Dash MPG different than Actual MPG different t

The MPG Avg is alot like the gas guessing gauge, just an estimate. It will either be higher or lower vs calculated manually. I did 338 on 6 gallons while my display reads 51.4 MPG Avg. But by hand it's actually 56.3 MPGs.

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I have never seen or experienced this to be true of a Prius. The displayed on all 4 of my (2 current, 2 past) Prius have always shown high compared to calculate mpg.

I would agree that the displayed could be roughly estimated to be 2-4 mpg less than calculated, but not the opposite.... Just my experience over the years

 

I guess gen 2 calculated mpg could vary wildly from displayed, to either side, due to the complexities of the bladder tank. But yeah, over 2 or 3 tanks, those variations will cancel out, and you're left with the very consistent positive bias.

 

True! I never considered the craziness of the bladder tanks of the Gen 2's.

But, wasn't the op posting in a Gen 3 thread? I could be mistaken though..

 

True, missed that.

My take, no matter how many mishaps you encounter, say your good samaritan son shoots $10 in, you have a finicky pump, whatever: as long you can keep track of how much gas went in, eventually, spanning multiple tanks, you get back-on-the-beam.

That's one reason I tend to fill up as soon as it's below half full: I want to be the one doing the tank up.

 

Therefore, with any generation, the most accurate estimate we can have of true mpg for any one tank-full is neither what the display says nor distance divided by raw pump reading. Instead, that best estimate is what the display says, TIMES a correction factor based on several consecutive fill-ups. For my car, for example, that factor seems to be around 0.950 to 0.955.

 

30% variance from displayed to calculated mpg? Wow! Something has to be wrong. I never saw worse than 9% off during the dead of winter, avg was around 7% on my Gen 3's...

And it is possible to actually get 31 mpg in a Gen3 if you drive it like a madman and only do very short trips on under inflated tires...??

 

Check your 12 volt battery first (crappy mpg is most often a good indication of a dying 12v), then add a few pounds of Air to your tires... For starters.

 

Severe mis-alignment could increase rolling resistance , but you should see odd , uneven wear patterns on the edges of your tires. This factor can be negated by a true 4-wheel alignment but that costs $100(?) at the dealer.
Otherwise, it comes down to checking each fluid and operational component of the HSD system, a tedious task.

 

Reset one of the trip odometers, and run about 10 tanks through the car. Add up the total gas used, and divide it into the miles. If the mpg readout shows anything other than about 4-8% higher than your actual mileage, something is wrong with the electronics involved in the readout, or the odometer.

As I remember, the trip meters only go to 999.9 miles and start over, so you'll need to keep track of the thousands to do this.

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Could someone have syphoned gas from your tank? That would hurt actual gas mileage, without affecting the readout.

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Are you asking me (since you replied to my post twice) or the OP whom I was attempting to reply to..??

But yeah, something is up with the op's car? I have no clue...

 

Sorry, I was really replying to the original poster.

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Siphoning is nigh impossible now I think.

Regarding calculation of tank mpg, if you want to be sure, use the odometer, not a trip meter, it's "safe as houses". The trip meter is prone to accidental reset.

For sure use the trip meter, but just for a feedback, and as a cross check when doing the math with odo.

 

Yeah, to syphon you'd need access to the car to open the gas door, or break the gas door. I don't know what hapoens with the hose, re. the bladder thing.

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Do you always fill up at same station ?? Might try another station as their PUMPS might be off ,,, of course by accident of course ,,, I had 2 bars showing , filled up OMG it took 10.3 gallons ,,, I'm guessing , that's how they paid for their new car wash ,,,

 

That is the inverter output (analogous to the charging system of a traditional non-hybrid) voltage, not the battery voltage.

Measure the battery voltage when the car has been shut off for several hours.