See full version: Causes of Diesel Engine Oil Blow By
Worn pistons cause blow by. Just as the cylinder walls wear out and the bore becomes bigger, the piston becomes worn and becomes slightly smaller. Bear in mind that aluminum is a soft metal, and grit accumulation in the combustion chamber carves grooves into the piston. These grooves are an ideal place for the compressed fuel/air mixture to escape into the crankcase. [links]
In a diesel engine, blow by is defined as the compressed fuel/air mixture in the combustion chamber leaking past the piston and entering the crankcase. Blow by is not good since it robs engine power and builds up gas pressure in the crankcase. There are reasons for blow by, and by understanding them, you can make the necessary adjustments.
All diesel engines have some degree of blow by. This is due to engineering. When metal heats up, it expands. Metals expand at different rates. When heated, aluminum expands faster than steel. Engineers have to compensate for the differences in temperature expansion. They do this by designing the aluminum piston slightly under size from the steel cylinder. If they designed the piston for a snug fit when the engine is cold, the piston would seize inside the cylinder when it heats up due to thermal expansion. An under-sized piston leads to blow by when the engine is cold. As the engine heats up, the piston expands, and blow by disappears under normal operation. This is considered typical cold engine blow by, and it is unavoidable.
As the diesel engine gets older, the cylinder walls wear out by constant piston and piston ring scraping. Over time, the cylinder bore becomes bigger by this constant scraping. The end effect is that "slop" or a gap is created between the piston and cylinder. The gap between the piston and the cylinder wall becomes significant; and as a result, compressed gases are free to go around the piston.
Researchers at the Helsinki University of Technology ran extensive studies of piston rings and concluded that worn rings are a source of blow by. What happens is the constant scraping of rings back and forth in the cylinder eventually wears them down, and their sealing capabilities fail. Blow by happens in front of the ring, but the gases also "sneak" around the backside of the ring when the sidewalls become worn.
When the timing belt is worn or damaged it can skip a tooth or several of them during rotation which desynchronizes different elements of the engine causing irregularities. It is important to fix a faulty timing belt as soon as possible because it can cause internal damage to the engine. more
Auto Repairs Are EXPENSIVE
A new battery will cost $100-$200.
The average cost of installing a new timing belt is approximately $500-$1000. The cost can vary depending on the type of vehicle you own and where you have your car serviced.
The most common descriptions of an engine misfire are a sound like a popping, sneezing, banging, chuffing, or a backfire, usually when the engine is anywhere between 1,500 – 2,500 rpm. The sound occurs when unburnt fuel exits the cylinder and is pushed out during the exhaust stroke before being ignited by the spark of the next cylinder, causing it to explode out through the exhaust system. [links]
You can also tell that you likely have an engine misfire if it sounds like your car is struggling. You may need to switch off your radio and close your windows to hear it from inside your car. If you listen closely to your engine, you will notice that it sounds different than normal. An overall change in engine sound can be an indication that one cylinder is not working. This can be confirmed by other symptoms of an engine misfire such as the vehicle lacking power under full throttle. [links]
All of the input and output engine management devices (i.e., sensors, ignition coil packs, etc.) are connected where needed via electrical circuits. Problems within these circuits, such as damaged wiring or a loose connection, can cause an engine misfire.
A misfire can be caused by a myriad of issues. However continuing to run an engine that is misfiring can cause catastrophic damage – and the longer you put off fixing the cause of the misfire, the more damage you’ll cause to the engine. In the worst-case scenario, a continuing misfire could cause some costly problems that could effectively destroy your engine. [links]
As you’re driving a misfire can cause the engine to lose power infrequently, or a brief hesitation in acceleration when the throttle is pressed. Acceleration may be rough or the car feels like it’s lost power and accelerates slower than usual. The engine may feel like it’s stumbling for a few seconds before regaining pace. This can be caused by an incorrect air/fuel mixture due to a faulty O2 sensor. Alternately, a misfiring cylinder can unbalance the engine, causing a shaking sensation. [links]
To keep the crankcase from becoming pressurized, causing issues with oil sealing and robbing the engine of power, blow-by is pulled from the crankcase via the positive crankcase ventilation (PCV) system and routed back into the intake. 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.
Let’s start at the top. It makes sense that a catch can would still have to allow blow-by gasses to be vented from the crankcase; after all, that’s the entire purpose of the PCV system. However, how that is done is a controversial topic. Some catch cans simply have one line coming from the crankcase to the can and then use a small breather filter to allow pressure to vent out of the top of the can. This method completely eliminates the possibility of blow-by being recirculated into the intake.
Another issue with simply venting the catch can to atmosphere is the fact that most modern crankcase ventilation systems are under vacuum from the intake manifold. This vacuum helps clear oil and, more importantly fuel vapors, from the crankcase faster. The longer these vapors stay in the crankcase, the more likely they will condense, causing damage to internal engine components and thinning the oil. The vacuum also allows leftover combustion gasses to be recirculated and burned again, making for a more environmentally friendly vehicle and less sad dolphins. Therefore, if the factory PCV system is routed to the manifold vacuum, your catch can should be too.