Join Date: Feb 2005
Location: Eastern Washington State
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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.
It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Millenium Silver Metallic (color code 1C0) over gray, package 5 (AI)