In a car with fuel injection, about the only thing that will let raw fuel into the crankcase is a stuck injector. Is there a puff of white smoke coming out the pipe every time the engine fires up cold ?? Can you smell fuel OUTSIDE of the engine.......like when you lift the hood and take a sniff ??
If gas is getting into the oil there are several possibilities: Valve guide Bad head gasket Piston ring problem PCV valve
If the threads are stripped and the plug will not tighten, that is a problem. Possibly the source of a fuel smell, but not as likely to get fuel into the oil. That would be the least expensive place to begin.
Note that some fuel contamination of the oil is normal if running the car short distances and cold. When the oil gets fully warm, the gas in it will evaporate out with a bit of time. After a long run with the car fully warmed up (e.g. 30+ minutes on the interstate), does the oil still smell of gas?
Not everytime i check, but when engine oil check, all time he up, owerfill oil, yerterday l put down oil about 150ml it not full oil norm
NO. No amount of "snake oil" will fix a gas getting into the oil problem. If you actually smell gas coming out the tail pipe on initial startup, then a stuck injector is HIGHLY likely. But replacing the PCV valve and inspecting the associated plumbing certainly wouldn't hurt.
Sounds like you may have an aging vehicle problem, but I believe Gen2 had more fuel entrainment expected analysis in the range of 2%. In the USA we have 5W-30 oil recommended for Gen2, and I stick with that, knowing fuel entrainment will tend to dilute the viscosity. I believe design changes (piston tolerances are tighter) for Gen3+ and less gaso will be entrained. And 0W-20 is the oil spec for Gen3+ in the USA. Maybe try Mobil-1 high mileage 5W-30 not sure.
OK I give up. Somebody else mentioned head gasket and a few other things as possibilities. I don't understand that at all. On a fuel injected engine, the ONLY place the raw liquid fuel should exist is in the high pressure rail that serves the injectors......and of course the pump and lines back to the tank. So it seems to me that if there IS excess fuel going into the oil, that it MUST be coming from the injector rail somehow. Is there a flaw in my logic ??
For a normal gasoline engine that's already warm, yes. However for a cold engine, the computer will run it rich and this in combination with the cold temperature, will cause not all of the fuel to be burnt each cycle. Most of the unburnt fuel will go out the tailpipe, but some will soak into the oil via the valves and piston rings. Once the car is warm and running stoichiometric this effect virtually disappears. Also every time the engine stops, any unburnt fuel in the cylinders will have a chance to soak into the oil via the same method. As there are many start-stop cycles in a typical drive, the Prius' oil can get fairly diluted in normal circumstances (~2% as wjtracy pointed out). Fortunately the gasoline will evaporate out of the oil when the engine is warm, and IIRC the vapor from the crankcase gets pulled into the cylinders and burnt. This is one part of the SULEV emissions requirements. All of this is why you should pull oil from the Prius for a used oil analysis only after a long drive where the engine has been warm for an extended period. In any case you're basically right; if there's more then a very minor gas smell from the oil, something's probably wrong and it's probably the injectors. Hope this helps.
It doesn't take raw fuel to contaminate the oil. And just a little bit of gas in the oil can be smelled if it has not be evaporated off by the heat of the oil. If a head gasket fails and allows passage of fuel/air mixture from the cylinder into an oil passage there will be un-burned fuel pushed into the oil on each compression stroke thus contaminating the oil.
You make some partly valid points. I say partly because the temperature inside the cylinders is a good bit higher than the water or oil temperature, such that liquid gas can not exist. That's pretty much the same for the crankcase too after the engine gets warmed up. A little bit of fuel vapor would have to condense in the crankcase to actually get into the oil.......and that just ain't gonna happen in most circumstances. The PCV system will sweep it away.
I think the OP is saying his oil smells like gas. Mine does too. I noticed that when my car was pretty new back in 07. The oil smells like it has fuel in it. I think its part of the atkinson cycle byproduct. But really never have smelled fuel in a cars oil as much as a G2. Which is why I do not go over 5K miles on a oil change.
