The potential hazards to avoid when buying a used car is long. But a blown head gasket is near the top of the list.
The head gasket is vital to the engine’s proper operation. Sandwiched between the engine block and the cylinder head, the head gasket seals the two together. When working properly it not only ensures the combustion chamber stays air-tight, but also keeps coolant and oil out of the cylinders where, if left unaddressed, they can cause all sorts of problems, from misfires to overheating and eventually catastrophic engine failure.
Changing a head gasket is a big job, even for an experienced DIYer. It requires the complete disassembly of the engine’s top end, including the removal of the cylinder head. A new head gasket only costs about $30-$100, but the installation can take as much as 20 hours on some vehicles. It might be worth your time since paying a mechanic to do the work can cost thousands of dollars.
Fortunately, it's pretty easy to detect a blown head gasket if you know what to look for. In this guide, we'll cover the tell-tale signs.
Sweet-Smelling White Exhaust Smoke
One of the most noticeable signs of a blown head gasket can be seen – and smelled – from the exhaust. When a head gasket fails, it can allow coolant into the combustion chamber. Then, as the engine runs, the wayward coolant vaporizes, exiting the tailpipe in a thick white cloud with a sweet odor.
You'll typically see this when you start the engine or when under heavy acceleration. Unlike the whisps of water vapor that you might also see on a cold day, this vapor lingers in the air and has a tinge of sweetness, which comes from the ethylene glycol found in the coolant.
Vaporized coolant can also steam-clean the spark plugs, leaving them looking out-of-the-box new. Pulling and inspecting the engine’s spark plugs can be a surefire way to diagnose numerous engine issues including a blown head gasket.
Coolant Mixed with Oil: The Dreaded Chocolate Milkshake
The next thing to look for is coolant mixed with the engine oil, which is also easy to spot. Just open the oil cap or pull the dipstick. You want to see translucent oil that is amber to dark brown in color. This indicates a healthy engine. If you see a frothy, milky substance resembling a chocolate milkshake, it's a clear sign the car has a blown head gasket.
In such cases, the failure has allowed coolant to seep into the oil passages, mixing the two. This is bad news because coolant-contaminated oil quickly loses its ability to lubricate critical internal components. Over time, this leads to increased friction, overheating and eventually catastrophic damage. Moreover, it can cause internal parts to corrode, further accelerating their deterioration.
Bubbles in the Cooling System
Another unmistakable trouble sign is bubbles in the radiator or coolant reservoir. This means the head gasket has failed near the combustion chamber, allowing hot fumes from ignition to force their way past the breach and into the cooling system.
To check for this, start the engine and let it reach its normal operating temperature. Open the hood and carefully observe the coolant reservoir and the radiator cap. If you see any bubbling or hear any gurgling in those areas, air is likely entering the cooling system where it shouldn't be.
External Coolant or Oil Leaks
While the first three signs point to internal breaches, the head gasket can also fail externally, causing visible seepage of oil or coolant (or both) where the engine block meets the cylinder head. Just look for areas of wetness or residue along that mid-engine seam.
To get a clear view you may need to remove some components or examine things from below. A flashlight and mirror may come in handy. Don't forget to check underneath the car for additional evidence in the form of drips or puddles.
Small external leaks aren't cause for immediate alarm. However, over time, they can result in a drop in fluid levels, which will eventually lead to overheating and engine damage if left unchecked. Worse, they may signal that the head gasket is compromised on the inside, too, where the resulting problems are more serious.
Armed with these tips you can identify a blown head gasket before you purchase a used car, saving you from a complicated repair and a host of related issues, such as overheating and premature engine wear.
Still have questions? Speak to one of our Tinker Experts today
