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For my most recent service, Toyota overfilled the oil by .3 qts.--4.2 qts.--instead of the owner's manual recommended 3.9 qts., with filter. Before this oil change (with the oil level right at the fill level), I had gotten 58.9 MPG. The first tankful since the change netted 55.3. This was in driving conditions that weren't as favorable, but I would have still expected a little better. The second and most recent netted 57.1. These driving conditions were very close to the one before the oil change. I would conclude I'm losing about 1 to 1.5 MPG as a result of the overfilling.

I've read a great deal on here about how overfilling causes a loss of MPG and it makes sense with posts stating more oil having to chug through the crankcase, etc. I don't need a series of confirmations on that. All I want to know is if there is a definitive, accurate statement that overfilling causes loss of mileage (my example above will help, but it's not definitive) that I can show to my dealer so they won't roll their eyes when I ask them to remove .3 qts.
 

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Discussion Starter #3
firepa63 said:
Where is the oil level on the dip stick now compared to where it was before the oil change?
If you compare the increment between the hole at the end of the dip stick with the top hole (which I assume is a one quart increment), which is the fill point, it is .3 qts. above the top hole--about a 1/2".
 

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I would say this is far from definitive. There are too many other variables to conclude a drop of less than 2 MPG out of almost 60 is the oil level. I vary by that amount on tanks all the time under what I believe to be "similar" driving conditions (regular commute route, followint the speed limit, temps, etc.) and the oil level remains constant across them.
 

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Mine was overfilled about the same amount one time. I lost about 3 MPG. However, since it was not high enough to damage the engine, I didn't have the dealer drain any. The next oil change I had the service manager look at the level before the oil change and told him that if the level wasn't where it should be after the service, they would be draining the crankcase. I never had another problem. That was about 2 years ago. For the little bit you are over, I wouldn't bother draining any.

Also, when they saw your license plate, maybe they thought you wanted more oil... :)
 

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redwein, you could be correct...it's fairly negligible and not easy to tell, given many factors...still, mileage fanatic I am, I can't help but feeling there's a difference.

But I'm still hoping someone can answer my original question.
 

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I did search "overfilling oil poorer mileage" and got some hits confirming it, although none really stood out. I guess its pretty clear then. So I should do what firepa63 says and next time warn them beforehand that if they go past the fill mark, they will drain it.
 

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US TSB EG050R-04
December 20, 2004, Jan. 13, 2006 revision. ENGINE OIL SPECIFICATIONS. 2001-2006 Prius. (Incorrect engine oil viscosity or improper fill level may result in a M.I.L. "ON" condition (most common Diagnostic Trouble Code P3191 "Engine does not start"). Use SAE 5W-30 API grade SL "Energy Conserving" or ILSAC GF-4 oil and use proper fill quantity.)

http://autos.groups.yahoo.com/group/toy ... 50R-04.gif
or
http://autos.groups.yahoo.com/group/toy ... 50R-04.gif
or
http://www.alldata.com/tsb/Toyota/11371 ... /5004.html


Then there's this page:
http://www.fueleconomy.gov/feg/maintain.shtml
Use the Recommended Grade of Motor Oil

You can improve your gas mileage by 1-2 percent by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1-2 percent. Using 5W-30 in an engine designed for 5W-20 can lower your gas mileage by 1-1.5 percent. Also, look for motor oil that says "Energy Conserving" on the API performance symbol to be sure it contains friction-reducing additives.
and: http://oee.nrcan.gc.ca/transportation/p ... attr=8#oil

Most engine oils sold for light-duty vehicles are multigrades, such as 10W30 or 5W30. Today's vehicles are generally designed to use 5W30 oil year-round, although some manufacturers are beginning to specify 10W30 oil. Older vehicles often need 10W30 in summer but can switch to 5W30 in winter. By using the lowest multigrade of oil recommended in your owner's manual, you can improve the fuel efficiency of the engine, particularly when starting it cold.
But that's not so much overfill, but the wrong type of oil...

I did find a few sites that stated that too much oil is bad, but nothing from an "official" source.
 

