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post #1 of 18 (permalink) Old 08-21-2006, 07:18 PM Thread Starter
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Default Definitive, sourced info for oil overfill affecting MPG?

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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post #2 of 18 (permalink) Old 08-21-2006, 07:32 PM
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Where is the oil level on the dip stick now compared to where it was before the oil change?
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post #3 of 18 (permalink) Old 08-21-2006, 07:41 PM Thread Starter
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Quote:
Originally Posted by firepa63
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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post #5 of 18 (permalink) Old 08-21-2006, 08:19 PM
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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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post #6 of 18 (permalink) Old 08-21-2006, 08:30 PM Thread Starter
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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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Quote:
Originally Posted by firepa63
...when they saw your license plate, maybe they thought you wanted more oil...
firepa63...AHA...I think that's my dilemma!
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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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post #9 of 18 (permalink) Old 08-22-2006, 12:40 PM
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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
Quote:
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

Quote:
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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post #10 of 18 (permalink) Old 08-22-2006, 02:54 PM
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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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