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I failed in a search to find an answer to what must be a pretty common question: where should the proper oil level be on the dip stick--at what point between the two holes (of course, warm)?
 

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Below the bottom hole is too low, above the top one is too high. Between the two is acceptable. Since one usually loses oil rather than gaining any (I haven't heard of any engines making oil lately), it is usually best to start at the top.

Of course if your oil level is rising significantly under the same operating temperature conditions at each sample, you may have a coolant or fuel leak adding to the oil volume.
 

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After a long chat with my service rep about the pactice of Toyota both at the factory and dealer of adding four qts. rather than the 3.9 specified in the manual he thinks the "four" gives them a more precise figure and keeps it the standard in most Toyota cars. So when I got home from my last dealer change I took a file and put a slight "nick" on my dipstick at their fill mark which is very slightly above the standard fill mark.
 

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All,

I (and many other Prius owners) always add 3.5 quarts to a Prius, not 4. This puts you a little below maximum and avoids an overfill. Overfills reduce your MPG and can cause problems by splashing oil up into the intake throat (remember this is an Atkinson cycle engine and the intake ports are open for the first portion of the compression stroke).

Besides, the Mobil 1 oil I use is expensive and this way I save a quart every other oil change (I do them myself).

JeffD
 

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oil

So, this inspired me to check my dipstick. I'm at 7,600 miles, after service at 5,000 several months ago. The oil was 1/4 inch over the top dot (furthest from end).

So, I gather from this that they overfilled my oil tank.

What do I do, now?
 

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dipstick

Does anyone have a reasonable explanation for that? Why is it that people on this site know what the optimal level of oil should be—but Toyota doesn't?

Also, apart from Dan's brilliant suggestion(!), what am I to do about the oil level now? How much is it affecting my MPG?
 

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I am a retired fireman. I am also a lisenced aircraft mechanic and a liscenced master electrician. From 1959 to the present day I own and opperat a fleet repair facilities in the Denver area. I have attended numerous automobile company and after-market equiptment manufactures schools over the years, and I have yet to hear one of them say that overfilling the oil reservoir 1/10th of a qt would shut down or destroy an engine. If it does my prius is ready to die from excess oil. Sence the first oil and filter change on the prius I have installed 4 qts of synthetic oil in the crankcase. I drive in the mountains, city and high speeds on highways and have yet to experience a problem. I average 45 to 49 mpg. I would like to have access to one of these vehicles that have been harmed by this 1/10th of a qt of oil and see first hand how they were damaged. I'm always open to learning something new.
 

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The overfill is typically a 1/4 of a quart, or 25%. When you see your vehicle overfilled, try siphoning it down to the fill mark and see how much excess was really in there.

Ask for 3.5 quarts and it is pretty much on the money, or slightly under the full mark.
 

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If you are refering to the entire capacity, correct. I was looking at it from a quart. I probably shouldn't have done that.

However, if you have a 2 liter bottle, it doesn't matter if you try to put 2.1 or 2.9 liters in, it's still too much and will spill over.
 

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DanMan32 said:
However, if you have a 2 liter bottle, it doesn't matter if you try to put 2.1 or 2.9 liters in, it's still too much and will spill over.
I have never seen a 2 liter bottle that was filled to the brim. They always have a little of room left over. I'm guessing that the same is true here. If they come filled from the factory, a little over the fill mark, then I'm sure it isn't a problem to be a little over. I'm sure they have some margin for error to keep people who mistakenly add 1/4 of a quart too much from harming their engines.
 

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The overfill is typically a 1/4 of a quart, or 25%. When you see your vehicle overfilled, try siphoning it down to the fill mark and see how much excess was really in there.

Ask for 3.5 quarts and it is pretty much on the money, or slightly under the full mark.
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.The book says the capacity is 3.9 quarts and I expect the factory put the top mark there on the 300,000 cars made. So, 4 qts. would be adding an additional 1/10th of a quart. I can spill that much on the engine before I get to the "fill" hole. That's why I let Toyota put in the four quarts that they charge me for.
Boy, do we like to make mountains out of "mole" hills!
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