I've been reading threads about overfill for a while now, and here is a summary of what I have read.
1. Overfill is bad
2. Dealers don't know what they are doing
3. TSBs have been issued to educate dealers and anyone who reads them.
4. Everyone obsesses over this issue.
Here is my evaluation of these issues based upon hands on experience.
1. Sure, overfill is bad, but if you get more than about a half quart above spec. .10 of a quart is miniscule. It takes 5 of those to get a half quart. The postings I have read where there have been actual problems with overfill occur when a dealer or grease monkey shop puts in 5 quarts "like every other car out there". That will cause lots of problems. As a group, we are also seeing that factory fill is above the full dot. That seems to be standard operating procedure for Toyota in their manufacturing plants and as such, I'm inclined to believe that if they are confident on that procedure sending the vehicles out like that, it is not a risk issue for us in the real world either.
2. I have worked with two different dealers. As such both have said they put in a full 4 quarts. One was aware of the oil "overfill" from the factory and realized that the amount over the full dot on the dipstick from the factory was identical to the amount over the full mark after they did a 4 quart change. They sure seemed to be on the ball about noticing that rather miniscule detail. I bet they are doing the pre-delivery prep on these cars properly also, that is how they came to notice it. But that is beside the point, the dealers I'm familiar with are also familiar with the TSB and seem to be able to just about quote it from memory, but continue to put in 4 full quarts because the factory fill seems to be 4 full quarts. No .10 quart remainders running around their garage. That would be a horrible mess to try to keep track of and maintain.
3. The TSB covers many oiling issues. I'm inclined to believe that the more serious of the issues is severe overfill (more than 4 quarts) and incorrect oil weight. Both of those mistakes can be made by sheer idiots who do not take the time to read the spec about the vehicle.
4. Visco-compulsive is the correct way to describe this issue. There are owners out there that are pulling the oil plug on brand new vehicles to drain out "overfills" from the factory, and ending up with messes on their hands and under filled crank cases; along with a smattering of oil of which I wonder what they are going to do with it?
There are folks who swear they have gained 5 or even 10 mpg because they got rid of that "extra" oil, or put in the exact correct amount at the next oil change. Of course, what we forget is that the car continues to break in at very low mileage and as a result will continually post higher and higher mileage amounts, to a point, with continued use. The oil they removed had no effect, or at least none that I can directly trace back to .10 of a quart of oil.
For whatever the reason, I think that some in the Prius community have over thought the oiling issue. The Prius isn't a china doll. If it is Toyota has a huge problem on their hands. If the Prius and its technology are going to go mainstream it is going to have to be engineered to be tolerant of minor deviations from the norm. None of us lives in a laboratory and neither do our Prii. Therefore real world operating conditions need to be engineered into the vehicle, and from what I can tell, Toyota has done a very good job of that.
All of us here care about our vehicles and intend on maintaining them, however there is a point where valid concern turns into compulsiveness. I'm not going down that road.
