No Gain In MPG

let enough oil out & you'll burn it up then MPG will go through the roof

 

Are you running 10% ethanol lately

 

I think he meant burn the engine up...kill it.

Lowering the oil is usually recommended to people who have found that it was over-filled by a dealer or quickie lube place. If it's within the acceptable range on the dipstick then you're fine. As for fuel injector cleaner, I really don't think it's necessary but once in a blue moon. Most gas these days is loaded with solvents so you may not need to use it at all.

Is your mileage unusually low or something? Sounds like you have done just fine in your '06.

 

Hi Walker. Please add a bit more information here for our benefit. Were you told simply to lower the oil level or were you told to lower it to a specific point? Is it possible that you were reading posts in which PriusChat folks were complaining about dealers or oil-change places that overfilled? This has been a common complaint in the past.

The other information to add would be to link to the thread or threads that gave you the direction to lower your oil level. On this issue, I think it would be helpful to have you provide a direct link, as I find it difficult to believe you were told simply to lower the oil level in your engine, without any other reference point or direction.

I see that you started a thread a bit more than a month ago, asking for more info. I also see that Bob Wilson responded, showing you a chart that exhibited his data on an MPG gain after removing oil. See Bob Wilson's response in your thread. After this posting (and a few others that gave helpful information on how to remove small portions of oil), you then asked the question about how far below the mark to go. No one responded, as far as I can tell, but it could be that people were a bit perplexed at the question. I don't recall seeing any "direction" to remove oil to any point below the dipstick level, but I could easily have missed such a post if it wasn't in a long-standing thread.

I am certain people will take note of this, though please try to be a bit less disparaging in this regard. I see you have been a member of PC for a long time and have posted many times, and I will not attempt to lecture you on etiquette, but I will ask that you research this issue a bit more before taking such a shot at fellow members of this site.

I have a couple of questions for you:

1. The issue of overfilling during oil changes has been the subject of many, many threads. You can search these, fairly easily, to find out how others have dealt with the issue and whether there is any additional "proof" of lower MPGs. You've been asked this question before, but responded that you "have not used any search or advanced features since joining. I usually read posts and follow links." I know this was in response to a rather harsh post directed toward you, but I think there is some value to the question: Why not use the search feature?

2. The other question has to do with your 2006 Prius. In your signature you note that "This car has NEVER been to the dealer for any reason." Clearly, you either DIY for oil changes or take it to a quick-change place. How much oil do you use in an oil change and how frequently do you make an oil and filter change on this car? In other words: Are you aware of any overfilling in this car?

Hopefully, your responses to these questions will allow other PCers to give you better assistance and direction.

 

Sounds like a misunderstanding. The advice conveyed here has been to make sure oil isn't overfilled (higher than the full mark), because significantly above will indeed have a minor effect on efficiency. And it's a waste of oil.

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How old is that suggestion? High-mileage engines could benefit in years past. But now with the inclusion of ethanol in gas, you have ever-present cleansing agent.

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Weather & Traffic have an influence. So does the engine air-filter. Sorry about no response. But you could imagine how many thousands of times (literally) some of us have seen MPG posts over the past 8 years...

What you haven't mentioned is how often you check your tire pressure and what PSI they are kept at. That's naturally drops over time and will definitely cause lower MPG.

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The Search feature on this site is fairly easy to use. You can get a quick start by using the pull-down menu on the top of each page. Still, if you'd prefer, you'll do about as well just by entering a search request in Google. The results invariably include PriusChat pages. All you need to do is type in your request as a basic question, such as: "How much oil should be used for an oil change in a Prius?" In Google, this search will give you pages from John1701a's site, GreenHybrid.com, and a Bob Wilson page, along with some PriusChat posts.

Like John mentioned before, I'm sorry you haven't had responses to all of your questions, though I believe you've had enough info to give pretty good direction. I hope you are able to get a satisfactory answer now -- not only to the question of oil, but also on the issue of why your mileage has dropped.

 

If you only dropped from 54 to 50 mpg after new tires and ethanol, you are doing well. The tires will break in, but the effects of the ethanol won't go away as long as it is in your fuel.

Tom

 

In theory, lowering the oil level to half or less CAN improve efficiency in the first 10 minutes of operation, by speeding warmup of the engine (less oil to heat = slightly faster warmup).

I doubt you'll see any benefit in the warm/hot temps of Florida. Lowering oil levels is mainly for those people that live in cold areas...

 

Bob Wilson's response seemed clear enough. His chart shows that he drained an "extra quart" of oil. An extra quart of oil is quite a lot of oil and could very well pose a problem.

The dealers almost universally overfill with oil as they misinterpret "capacity" to mean the amount of refill oil to get them safely between the marks. The practical "between the marks" quantity is 3.5 quarts or less, not the 3.9L refill "capacity." Even in an ideal world 3.9 would put you at the full mark; in the real world any residual will put you above the mark. And it appears that Toyota calculated "capacity" a few tenths high to begin with. (This follows since my delivered vehicle was overfull and would have had the factory dry fill capacity in it--if it was a few tenths over, then the error appars to be in the refill "capacity" as well based on anecdotal reports.) You are supposed to be somewhere in between, not on the full mark.

What does overfilling do that might harm mileage? I'm not sure. Folks have mentioned that the crank could physically be churning in the oil and that would cause considerable drag losses. Another effect could be loss of compressible gas volume in the crankcase. This would increase the effective back pressure during the stroke because it would increase pressure pulsations on the back side of the pistons on the downstroke and decrease back pressure on the upstroke (an amplitude increase.) This would increase pumping losses on both sides of the stroke. I wouldn't expect this latter effect to be very large, but I'm not sure what interaction it would have with the emission control system either.