I just changed my own oil at the first 5000 miles on my 2008 Prius as recomended on this site with Mobil 1 Synthetic and Mobil 1 Filter following the book and adding 3.9 Qts (Just above high mark on dip stick). My mileage this past week on my daily commute dropped from 54 MPG Commuting to 48 MPG. I drained off just over half a quart today so I am just above the low level on the dip stick. I think I am around 3.3 Qts. I'll see if my mileage improves.
i did the same on my frist oil change. 3.9qts, went from 50's to low 40's. then on next oil change put 3.5, brought it back up into the 50's.
Three quarts is plenty. Try it at your next oil change and see (it's a lot easier to add a little oil than to remove it). Three is enough because the system *dry capacity* is 3.9 quarts, and about 1/2 quart stays inside the engine during a change.
I recently had the same problem. I got an oil change at the dealer and they OVERFILLED my oil, past the 2nd pip mark... i mean OVER-full.. I took it back and they protested and told me that it is standard on Prius... I did not want to argue, but I requested they take some oil out. They asked how much oil I wanted.. I told them 3.5 When I took my car home I checked and it was still at the second mark: FULL. Since then my mileage has dropped from 49-15 MPG to about 46 MPG it is really annoying.
If its right on the 2nd mark, then its fine. As long as the oil level is between the two marks, then its fine.
My "new" 2008 Gen 2 had 180K miles on it when I bought it a few weeks ago. I have been going through the "new owner mileage neurosis" ever since, slightly concerned about my battery and averaging around 42 MPG. Been practicing economical driving, of course. So finally it needed me to add a quart of oil. My mileage on a trip yesterday went up to about 51!!! I can scarcely believe that being a quart down would affect my gas mileage that much! Can anybody confirm or deny? Comment?
My experience is that when my Gen2 has oil in crankcase filled to the 2nd dot on the dipstick the following occurs: 1.) Mpg goes down; 2.) After-market oil catch catches significantly more "spoils" than when oil level is at second dot (I prefer between the dots which works out to 3.5 quarts when changing oil AND filter); and 3.) Oil consumption rises. PS My theory is that more than 3.5 quarts of oil in 1.5l Gen2 motor causes significant amounts of "windage" due to crankshaft counterweights striking the oil in crankcase. 3.5 quarts or less seems to reduce the oil level to reduce "windage" significantly.
