Your car hasn’t been running right lately. You take it to your trusted technician and he says those words that no one wants to hear: “You have a blown head gasket.”
Your mind starts reeling as the dollar signs begin to pile up. You know it’s a labor-intensive and expensive repair but you wonder what exactly a head gasket is, what causes a head gasket to become blown and what the signs of a blown head gasket are. Read on for the answers to all your head gasket questions.
What does a head gasket do?
Your car’s engine is divided into two parts, the cylinder block where the pistons and cylinders reside and the cylinder head where the valves, spark plugs and camshaft(s) are located. Cushioned between these two massive engine parts is the head gasket.
One of the most critical gaskets in your engine, the head gasket is designed to seal the cylinders’ firing pressure and to prevent coolant and engine oil from leaking into the cylinders as well as to the outside.
The head gasket must withstand the stresses of the two surfaces expanding, shrinking, warping and rubbing while sealing in cylinder pressure, coolant and engine oil running through casting ports.
What Causes Head Gasket Failure?
Everything undergoes failure after enough time and use, but factors like these can cause head gaskets to fail sooner rather than later:
- Poor Maintenance: A lack of cooling system maintenance can lead to overheating — the most common cause of head gasket failure.
- Overheating: When your engine overheats, the cylinder head or engine block can warp or expand. When this happens, your head gasket may no longer seal properly.
- Pre-Ignition: Sometimes known as detonation, pre-ignition occurs when air and fuel ignite in the combustion chamber before it is supposed to. When this happens, combustion temperatures and pressures rise. Higher combustion temperatures and pressures can compound overheating and further test the head gasket(s).
- Installation Errors: If you’ve recently had your engine rebuilt or replaced, it’s possible that your head gasket was installed incorrectly. Don’t be too hard on the installer, though — head gasket installation can be tricky. Simply over-tightening cylinder head bolts can lead to head gasket failure!
Common Signs of a Bad Head Gasket
Want to learn how to test for a bad head gasket? If your car is suffering from this issue, it’ll probably exhibit one or more of these symptoms:
#1. Coolant Loss.
Keep an eye on your coolant levels — a significant drop is a red flag. If you’re constantly topping off your coolant but can’t find any leaks, it’s nearly always a sign that you’re burning coolant.
#2. White Smoke from the Tailpipe.
A faulty head gasket most often results in billowing clouds of sweet-smelling white smoke coming from the exhaust. Thie smoke is caused by antifreeze leaking past the gasket and into the cylinders, where it is turned to steam as part of the combustion process.
Less common, but still possible, is a leak from an oil passage to the cylinder, which would cause blueish smoke.
Either of these types of gasket failure will also allow combustion pressure into the cooling system or oil breather system.
If a radiator hose suddenly blows off its water outlet, or the dipstick won’t stay put, this could be the reason.
#3. Engine Knocking.
A bad enough head gasket leak will cause the engine to lose compression. This can lead to the engine running roughly at idle, knocking and even stalling.
However, other problems can cause the engine to run roughly or knock. To determine if your vehicle has a head gasket leak, our technicians may perform a compression leak test on your vehicle. If combustion gasses are mixing with the engine oil, that’s an indication that your head gasket may have failed internally.
#4. Milky Oil.
We know that oil and water don’t mix, but if coolant gets into the oil in your engine, the resulting mixture loses its lubricating qualities. A head gasket leak can let engine coolant mix into the engine oil system.
The resulting thick, frothy mixture can collect under the engine’s oil filler cap, so if you suspect a head gasket leak on your car, that’s a great first step: unscrew the engine oil filler cap, and look on the underside.
If a foamy, pale oil build-up has collected there, then coolant is likely contaminating the engine oil.
#5. Overheating.
An engine overheating one too many times (as a result of a clogged radiator, coolant leak, faulty fan, etc.) can cause head gasket failure but, conversely, a blown head gasket can also cause the engine to overheat.
Hot exhaust gases can leak into the cooling system, or coolant can leak into the cylinders and be burned off as steam, either way, the end result is an overheating engine.
If the car is driven while overheating, it can also result in the alloy cylinder head warping, or steam damaging the catalytic converter, adding significantly to the cost of repair.
Can You Drive a Car with a Blown Head Gasket?
If you continue to drive your car with a blown gasket then you risk damaging the engine further as the increase in heat can warp the parts connected to the gasket or cause even more problems because of leaked fluids and/or eroded parts.
Unless you want to pay a higher repair bill, or worse, have to replace the gasket or even the entire engine, then be sure to get the car inspected by a certified technician or mechanic before anything else.
How to Prevent Head Gasket Failures?
It’s much better to spend a few dollars now than several hundred dollars afterwards to cure a blown head gasket.
Yes, the replacement gasket itself isn’t expensive, but all the dismantling and reassembly is labor-intensive, which significantly increases the cost of repair, especially on modern cars.
A head gasket will often fail after repeated overheating or if you continue to drive after the car has overheated, so the best way to prevent a head gasket failure is to ensure your cooling system is in good condition.
If your vehicle does start to boil over, stop, let it cool for at least an hour, and refill the radiator before continuing.
The good news is that checking the cooling system is easy. All you need to do is check all the pipes and joins for leaks (you’ll see the dampness if there is a leak), make sure the radiator is working efficiently, the thermostat opens properly, and the coolant is topped up to the correct level.
Also make sure the fan (mechanical or electric) is working, has all of its blades, and has a shroud around it to increase the efficiency.
If you suspect a head gasket failure, the scientific test is to check for combustion gases in the cooling system. This test will show if the compression has leaked into the cooling system, and therefore if the head gasket has blown.
The old mechanic’s trick is to take off the radiator cap (only when the cooling system is cold!), start the car, and look for bubbles in the coolant.
However, these will not show if there are any other failure spots in with the head gasket, so the absence of gases in the cooling system does not guarantee a healthy head gasket.
Some older head gaskets fail because they are either a poor design, are not robust enough – or both. This used to be more of an issue with older metal gaskets, which would last only for so many years of going from cold to hot before an inevitable failure.
Thankfully modern MLS (multiple layer steel) replacement gaskets are now available for most applications, and offer improved reliability.