Fuel Economy Survey- Am I Hopeless?

Hills can be brutal on mileage, especially on a cold engine. S.F. can be a very "hilly" driving experience.

Being the winter time, the blend of gasoline changes and this too can effect mileage. "Summer" blend gasoline you will get better mileage.

Your commute being "7 miles and often shorter" does not allow your engine to properly warm up for optimal results. Keeping the temperature on 76 also means the engine has to run more to keep your cabin at this temperature.

I recently discovered all of this when I changed positions and went from a 17-18 mile one way commute to a 4.4 mile commute one way. I "prided" myself on averaging 50-52.5 miles per gallon with my previous position. My new location with the shorter commute will net me 36-37 average winter time driving. This is keeping the temperature at 67-68 degrees in the cabin. (You gotta have heat in the wintertime!)

I notice the 1st 5 minute segment of a typical wintertime trip the MFD will register under 25 mpg's. The 2nd 5 minute segment will register slightly higher with the 3rd segment being where it should possibly around 50.

Your 600 hundred mile trip should have given you more "average" Prius mpg's. If you were driving at 75-80 the entire way that would reduce your numbers considerably, but not 29 m.p.g. I recently went on a similar type trip this winter and my m.p.g. for the trip was back in the upper 40's, low 50's.

I do use synthetic oil and also tend to keep my tires inflated on the high side 42/40. I hope this helps in some way.

 

I'd hold off on replacing the 12 volt for now.

I'd recommend better heater management, upper grille blocking, getting your brakes and tire pressure checked. Tell us what model and size of tires you have and maybe get your alignment checked. Maybe also examine your driving habits. If you're babying the gas pedal to stay in electric only when you actually need to get up to speed, that's not a good idea from an FE POV.

 

Agree on the first part but I can't get upper 40s, low 50s mpg doing 75-80 mph on a roadtrip on my Gen 2 Prius. No way. If I had a Gen 3 Prius w/all 4 tires being LRR, maybe....

 

If you're stopped, you can definitely hear whether the engine's on/off. After the initial warmup period, if the engine's running while stopped (and it's cold), try turning the fan off, then turn it back on. You should see what I'm talking about in terms of the engine running to provide cabin heat.

Unfortunately, when moving, you can't tell (by sound) when it's running unnecessarily to provide cabin heat. You can only tell on Gen 2 Prius by monitoring engine RPM (see above for tools that I mentioned).

I'd also make sure that when braking, you're light on the brakes, to get the benefit of regen instead of throwing much/all of it away by using the friction brakes.

Although this will throw off your readings for a tank, try this... drive around so the engine's warmed up and then go on the freeway. Use the cruise control and set it for a steady speed of say somewhere between 55-65 mph. Reset your MFD then drive at that steady speed for at least 5 mins. Then, turn around and take the same highway back, to help mitigate the effects of elevation change and wind. Tell us what the MFD reads then and what speed you maintained.

 

But to be getting 29 mpg, you would be filling your tank with over 10 gallons at each fill. With the bladder gas tank of the Gen2, and if you're not waiting until totally empty, from what I've read it would be difficult for you to put that much gas in. The most I've ever filled my Gen3 tank was 10.4 gallons, after driving 45 miles after the last pip starting flashing, at 545 miles.

 

I know what you mean about some highways near SF. I'm in south SJ and it's not that hard to maintain a steady speed when there's light/no traffic.

To your other post, it would be very interesting to compare you manual calculations (miles driven since last fill / gallons put in to take it to full) vs. what the MFD says, which you say you're resetting w/each fill up. On the Gen 2, due to the bladder tank, is its fairly normal for manual calculation to be much higher or lower than MFD readings, but it'll eventually average out and the averages will be close.

 

Check your account to see how much you paid for gas. If you know what the price of gas was you can back-calculate the gallons.

Maybe the only problem is a faulty gas gauge. :-P

 

If you went 300 miles and only put in 7.5 gallons, that == 40 mpg.

You need to calculate based on miles driven since last fill / gas needed to take it to full, and average over many tanks. Do not make arbitrary assumptions about how much gas was consumed.

Also, The Gas Gauge Says Full, But That's Not Quite True: NPR | PriusChat might be insightful, even though it's a Ford engineer talking.

The tank is rated at 11.9 gallons but can vary and it's usually impossible to have all 11.9 gallons be usable, even if you definitely got it completely full.

Do not force extra gas in. See the gas bladder: exposed! | PriusChat.

 

Right...early shut off... ok, try pumping more in. If you feel you're at or nearly at full, don't keep forcing more in beyond a click or two.

Besides the possible overfill damage (that wasn't the first and only case), some have had gasoline spew back out of the tank when overfilling. There are many reports of that.

I've never put more than 9.975 gallons in my tank and I've owned my Prius since January 06. I think I was down to 1 pip back then.

 

You should log your MPG in Fuelly. It is accurate and you can see your results in various analytical reports.

 

This is the screen shot of Fuelly for iPhone.