blown head gasket would be to perform a chemical test to check for the existence of exhaust gases to find out if this is occurring in your vehicle. This is the most successful blown head gasket test and can give you a positive indication of a blown head gasket.

White exhaust smoke

white exhaust smoke

Look closely at your exhaust the next time you start your vehicle. If you see white smoke billowing out the tailpipe, you might have a blown head gasket.

Unless your vehicle uses diesel, it must create clear, invisible exhaust smoke. White exhaust smoke in a gasoline-powered automobile engine generally indicates moisture in the combustion chamber. The only way for any significant quantity of moisture to get into this portion of the engine is by way of a blown head gasket. Based on where precisely the head gasket blows, it might allow coolant to enter the combustion chamber. As the motor burns air and gas here, it will also heat the additional coolant, leading to white exhaust smoke.

Most head gasket leaks are internal to the motor allowing coolant to flow in the combustion chamber on every intake stroke. When this occurs to coolant it burns/evaporates with the combustion process and appears as white smoke coming from the tailpipe. This smoke can be discerned from moisture through a cold start by a sweet odor and will last even when the engine is warm. If the flow in the head gasket is big this white smoke may frequently be excessive and billow in the tailpipe.

Loss of pressure in the cooling system

cooling system pressure test

Your vehicle’s cooling system is designed to pressurize as the engine warms up. After driving for only a couple of minutes, the coolant will accumulate enough heat to enlarge and pressurize the cooling system. That is crucial since pressurized coolant has a lower boiling point than unpressurized coolant, so it will not boil and turn to steam.

A blown head gasket can result in a loss of pressure in a cooling system by dividing the otherwise closed character of the system. If the head gasket blows between a coolant passage and a cylinder chamber, the coolant may flow into the cylinder, preventing the cooling system from maintaining pressure.

You can purchase or rent a testing kit from most auto parts stores to find out if your vehicle’s cooling system is maintaining pressure. Just make sure you wait until your vehicle’s engine has cooled off before opening the radiator.

Mixed oil and coolant

oil in coolant

Another indication 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 main chemical used to make antifreeze in coolant –is not an effective lubricant. If coolant enters the engine’s oil passages, it may result in internal degradation and shorten the car’s lifespan in the procedure. Oil in the coolant is every bit as bad because oil does not transfer heat as efficiently as the coolant.

As coolant leaks into your combustion chamber, it will seep past your piston rings into your oil.  Over time oil and water will mix and cause the oil to turn a milky white.  You can look for this on your dipstick and around your engine oil cap.  Having water in your oil will make your oil ineffective in properly lubricating your motor which will quickly allow wear on your cylinder walls and on the crank and camshaft bearings.  Even if you don’t drive the vehicle, the presence of water in the oil can cause rust on machined surfaces which can lead to pitting in the metal and necessitate an engine rebuild.

To see if your vehicle’s oil and coolant are mixing, then examine the oil dipstick and within 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 surface of the radiator.

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Cylinder compression loss

engine compression test

Compression loss in one or more cylinders is a telltale indication of a blown head gasket. The cylinders are made to trap combustion gases so that it generates the energy, which it uses to power the crankshaft and move the vehicle. Based on the particular period of combustion, gases in the cylinder might be pressurized everywhere from 100 to 1000 psi. In diesel engines, compression may reach up to 2000 psi.

Sometimes, a vehicle with cylinder compression reduction will perform sluggishly. In other instances, you won’t notice any change with your vehicle’s performance or handling. To see if your vehicle is losing compression, you will need to check the cylinders. There are two tests used to detect compression loss in cylinders:

  • Compression test: The simplest testing method, a compression test measures the amount of pressure generated by each cylinder. The tester is put into the spark plug port of the cylinders to ascertain how much pressure they create.
  • Leak down test: A more laborious but also more accurate testing method, a leak down test forces pressurized air –normally 100 psi — into each cylinder through the spark plug port to find out whether it holds.

Of the two testing methods, a leak-down test will provide the most accurate representation of your car’s cylinder compression.

