Years ago I owned a VW diesel. Although the combustion is different than gasoline engines, they are both basically the same engines structure wise. Below is what I got off of a website that comments on both diesel and gas combustion engines.
Accumulation of Lube Oil
Another trouble that may prevent you from stopping an engine is accumulation of lube oil in the intake air passages-manifold or air box. Such an accumulation creates an extremely dangerous condition. You can detect excess oil by removing the inspection plates on the covers and examining the air box and manifold. If you discover oil, remove it and perform the necessary corrective maintenance. If oil is drawn suddenly in large quantities from the manifold or air box into the cylinder of the engine and burns, the engine may run away. The engine governor has no control over the sudden increase in speed.
An air box or air manifold explosion is also a possibility if excess oil is allowed to accumulate. Some engine manufacturers have provided safety devices to reduce the hazards of such explosions.
Excess oil in the air box or manifold of an engine also increases the tendency of carbon to form on liner ports, cylinder valves, and other parts of the combustion chamber.
The causes of excessive lube oil accumulation in the air box or manifold will vary depending on the specific engine. Generally, the accumulation is due to an obstruction in either the air box or separator drains. In an effort to reduce the possibility of crankcase explosions and runaways, some engine manufacturers have designed a means to ventilate the crankcase. In some engines, a passage between the crankcase and the intake side of the blower provides ventilation. In other engines, an oil separator or air maze in the passage between the crankcase and blower intake provides ventilation.
In either type of installation, stopped up drains will cause an excessive accumulation of oil. Drain passages must be kept open by proper cleaning whenever necessary.
Oil may enter the air box or manifold from sources other than crankcase vapors. A defective blower oil seal, a carryover from an oil-type air cleaner, or defective oil piping may be the source of trouble.
Another possible source may be an excessively high oil level in the crankcase. Under this condition, an oil fog is created in some engines by the moving parts. An oil fog may also be caused by excessive clearance in the connecting rod and main journal bearings. In some types of crankcase ventilating systems, the oil fog will be drawn into the blower. When this occurs, an abnormal amount of oil may accumulate in the air box. Removal of the oil will not remove the trouble. The cause of the accumulation must be determined and the necessary repair made.
If a blower oil seal is defective, replacement is the only satisfactory method of correction. When you install new seals, be sure the shafts are not scored and the bearings are in satisfactory condition. Take special precautions during the installation to avoid damaging the oil seals. Damage to an oil seal during installation is usually not discovered until the blower has been reinstalled and the engine has been put into operation. Be sure an oil seal gets the necessary lubrication. The oil not only lubricates the seal, reducing friction, but also carries away any heat that is generated. For most purposes, soak new oil seals in clean, light lube oil before you install them.
