What happened to my MPG? Differences in reported tank average MPG.

[Manchesterlover]

New to Toyota Nation and am hoping someone can help me out or point me in the right direction.

So I bought a 2008 Camry Hybrid in February and have been loving it since. I have been averaging roughly 475-480 miles per tank, this with the ac/heat and charging my phone.

My MPG from my last tank of gas however just dropped like a rock. I barely got 400 miles to the tank. At the same time the speedometer's HUD of average tank MPG and the navigation screen's MPG started to differ wildly. In the past there was a 0.1 MPG difference at most. I noticed that the HUD is anywhere from 2.5 MPG under to 1.5 MPG over the reported MPG on the screen which remained in the 31.1-31.3MPG range.

Since I was almost due for an oil change anyways, I took it in to the Toyota dealership on Friday to have it looked at and have the oil changed. The response I got from them was less than stellar. They blamed the 16% drop in fuel effeciency on bad gas, cold weather and using the ac/heat. While I do understand totally how and why those things affect the effeciency, it doesn't explain the discrepencies in the MPG the car's computer is reporting. The dealership couldn't explain it and even tried to tell me that the nav screen's MPG was the car's lifetime value and when I called them out on it they then stated it was the trip value, which I know is completely wrong since I reset it after filling up.

Furthermore, after yesterday, which was the first real day of driving, I ended with the following results.

Start of day
Trip odometer + Cruising range = 475
Speedometer HUD MPG = 31.5
Nav Screen MPG = 31.1

End of day
Trip odometer + Cruising range = 454
Speedometer HUD MPG = 32.5
Nav Screen MPG = 31.6

How is it possible that the computer is showing better MPG while at the same time decreased total miles? To me that doesn't seem logical. At this rate this tank of gas will be in the 400 mile range again.

One side note, I did have the bumber on the vehicle taken off and repainted due to an idiot on a cell phone rear end me and that's when I really started to notice the issue. Is it possible that the body shop do something to the car while fixing it? I know that they left the car on without driving it when I got it back based on the nav screen's minute by minute MPG.

Thanks for your help.

[snookwhaler]

I know there are a lot of variables here. Start with the basics. Recent oil change? Tire pressure? New tires? Alignment? Mis-Alingnment? Parking brake dragging? Air filter inlet obstruction (bird, birds nest, bugs, etc...)? Eco button not engaged? Etc....

Have you ever replaced the original AGM/accessory battery in the trunk?

[ukrkoz]

i'd say it's about right though.

I have "lifelong) average mpg set on nav unit. right now it's around 38.2 or so.
donno what you call HUD, but tank average always varies from nav average. sometimes it's better, sometimes it's worth. I simply do not pay attention to it, as lifetime on nav is considered being the only true one to look at.

MPG DROPS BADLY TOWARDS COLD TIMES. period. mine went from 42.5 last summer to 35.2 winter, then crawled back to 38.9 by august again. any temperatures lower than 55 kill mpg.

so, really, you should be more concerned about generally crappy mpg. I had 28 average on a Ford Ranger pickup truck. yours is not far from it.

[Manchesterlover]

Since the original post, I have discovered/realized a few more things that may explain what is going on with my car, but I won't be able to really validate it until I fill up my tank and calculate the MPG.

First off after talking with Toyota Customer Care, I learned that the information on the Heads Up Display (HUD) in the center of the speedometer and the information on the Nav screen are apparently calculated by two different methods. And as such they won't be identical even though I never realized that they could be as much as 20% different which to me seems ridiculous. Unfortunately, I couldn't find out which one calculates the MPG more accurately. Also, Toyota Customer Care is supposed to get back to me to let me know if it is possible to restore the Nav or HUD computers to factory defaults in an effort to get more accurate readings. Also, the calculated MPG can be as much as 15-20% more than the real MPG when calculated the old-fashion way.

Ukrkoz, I don't understand how you can have a lifetime MPG on your nav screen unless your car has different firmware for the nav unit or you have never hit the "Reset" or "Reset All" buttons.

As far as the oil change last Friday, the dealership put 5W30 in and jacked the tires up to 40 psi. Since then, I have managed to increase the calculated MPG on the HUD to 33.6 and the nav to 32.1. However, let's wait to see what the real MPG gets calculated at.

The 400 miles/tank (28 MPG) could be a fluke. It's possibly from low tire pressure, but more likely the fact that the auto body shop left my car on while they were working on it draining the battery forcing the ICE to kick in to charge it. When I picked up my car I do remember that the minute bar consumption graph was uncharacteristically low, but don't remember exactly how bad it was.

This all being said, I'm curious what people in the Pacific Northwest or similar climates get in terms of gas mileage and what oil you use and what tire pressure, extra. Ukrkoz, I see that you are in the PNW, what are you doing to get such good gas mileage?

[rainbowchaser]

A few comments: Take the car back to the dealer and have them do a free oil change with the recommended 0W-20 or 5W-20 oil. There is no place for 5W-30 in a TCH (well maybe in a box in the trunk, for another car). Even the oil filler cap tells them that. 5W-30 would also adversely affect fuel mileage.

Also, unless you don't care about tire wear, having the tires closer to the recommended 32PSI than the 40 the dealer set would be better.

For most of us, it is typical for the nav fuel mileage to be 3-5% optimistic compared with hand calculated (miles driven/gallons filled).

It does seem you are getting more variance between the HUD (really not a HUD, but a Driver Info Center - DIC) than I see, but I can't explain why. Also, a drive of 20-30 miles is really too little to get a good handle on the changes.

I would also see a significant 2-5 MPG drop in fuel mileage going from New England summers to winter time.

[jjsc]

Here in California, I see this behavior every winter. The two main
reason for the drop in MPG are:

1) Gas changes to winter mix - By law, gas stations are required to
add ethanol to the gas to lower pollution. This also decreases the
energy density of the gasoline, resulting in fewer miles for the same
gallon.

2) Your engine spends more time running at lower temperatures (inefficient
operating conditions).

-jjsc