Optimum oil level=less resistance=faster warm-up cycle

Yes, it can, exactly as you imagine - less oil means less mass to heat up during the warm-up cycle. Many people put in exactly 4 quarts because of this, so it's not all the way full (4.4 qt, when the filter is replaced as well). That gives you plenty of extra to burn off, while not adding too much extra mass to be heated.

That said, the overall difference probably isn't that huge, as long as it's not overfilled. (After all, a quart of oil weighs what, maybe 2 pounds? And how much does the engine itself weigh?)

 

my mechanic regularly overfills mine by 3/8". i have never noticed any problem. he claims he puts in the amount the manual calls for.

 

Yes, the manual calls for 4.4 qts. When I fill mine with 4 quarts it is halfway between the dimples. If I were to add the additional 0.4 qts. it would be overfilled.

When I would take it to the dealer they would fill it right up to the top dimple.

 

i get 65mpg in good weather, so i doubt it is lowering my mileage significantly, but who knows? maybe i should let some out and see.

 

I always put right in the meddle mark.
c

 

Usually, I do my own oil changes and I fill to the middle between full and low, but this last time the dealer changed the oil. It seems like I've been getting better gas mileage with full oil level. My theory is that in the Gen 2's, more oil means that you can store more heat in the thermos which reduces warm-up time.

 

I thought the thermos held WATER?

 

Coolant specifically. But not oil.

 

Then so much for my theory...

 

66,000 miles we do all our oil changes. I put in exactly 4 quarts of oil and at 10,000 miles when I change nearly 4 quarts comes out.

4 quarts places the oil right in the middle or a little above the middel of the dip stick.

al

 

Beside the optimum oil level, to increase fuel economy SAE 0W 20 grade oil is recommended, 100% synthetic.
It's a kinda difficult find out this grade in Europe... Looks like the only one avaible here is Motul EcoLite 8100 0W 20, that's the one I've always used.
I know you people U.S. have more choices.. Like Mobil 0W 20 advanced fuel economy, that looks one of the best to reduce wearing and increase FE.... Well..... That's what the ads say guys!

 

I'm from Europe and bought Mobil 1 0W-20 on ebay, previously I had 5w40 and I don't see any improvement in fuel economy. But I don't really know how would 5w40 cope in this cold times that we have now in Europe.

 

I have experimented with putting in 4 quarts of oil vs. the specified 4.4 quarts and have been unable to detect any difference in gas mileage.

An important thing to consider is that Toyota, and other maufacturers, have purposely increased the oil capacity of their engines. Four cylinder engines have generally increased from under 4 quarts to about 4.4 or 4.5 quarts. I have a new car with a 4.6L V8. The same engine in my previous car held 5 quarts; it now holds 6 quarts. Increased oil capacity, along with synthetic oil, allows manufacturers to specify a longer oil change interval because it increases the amount of oil additives and lengthens the time before the additives break down. It is the additives in the oil that wear out, not the oil. The 10,000 mile Prius oil change interval is based on 4.4, not 4, quarts of oil. When you put 4 instead of 4.4 quarts of oil in your engine, you put in 9-10% less oil additives than Toyota specifies; this shortens the operational life of the oil.

Some may think that it is OK to put in only 4 quarts because so far oil analysis reports show no problems doing so. However, by the time you see a problem on an oil analysis report, the damage has already occurred. You can't go back and undo the lack of maintenance that caused it.

Even if 4 quarts results in an increase in gas mileage, which I doubt, is it worth risking prematurely using up the oil additives and shortening the life of the engine and/or higher oil consumption due to worn valve guides or rings? I think not, if you plan on keeping the car for a long time.

 

Interesting prospective. Not that I am skeptical, but do you have any references to the increase in oil capacity of engines?

 

I don't know if there is any literature on the subject of increased capacity. This is just my thinking based on what I have observed, particularly with Toyota and Ford, over the past 20 years.

My primary point is: why go to the expense and effort of buying synthetic oil, a Toyota filter, changing the oil yourself to be sure it is done correctly and then put in 10% less oil in the engine than the manufacturer specifies, based on anecdotal and contradicted claims that this will improve gas mileage, and thereby increase the risk of having a major oil related problem? Seems to me that the unproven MPG benefit does not merit taking this risk.

Here is something else to consider: If Toyota thought they could increase the advertised gas mileage by even just 1 MPG in the Prius by specifying a 4 quart, instead of 4.4 quart, oil fill, I think they would do it in a New York advertising minute. Car companies constantly battle each other in their advertising over a 1 MPG difference so they can claim to have the "Best in Class" MPG.

 

On the other hand, Toyota also controls where on the dipstick to place the "low oil" mark, and has to be willing to pay for an engine replacement if somebody runs 60,000 miles with the oil sitting right there and that makes it go kablooie. If the extra 0.4 quarts makes that big of a difference, the low oil mark wouldn't be quite so low.

That said, I probably fill with 4 quarts more because it's easier to measure than any other reason.

 

I was just curious because I was noticing this tendency. Our 06 Kia van (3.8l v6) we just traded for a Rolla last fall took nearly 6 quarts and it had a 3K OCI! What a pig.

 

Just pouring in four full quarts and not having to deal with measuring out an additional 10 or 12 ounces is probably a strong motivating factor for a lot of people. However, its not a problem if you use something like the oil bottle with a closeable pour spout in the attached picture to pour in the additional 10-12 ounces.