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I expect that it all goes to the terminology And what is "overfill?" Seven quarts! probably too much, 3.5 qts. and the imagining that it gives better gas milage??, 3.9 specified in the owners manual which should indicate "full" on the dipstick, and the 4 qts. put in by the Factory and the dealer which indicates a "shosh" over full on the dipstick.
What ever the owner wants to do to make the car perform better in his own mind whether it does or does not. From stiffening plates for the suspension system, high tire pressure and low oil quantity for better milage figures, there isn't much else you can do to modify these cars.
If your imagination is great and you have deep pockets you can even start playing with several hundred brands of new tires. (And don't forget the nitrogen)
 

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The problem that we have with oil "overfill" is not the fact that the sump is overfilled, because a 4qt fill is not a problem. The problem is Toyota converting Metric straight over to English without taking into consideration that the english system of measurement is not decimalized. Which means that anytime you do a conversion between Metric and English you end up with fractional differences between what otherwise should be even fluid fills that have to be represented by decimals.

Toyota should have looked at how the US market purchases oil. They would have determined that writing the books to indicate that an even 4qt fill would be easy to acomplish for any grease monkey or shop and reduce confusion among owners. This fractional sump volume has been a thorn in the side of dealerships and owners since day 1. Over the past 19 months of ownership I have had 4 oil changes, all of them a full 4 qt fill. And the drop in FE I have seen has been negligable and has only affected the tank in which the oil change occured. I attribute this to the supid procedure of revving up the enging after doing an oil change by some oil change places, and other places that do a short test drive after the oil change is done. In other words, it isn't oil quantity, it is the driving habits of those that have the vehcile when it is not in my hands.

I would really like it if somebody who aserts that a 4qt fill on an oil change drops FE would detail how a .10 of a quart is affecting their FE. I've heard crank slap as an issue, and yet a cross section of the engine indicates that the crank is many inches above the highest point of a 4qt fill. In fact I would estimate that it would take 5qt+ for crank slap to occur and that would cause severe driveability issues and the driver would notice it immediately. Beyond crank slap, I can't think of anything else.

Drag on oil pump? No. Because the oil pump intake is always pulling oil from the lowest part of the sump and the pump can only take in so much oil at any given time based on the size of the intake and the volume of oil that the pump can move per revolution of the pump mechanism. In other words, the operation of the pump is totally unlrealted to the sump level.

My creative juices are not running well right now, but suffice it to say, I can't think of anything that a minor "overfill" would do to cause any change in MPG.

The jury is still out, but I don't think they are going to come back in and post a verdict.
 

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First off, even at 3.9 quarts, you are still over the full mark of the dipstick. 3.5 quarts puts it just right.

Second, where do you find a cross sectional view of 4 quart fill in relation to the bottom of the crankshaft? Do you actually have a clear plastic oil pan? Or maybe transparent aluminum.

I would agree though that we really don't know without being able to see where the fill line is and how close the crankshaft becomes. Our tests and suspicions admittedly aren't scientific.

But the crankshaft doesn't have to actually hit the oil level to cause drag, since oil is a fluid and will be affected by the motion of something just above it.
 

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Discussion Starter #14
DanMan32 said:
First off, even at 3.9 quarts, you are still over the full mark of the dipstick. 3.5 quarts puts it just right.
This statement would contradict the owner's manual stating that full is 3.9 qts., including the filter. According to that, 3.9 should be on the fill mark. If what you say is true, Dan, then I actually have about 3.8 qts., being .3 above the fill line. Whatever, I'm taking my car in on Tues. to have the wheels balanced and while there, they will drain it to the fill line.
 

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wayneswhirld said:
DanMan32 said:
First off, even at 3.9 quarts, you are still over the full mark of the dipstick. 3.5 quarts puts it just right.
This statement would contradict the owner's manual stating that full is 3.9 qts., including the filter. According to that, 3.9 should be on the fill mark. If what you say is true, Dan, then I actually have about 3.8 qts., being .3 above the fill line. Whatever, I'm taking my car in on Tues. to have the wheels balanced and while there, they will drain it to the fill line.
The reason 3.5 quarts is about the right amount is that you can never get all of the oil to drain out. If the sump was completely dry, 3.9 quarts would be the correct amount.
 

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What a pain in the butt that must have been! (I would guess then that the "full" marks put on the dipstick by Toyota are not at the 3.9 position?)
I wonder why they chose to mark the dipstick at 3.75?
One other observation: 4 qts of oil is much closer to the 3.9 full quantity specified as "full" by Toyota than is 3.75.
 
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