Why do pistons blow

We passed a car on Highway the other day with the hood up and steam or smoke billowing out. My husband said the engine had probably blown up and that would be expensive. What would cause an engine to "blow up? There are many types and causes of engine failure.

The most catastrophic — and visual — is a broken connecting rod punching a hole in the block or crankcase.

A connecting rod is the part that connects a piston, which is moving up and down very quickly, to the rotating crankshaft. If the rod is broken, the crank keeps turning and can push the broken rod right through the side of the cast iron or aluminum block or the crankcase, which holds the oil. In either case, the engine will stop immediately and the hot oil escape through the hole in block or crankcase and onto the hot exhaust causing a lot of blue smoke or even a fire.

Another form of engine failure is a broken valve punching a hole through the top of a piston. In this case, the pressurized oil will escape through the top of that piston out through an exhaust valve.

Other common issues seen are poor cylinder finish and excessive clearances in the ring land. The bore diameter establishes the tension of the ring because it either compresses it in or it releases it out. Cylinder bore straightness, roundness and surface finish with a correct hone pattern, are key to the success of any piston ring. According to Keiffer, the cylinders can contribute to blow-by if you have poor cylinder finish, poor geometry or they are oversized, resulting in poor ring fit and excessive end gaps on compression rings.

As far as rings are concerned, you want to make sure you use a quality ring that is truly flat and parallel on the piston, meaning there are no parts of the ring not touching the cylinder bore to eliminate leakage paths.

The next thing is controlling the end gap. In this article: crosshatch , Cylinders , dynamometers , Piston Rings. Watch Engine Builder's latest discussions and explanations. Shop the latest Engine Builder merchandise. Stay up to date by signing up for the Engine Builder newsletter. By Justin Anning. By Derek Cho-Sam. By Stefan Rossi. Features: Vote for the Diesel of the Year.

Features: Vote for the Engine of the Year. Video Series View More Videos. Podcasts Listen To More Podcasts. Buyer's Guide Supplier Spotlight. PennGrade Motor Oil. Contact: Bobbi Brophy Phone: Phone: Learn More. The pistons do not actually touch the cylinder walls, but ride on a level of oil that lubricates the cylinder walls. The continuous movement of the pistons over time can lead to damaged cylinder walls, due to the friction and consistent movement. In a diesel engine, you will see that the gap in the cylinder caused by the continuous piston usage leads to the compressed glasses being passed easily into the piston.

In order to avoid your engine or diesel engine prevent blow-by, there are some steps you could take to keep a healthy and functioning system. If you let the buildup occur within your engine, this can erode metal and cause the breakdown of parts. Adding treatments to the fuel and oil will aid in the dissolving of solids and prevent the buildup in liquid form. In addition, try using only high quality oils and fuels to keep the engine running smoother for longer, and prevent any possibilities of engine combustion.

The use of high quality oils will prevent creating solid byproducts which can wear away on the metal over time. Lastly, collect and send oil samples to be tested for any foreign particles and debris that can degrade your system over time. So now the main question is, how do you fix a blow-by? This is the most important question, since a blow-by will significantly reduce engine efficiency.

By increasing the intake of oil and fuel the piston rings and cylinder walls will wear down, causing more fuel to make its way into the crankcase. Blow-by can also damage the intake valves, creating an optimal system that needs immediate fixing.

Blow-by is typically caused by compression going through the pistons, through the crankcase, and reducing the efficiency of the system along the way.

In most cases, the engine will have to be taken apart in order to find a solutinto the problem. This is a time-consuming and costly procedure. However, if your vehicle is a bit older, there are some other things you can try first to get your vehicle to run for a little bit longer before you search out a permanent fix.

If your car is experiencing blow-by, sometimes you immediately think you should buy a new engine. You can do some regular maintenance, along with cleaning the engine, to prevent buying a new part that will cost thousands.

If the rest of the components of the engine are performing the way they should, you can use a flushing oil concentrate to clean the engine. The concentrate is designed to remove sludge, reduce smoke, and reduce blow-by, which in turn, helps the piston rings and compression. Flushing oil concentrate is possibly the fastest and most efficient way to clean the sludge from your engine.

You may be seeing the problem already; oil and fuel are not what you want in your air intake system. Many modern cars employ some sort of air-oil separator system to minimize the amount of oil and fuel vapors that reach the intake.

Due to cost and maintenance restrictions, however, these stock systems are usually not completely effective. Over time, blow-by can reduce engine efficiency as it coats parts of the intake in oil and fuel. In forced-induction and intercooled engines, blow-by often coats the inside of the intercooler, severely affecting its ability to transfer heat and cool the intake charge.

These issues become even more apparent with age. As piston rings and cylinder walls wear, more and more fuel and oil is able to pass into the crankcase and eventually into the intake system. The effects of blow-by are not always limited to just the intake and charged air cooling systems; in some cases, the intake valves and other engine internals can suffer as well.

This allows more blow-by into the crankcase, and because the engine is still cool and then shut down, that blow-by condenses in large amounts inside the crankcase and PCV system. Eventually that condensed blow-by makes its way into the head and cylinders.

Blow-by that makes it into the cylinder can lower the effective octane rating of the air-fuel mixture. If the octane rating of the air-fuel mixture drops enough, it can cause knock also known as pre-ignition , where the fuel mixture ignites before the spark plug fires, causing very high cylinder pressures. Knock is one of the biggest killers of engines and can ruin even the strongest of builds. The oil and fuel vapors can also coat spark plugs, fouling them in short order and causing misfires.

To compound the problem, in short-run situations, the valves never heat up enough to burn off carbon, so any blow-by that does make it to the valves will accumulate as sludge and carbon buildup. Carbon accumulation on valves is a huge issue for gas direct-injected GDI engines. In a GDI engine, fuel is injected into the combustion chamber downstream of the intake valves, eliminating the cleaning effect of fuel washing over the intake valves.

This means that blow-by can build up on the backs of the valves even faster, impeding airflow and causing potential running issues. I think you get the point. Blow-by is a giant menace that only wants to rob your engine of power and slowly destroy it.

So what can you do about it?