Symptoms of a Bad Piston

Most car engines today have a certain number of cylinders. Four-cylinder and six-cylinder engines are most common, but there are quite a few eight-cylinder engines on the road as well. Some exotic and high-end luxury cars can have ten-cylinder, twelve-cylinder, and even sixteen-cylinder engines.

For each cylinder that is found in a particular car’s engine, there is a piston located within it. The piston is a cylindrical piece of metal that moves up and down inside each cylinder, compressing the air-fuel mixture and capturing the force created by the combustion process. This force is then transferred to the crankshaft, via the connecting rod. The power that is produced by all of the engine’s pistons, firing in a preset sequence, is transferred to the car’s transmission and then to the wheels, propelling the car down the road.

Most contemporary pistons are made of cast aluminum alloy. For the best possible sealing of the piston within each cylinder, a series of spring-loaded rings are inset into grooves around the circumference of the piston. Some of these piston rings prevent the combustion forces from escaping around the edges of the piston, while others are there to scrape the lubricating oil off of the cylinder walls, so that the oil will not be burned along with the fuel.

Signs of a bad piston

A bad piston is usually the consequence of some other type of engine problem, and not the cause. Pistons do not generally malfunction on their own, but tend to fail as a result of lack of proper maintenance, or the failure of another component. There are several symptoms of a bad piston. Let’s see what they are:

• Piston noise: If your pistons are worn, there can be too much clearance between the piston and the cylinder wall. This can cause a noise known as “piston slap,” which can be a sign of a bad piston, especially if you hear it after your engine has fully warmed up.

• Blue smoke from the exhaust: If you have a bad piston, the oil from the crankcase could be getting past the piston and into the combustion chamber, where it mixes with the fuel and is burned. The blue color of your exhaust likely indicates that you are burning oil. You may also notice increased oil consumption when you check your oil.

• Reduced engine power and poor performance: A bad piston can keep your engine from producing all the power it was designed to. In severe cases, your piston can be cracked or even have a hole in it. This greatly reduces the engine’s compression, cutting the power output.

• Your check engine light comes on: A bad piston can definitely throw off your car’s emissions. This will often cause your engine computer to trigger the check engine light on your dashboard. Trouble codes in the computer may indicate that the source of the problem is in a specific cylinder.

Should you drive your car with a bad piston?

Please don’t. If your car has a bad piston, there has already been serious engine damage. Why make it worse by continuing to drive it? It is possible that the bad piston can be fixed before the problem gets any more severe. Call an experience mechanic right away and have your car towed right to the repair shop.

How do you fix a bad piston?

The key issue with fixing a bad piston is this: How much additional damage has been done to the engine? A bad piston can easily cause damage to the cylinder it is located in, as well as other engine parts, such as the valves and connecting rods, located both above and below it.

There are some preliminary tests that can be done to determine the extent of the damage from a bad piston, before it becomes necessary to take the engine apart:

• A compression test will check how well the piston is sealing the combustion chamber area
• A leakdown test will check if compression is escaping downward into the crankcase area
• A bore scope, inserted through each spark plug hole, will give visual evidence of any physical damage to the pistons, including holes and cracks
• An analysis of any trouble codes in the engine computer can identify the location and possibly the cause of the bad piston

Once the bad piston or pistons have been identified, the next step is to take the engine apart, to the extent necessary to assess the damage. A bad piston can have been damaged in a variety of ways, including:

• Burned piston: The top of the piston has a hole burned through its top, or it may look melted. It is usually caused by excessive heat in the cylinder.
• Cracked piston: The piston has cracks, going partially or completely through it. It is usually caused by the force of detonation, a result of the fuel-air mixture in the cylinder igniting at the wrong time.
• Scored piston: The piston has vertical scratch marks down its sides, and sometimes pockmarks or dents on its top. It is usually caused by debris getting into the cylinder, often from poor air filtration or inadequate crankcase ventilation.
• Scuffed piston: The piston has scraped itself against the cylinder wall. It is usually caused by poor lubrication, overheating, or some other source of excessive heat.
• Shattered piston: The piston has been destroyed because it has collided with the intake or exhaust valves at the top of the cylinder. This can happen because many of today’s engines are known as “interference engines.” This means that if the timing chain or belt that controls the valves slips out of alignment, the pistons can actually hit the valves, causing damage to both components. This is very serious, extensive, and expensive damage.

Now that the damage has been fully exposed, an estimate of repair costs can be produced. The work required to repair the damage from a bad piston can range from a mild engine rebuild to a total engine replacement. Once this is known, you will have a decision to make.

Is it worth repairing the damage from a bad piston?

Assuming that your car is not covered under warranty (in which case you will not pay for repairs), here are some broad guidelines as to what to do about a bad piston, in consultation with your mechanic:

Have your car repaired if: - Your car is fairly new and repairs are not too expensive - Your car is valuable and the repair cost is acceptable in light of that - Your car has sentimental value, you want to keep it, and you can afford to fix it

Do not have your car repaired if: - Your car is old, has a lot of miles on it, and is not worth much - Your car is unreliable, costs a lot to keep running, and repairing a bad piston won’t change that - The cost of repairs is close to or more than your car’s value

If you decide not to have your car repaired, it is time to bid it farewell.

Can you replace a bad piston by yourself?

Unless you are an experienced engine rebuilder, the answer is no. Bad pistons can mean that there is extensive engine damage that will require sophisticated skills and specialized tools to repair. It’s not your typical DIY job.

You can prevent a bad piston

Preventing piston problems is a much easier and less expensive course of action than having to pay for an expensive repair (or junking your car) after it happens.

The trifecta of not changing the oil, not maintaining the coolant, and not replacing your spark plugs will put you in the loser’s circle when your engine destroys its pistons, along with many more of its moving parts. You have been warned; don’t let this happen to you!