Josh;
The camshaft driven lift pump is sort of a Yanmar thing. Most Cummins, Perkins, Beta, Universal, Mitsubishi, etc. engines built in the last 15-20 years (and the newer high pressure common rail Yanmars) use an electric lift pump. Just like your fuel injected car engine, it is necessary to pressurize the HP injection pump prestart to ensure the reservoir in the pump is full to get proper injector volume. If the seals in the high pressure pump are leaking, you can get fuel into the engine oil. But you’ll notice hard starting, increased vibration, and rough engine operation long before you see much fuel in the oil pan. The most likely source of fuel in the oil is a combination of worn rings and faulty injectors. The later can cause the former, BTW. Excess fuel injected can remove the film of oil that seals the rings and “wash out” the cylinder walls causing loss of compression and wear of the rings and cylinder wall. The excess, unburned, fuel gets into the oil. The resulting fuel/oil mix being splashed or forced into the cylinder by excessive pressure in the oil pan is the likely cause of a runaway engine. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Josh Muckley via CnC-List Sent: Tuesday, July 31, 2018 8:09 PM To: C&C List <cnc-list@cnc-list.com> Cc: Josh Muckley <muckl...@gmail.com> Subject: Re: Stus-List Oil pressure and smoke To build on Neil's thoughts: diesels typically have an approved lube oil consumption rate - they burn it. So over time the level should go down... Slowly. The GM, QM, and HM series engines (at least) have 2 fatal flaws in the fuel system. -The first and most likely is the lift pump. It is a diaphragm pump the has a drive lever the sticks in the side of the engine block. If the diagram develops a leak then fuel can leak into the oil sump. -The second is the HP fuel pump. Clearances can wear in the pump and leak fuel into the sump. You'll see the sump level increase in both cases and you might smell fuel in the oil. If you put a drop of oil on a paper towel you can observe a halo of fuel develop. The fuel thins the oil potentially damaging the bearings and cylinders. Neglected long enough and accumulating high enough concentrations it might cause a fire or a runaway diesel. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD
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