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I've noticed that sometimes I will either coast or be moving very slowly, yet I only show about 50mph. Does it having something to do with the engine not being heated up? I have had this at all times of day, but mostly after I start up.

some day, I'd like to see an avg of over 45mph. I've had the car for 7,000 miles and still haven't see that. Guess, being in NJ and driving mostly locally, all I do is stop and start and stop and start and stop and start!!!

David
 

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drtravel47 said:
I've noticed that sometimes I will either coast or be moving very slowly, yet I only show about 50mph. Does it having something to do with the engine not being heated up? I have had this at all times of day, but mostly after I start up.

some day, I'd like to see an avg of over 45mph. I've had the car for 7,000 miles and still haven't see that. Guess, being in NJ and driving mostly locally, all I do is stop and start and stop and start and stop and start!!!

David
David - do you mean mpg instead of mph?

Be sure to check your tire pressure - low tire pressure will hurt gas mileage.

Also be sure to check your oil level - it should be below the full mark - if it's at or above the full mark, that will also hurt your gas mileage. My gas mileage went up almost 10 percent when I changed the oil at 5K miles.

If your driving includes a lot of short trips with the car turned off while you're in a store, then your gas mileage will suffer. Not too much you can do about that but be sure to check your tires & oil level.
 

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For at least the first 5 minutes of your drive (assuming that you don't have an EV button in use), perhaps as long as 20min if it's cold out and the car has been sitting outside all night, the gasoline engine will run just to warm itself and other emissions components (like the O2 sensors and catalytic converter) up to proper operating temperatures. (At least in the Classic Prius you had the blue cold coolant light to tell you that this was happening...) Prius will put emissons before MPG. Also, if you are requiring heater use, that will draw "waste" heat away from the gasoline engine, making it run more often to warm up. For either of these scenarios, the engine use will not show up on the Energy Monitor. (If you have a Classic Prius, the front windshield defroster uses the AC compressor, and as you may already know the AC on the Classic Prius is belt driven off of the gasoline engine, so the AC compressor use will cause the engine to run more often, and again it is not on the Energy Monitor...)

Start and stop/short trip driving will yield low MPG in any car, not just the Prius. This is not the driving style that the EPA lists as "city" driving... With the same driving style, what was the MPG in your previous car as compared to the EPA ratings? The ratio should be similar for both your previous car and the Prius.
 

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oops

of course I meant to type MPG, not MPH. I'm lucky I didn't confuse MFD with the above 2 abbrevs.
 

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CinciPrius said:
Also be sure to check your oil level - it should be below the full mark - if it's at or above the full mark, that will also hurt your gas mileage.

I probably missed earlier discussions on why overfilling the oil causes a decrease in MPG. Anyway, in my case, this may be true but only slightly. I had just had my best average tankful MPG of 55.6 in early Sept. before I had the 5,000 mile service. During the servicing, I mentioned to the Toyota service manager that I had read at Prius forums that there was a tendency to overfill on oil changes. He said they use an oil drum, not individual cans (may be common practice at all dealerships) which could lead to overfill, but he said they are pretty careful with that. Well, I should have checked the level before I left, because when I got home I saw it was about a 1/4 quart overfilled. I have not done anything about it. But my mileage has decreased just a little--despite an increase in tire air pressure around that time to 38/36 from what was 30/30. Since then in the same type of driving it has been 51-54 MPG. So perhaps the increase in tire pressure has almost offset the slight oil overfill. Again, another factor could be cooler weather although the AC hasn't been on much after the oil change--another offsetting factor. With all this, I estimate I'm losing about 2 MPG because of the overfilling. Maybe I should go back there and make them drain some out, though it's 30 miles away in the opposite direction I usually travel (I haven't tried changing oil myself for 8 years).

But again, what's the technical explanation for this occurring?
 

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We can only speculate, just as we can only speculate on the mileage actually suffering when oil is over the full mark.
By the way, did you check to see if it was over the full mark before you had your 5K oil change? Most of us found it over right from delivery.

I would suspect that the oil reservoir is reaching the crankshaft. That's the only plausible explanation I can think of. Nothing else is really down there.
 

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CinciPrius said:
Also be sure to check your oil level - it should be below the full mark - if it's at or above the full mark, that will also hurt your gas mileage.
Lots of folks have reported mileage increases at 5k. The reason has less to do with oil level and more to do with the natural break in of the vehicle. Now, Toyota products are very well engineered and the tolerances of manufacturer are very tight, so break-in isn't so much a special period of use where you have to treat the car differently, however it is more or less the period of time where the moving parts of the vehicle set in to a natural orientation, alignment, placement or however you want to describe it.

Now, most of us have experienced a couple different stages of "break-in". I know I noticed the car becoming more efficient before my first oil change, around 3k. And as I approach 10k I notice greater efficiency just about every time I fill up, although it is starting to plateau. I keep my tires at 40 front and 38 rear and usually check them about every 2 weeks and adjust as necessary.

But here is the real kicker with regard to my experience. My oil has always been "overfilled". What is overfill? Well, some define it by the marks on the dipstick. I find that entirely questionable because a dipstick is not a precision instrument. It includes no specific graduations indicating oil height in pan or indicating specific volume in milliliters. It is just 2 dots embossed on a metal rod which is supposed to give us a general idea of how full the sump is.

If the dipstick were a precision instrument I would take it very seriously, however it is there to give us a general idea of the safe level of oil in the sump, not to give us a specific measurement of oil in the sump.

Oil overfill would have a negative effect on FE if the sump was so overfilled that even when the oil system was pressurized there was oil in the sump that was being struck by the crank as it spun. That would put resistance on the crank, along with creating a situation of oil foaming because the crank would be hitting the oil in 4 places very quickly and thus agitating the oil as if it were in a blender or food processor. In fact, if oil overfill was such that this condition was occurring, it would be a short time until the possibility of engine damage occurred. FE would be the least important problem that an engine overfilled to this level would be suffering.

So, the book volume of oil in the sump is 3.9 quarts; which is 3.690 L. 4 quarts is 3.785 L. That is a difference of .095 L and .10 qt. That isn't enough liquid to appreciably change the oil level in the sump so that crank strike happens, let alone an oil foaming issue or even a loss of FE.
 

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But I was able to extract .25 quarts to get it down to full. If we all had different levels showing, I might agree that the dipsticks are not accurate, but we all get about the same overfills.
 

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Whatever the true indicator of the state of overfilled, thanks, especially to jeromep, for the detailed explanation. And apologies for not starting this as a different topic.
 

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I doubt it would be a smidgen. If 3.5 quarts shows .25 quarts short of full, about 1/8" below full, then 4 quarts would be 1/8" above full.

Hmm, guess that is what they are all doing. But 3.75 should be just right.
 

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"And as I approach 10k I notice greater efficiency just about every time I fill up, although it is starting to plateau. "

I would attribute this to "driver break-in" where your driving style changes as you get used to the HSD/CVT power curves, very different than a normal ICE/auto tranny combo.
 
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