Since i bought the car in november last year i have been putting 0w20 from ENEOS(good quality oil), and not knowing what kind of mileage to expect i thought 6.5l/100km of LPG was kinda cool, the only down side to this oil was that it was consuming it like crazy ,2 liters between changes, hazardous for the engine. For that reason i decided to go with somewhat thicker oil, 10w40 mos2 from LIQUY MOLY. The end result is kind of impresive: the fuel consumption went down to 4.8l/100km of LPG (very cheap stuff - 2.5 $/ 100km) on the same driving style, mostly city, the engine is quieter and the oil consumption is almost gone, and when i say "almost gone" i mean half a liter of oil is missing between changes. I recommend it for high mileage engines or oil consumption problems. On my next oil change i want to try Xado's metal conditioner and see what's what, maybe even lower fuel consumption or/and no oil consumption at all .
It says in your info that you have a 2005 Prius. The correct oil is 5w30, so neither what you had before nor what you have now are really OK. Try with fully synthetic 5W30 and see what the fuel and oil consumption is like, I suspect especially it will use less fuel.
Cosmin is apparently using non-traditional fuel (LPG instead of gasoline) and lubes so all we can do is appreciate the info. Might be of interest to other EU LPG users.
everything I have read about lpg says that it burns much cleaner than gasoline, leaves no deposits in the combustion chamber, and doesn't foul the oil and turn it black. I wish I had that option without major expense and hassle.
The oil that i have used 0w20 was a premium fully syn and i think any kind of oil that fluid would be consumed over time and since i have results with this one its a keeper.
Lpg does burn cleaner than gasoline but it requires a good oil. About the cost of lpg injection system is about 600 euro installation included and you have two extra filters to change every 20000 km but considering the price difference between fuels you will brake even in a year or so depending of how you drive and the mileage that you drive every year. I belive lpg is closest in fuel consumption to plugin conversion for a quarter the cost.