An internal combustion engine includes a first blow-by gas passage defined in a second wall. The internal combustion engine includes a second blow-by gas passage defined in a third wall. The internal combustion engine includes a third blow-by gas passage defined in a fourth wall. The first blow-by gas passage to the third blow-by gas passage connect an oil chamber and an oil separator to each other. The second wall includes a first connecting path. The fourth wall includes a second connecting path. The first connecting path connects the first crank chamber and the second crank chamber. The second connecting path connects the third crank chamber and the fourth crank chamber to each other. The third wall does not have a passage connecting the second crank chamber and the third crank chamber to each other.

An internal combustion engine, having a cylinder crankcase delimiting a crank chamber and a lubricant pan accommodating a lubricant sump, which has a lubricant pan upper part arranged between the crank chamber and the lubricant sump and a lubricant pan lower part fastened on the lubricant pan upper part. Multiple ridges originate from a base component of the lubricant pan upper part in the direction of the lubricant sump, which ridges partially intersect and thus form chambers which are peripherally closed in section between them, and lubricant passage openings formed in the lubricant pan upper part open into at least part of the chambers, via which openings the crank chamber and the lubricant sump are fluidically connected.

An outboard motor to be attached to a hull of a marine vessel that reduces an amount of oil in blow-by gas reaching a breather chamber includes an internal combustion engine including a cylinder block including at least one cylinder. The cylinder block includes two blow-by gas flow paths to guide blow-by gas from a crank chamber to a breather chamber, and the internal combustion engine is oriented such that a crankshaft extends along a direction perpendicular or substantially perpendicular to a bottom of the hull when the marine vessel is sailing.

During a predetermined operation state in which the opening degree of a throttle valve is fixed, an air flow meter positioned more on the upstream side than a pressure control valve detects a first intake air amount when the opening degree of the pressure control valve positioned on the upstream side of the throttle valve is set to a predetermined first valve opening degree and a second intake air amount when the opening degree of the pressure control valve is set to a predetermined second valve opening degree smaller than the first valve opening degree. On the basis of the first intake air amount and the second intake air amount, a diagnosis is made regarding whether there is an abnormality in a first pipe, a second pipe, a third pipe and the like which are included in a blow-by gas recirculation system for blow-by gas treatment.

Engine includes: crankcase housing crankshaft extending in vertical direction; cylinder block mounted on side of crankcase and formed with cylinder; cylinder head mounted on side of cylinder block and provided with air inlet port and air outlet port communicating with cylinder; cylinder head cover mounted on side of cylinder head and covering air inlet port and air outlet port; mount case including: supporting portion provided below crankcase and cylinder block and supporting crankcase and cylinder block; and extending portion extending from supporting portion below cylinder head and cylinder head cover; oil pan provided below mount case and storing lubricating oil; and communication tube communicating first space formed between cylinder head and cylinder head cover and second space formed between mount case and oil pan. Communication tube is provided between cylinder head cover and extending portion.

The ventilator-equipped engine is configured to: guide a blow-by gas generated in a crankcase to an intake passage through an inside of a cylinder head, an inside of a head cover, and a pressure regulating valve; and to directly introduce fresh air into an internal space of the cylinder head by providing a fresh air introduction passage that extends across the intake passage and the cylinder head.

A breather device and a snow removal machine having the breather device have a casing into which blowby gas of an engine flows, an air suction port for letting out gas from the inside of the casing, and a gas-liquid separation mechanism for separating moisture contained in the blowby gas. The gas-liquid separation mechanism separates an inlet, which allows the blowby gas to flow in, and the air suction port by a predetermined distance, and has the air suction port positioned above a liquid path through which the moisture flows. A gas path allows the blowby gas to flow from the inlet to the air suction port without passing through an air cleaner element.

This blow-by gas system is provided with: a blow-by gas flow path through which a blow-by gas discharged from an internal combustion engine passes; and an oil separator disposed midway along the blow-by gas flow path. A downstream end of the blow-by gas flow path connects to at least one of a predetermined portion of an intake passageway and a midway portion of an air introduction passageway. The predetermined portion is a portion at which at least some of the blow-by gas that has flowed into the intake passageway flows into the air introduction passageway together with an intake air in the intake passageway.

An internal combustion engine includes a forced-induction device, a blow-by gas passage, and a PCV pressure sensor detecting a pressure in the blow-by gas passage as a PCV pressure. A period during which an intake fluctuation amount, which is a fluctuation amount of an intake air amount per unit time, is greater than or equal to a specified value is defined as a specific period. The diagnosing apparatus executes a process of calculating a pressure fluctuation amount, which is a fluctuation amount of the PCV pressure in the specific period, a process of correcting the pressure fluctuation amount to a smaller value when the intake air fluctuation amount in the specific period is relatively large than when the intake air fluctuation amount is relatively small, and a process of determining, based on the corrected pressure fluctuation amount, whether there is an anomaly in the blow-by gas passage.

The ventilator-equipped engine is configured to: guide a blow-by gas generated in a crankcase to an intake passage through an inside of a cylinder head, an inside of a head cover, and a pressure regulating valve; and to directly introduce fresh air into an internal space of the cylinder head by providing a fresh air introduction passage that extends across the intake passage and the cylinder head.