so, in the two stroke engine, the fuel and air passes through the crank case, and it's said you can't have an oil sump in there because it would get consumed into the engine.

However, I know like my prius engine for example, actually doesn't have a "PCV" system. The pcv valve is a check valve that doesn't have a spring. So basically full engine vacuum, is applied to the oil sump, all the time. There is a pcv hose that goes between the engine and throttle plate, to the valve cover, without any kind of spring or pressure regulation.

I suppose the next difference is that, in the two stroke, the gasoline is actually sucked through the case, and maybe the gasoline would mix with the oil, and it being a solvent, might ruin the oil. I mean... You could probably just use fuel injectors to avoid this...

At this point is seems that what was left on the table was a more efficient engine that makes more power more smoothly....

  • 1
    Is your Prius a 2-stroke or 4-stroke engine? Correct me if I'm mistaken but virtually all vehicles sold in the USA market use either diesel or gasoline engines. Both operating as 4-stroke engines. USA EPA regulations have basically outlawed 2-stroke engines in vehicles due to very tight emissions control. 2-strokes emit polluting byproducts that cannot be massaged by a combination of electronic fuel injection and catalytic converters. Only off road motorcycles can offer 2-stroke engines as well as chain saws and weed wackers.
    – F Dryer
    Aug 11, 2023 at 5:35
  • BTW, positive crankcase ventilation (PCV) valves are part of emissions controls to draw combustion blowby gasses back into the intake to burn instead of venting gasses to the atmosphere. 2-stroke engines use premixed fuel and special oil for somewhat cleaner burning, producing less smoke.
    – F Dryer
    Aug 11, 2023 at 5:35
  • Two stroke doesn't mean valve-less. Large 2-stroke marine engines have valves like a 4-stroke engine.
    – vidarlo
    Jan 6 at 17:02

1 Answer 1


The Detroit Diesel Series 71 and Series 92 engines were both 2-stroke engines utilizing oil pumps. I'm sure there are other examples. Both are fuel injected and have the intake air charge coming through the crankcase.

  • So why isn't this the norm lol
    – sergbot
    Aug 12, 2023 at 20:54
  • @sergbot - Because the lube is in the fuel? (for most 2-strokes) Aug 12, 2023 at 22:25

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