Engine Problems

engine problems

If you have trouble starting your car, or even if it runs roughly during startup, you might have a blown head gasket. This happens when cooling begins flooding one or more cylinder chambers, preventing the mix of fuel or air from igniting. The cylinder chambers have to be dry for combustion to occur. Otherwise, you might struggle to start your vehicle.

As coolant burns in your combustion chamber, it is going to leave tiny white deposits on your spark plug typically round the ground strap and electrode. Other issues can cause these white deposits so this is not a conclusive blown head gasket symptom but when others exist it could provide you more proof.

If your vehicle’s engine has been slow or unresponsive, you could be dealing with a blown gasket. Your motor will experience a reduction of compression if your head gasket incurs any damage, possibly causing it to overheat. If your car or truck exhibits these symptoms, make certain to address the issue immediately, as an overheated motor can pose major safety hazards.

Related: How to Check Engine Fluids

Engine overheating

engine overheat

Keep a watchful eye on your car’s engine temperature gauge when driving. While allowing your engine to overheat can cause a blown head gasket, it can also be a symptom of a blown head gasket.

A blown head gasket where exhaust gases enter the cooling system, as an example, can quickly heat the coolant. Exhaust gases are hot, so that they increase the temperature of the coolant and causes the engine to overheat. Exhaust gases can also displace coolant by forcing it out the radiator and to 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.

Can you drive with a blown head gasket?

For those who have multiple blown head gasket symptoms, it’s very important to drive your vehicle as little as possible. The hot gases and cold coolant moving through the hole in the gasket can easily erode or twist the metal head or engine block leaving you with expensive machining invoices or even having to buy new heads or a brand new engine and having water in your engine oil may ruin bearings quickly.

Can a blown head gasket be avoided?

There are some ways you can reduce your chances of blowing a head gasket.  The first is to keep combustion chamber pressures as low as possible.  If your vehicle is turbocharged or supercharged, make sure your boost level is set to the factory setting to keep combustion pressures in check.  Also, make sure your engine doesn’t have any preignition or knocking from overly advanced timing or carbon build up.  Similarly, maintaining low engine RPMs will reduce stress and heat on your head gasket so avoid running your engine at high RPM.  Lastly, if your car has a manual transmission avoid downshifting to slow the car and rev-match anytime you can to reduce pressure on your head gasket.

If you are rebuilding an engine, you can reduce the probability of a blown head gasket in the long run by using properly lubricated head studs torqued in the appropriate sequence to the correct torque setting. You can also make sure your block deck and cylinder head mating surface are appropriately prepared for the new gasket. Similarly, using a multi-layer steel or other metal head gasket can enhance the reliability of your motor. For more information, check our article on how to avoid a blown head gasket

How much does it cost to fix a blown head gasket?

Head gasket repair cost may vary significantly from vehicle to vehicle. Cost factors include:

  • Number of cylinder banks
  • Overhead cam VS pushrod engines
  • Head or block damage
  • other components replaced

The majority of the expense of a head gasket repair is in the labor costs so the complexity of the job can change the price significantly. For example, a “V” style engine has two heads and it’s best to replace the gasket on both so the cost increases significantly over an inline engine. Similarly, an engine with overhead cams adds the complexity of removing the timing belt or chain which makes the job more complicated than it would be on a pushrod engine where you simply must remove the rockers and pushrods.

Machine work can add plenty of price to a head gasket job so knowing how much damage has been done to your block or head is important in calculating the cost of your head gasket repair. Lastly, there are lots of other parts which can be replaced when repairing a head gasket as with other gaskets and seals, belts, or the water pump and those parts costs can add up quickly as well. To find out more on calculating the head gasket repair prices for your car, check out our post on head gasket repair prices.

Do not risk getting stranded or damaging your car’s engine by driving with a blown head gasket.


A blown head gasket is a frequent problem that sends many automobiles to an early grave at the local scrapyard. By replacing the gasket and assessing the cylinder head for flatness, however, you may keep your vehicle roadworthy for many years to come.

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