Suddenly poor gas mileage

It's been hovering in the plus/minus 0 F in Northern Wisconsin. My ten mile trip to work is hovering in the low to mid forties even with the lower grill blocked. Right now I get better mileage on the highway. But, I know that will change.
Hang in there.

 

Those are not silly questions but they are hard to answer accurately.

The time it takes to reach full operating temperature depends on a few factors.

#1 Ambient air temp
#2 Temp of the engine coolant at startup
#3 How aggressively the car is driven during the warm up stage
#4 Weather conditions during warm up stage (dry, rain, high winds, etc.)

My morning commute conditions are similar to yours with respect to temperature. I leave my apartment with the coolant temp right around 60-90deg (car sat overnight). I turn onto a main street and accelerate briskly to 40mph then brake rather sharply for a stoplight. I make a u-turn then drive for approx. 1mile at 50mph before turning onto a freeway. I enter the freeway and maintain 65-70mph speeds going slightly uphill. I always watch my temperature gauge and I usually reach 170-180deg (approx. operating temp) within about 4miles or so of total driving. I can cut this time/distance down slightly by blocking my grille but because temps in my area rarely drop below 30deg F, grille blocking is not super effective like it is in other climates.

Bad weather can increase the time it takes to reach proper operating temp.

Water from rain wicks more heat away from the radiator and engine block. High oncoming winds push more air across the radiator and engine block wicking away heat. Because the Prius engine is aluminum and so small, it has a hard time retaining heat so the better insulated it is during the warm up stage, the faster you will reach proper operating temperature and go into closed loop mode. I'm not going to comment on open loop vs. closed loop until I do more testing.

So in your case I am not sure there is much you can do to improve your efficiency besides grille blocking or install and engine block heater. It's worth a shot but the former doesn't seem to help me very much. IMO people with very short commutes are in a tough spot. They are going to get lower MPG no matter what they do. This is where options like the PriusEV is going to make a huge difference for people who have short commutes but want want a versatile car that can get great MPG in all settings.

 

The gen3 ('10/'11) handles warmup better imho than the gen2. We can hold 50 mpg over a tank with our 1.5 mile commute (car garaged, lower grill blocked in winter) (max psl=40) (psi=44/42). It will drop to 40 mpg in extreme cold (<~5F) and/or snow. I don't really need stage 4 per se, to hold these mpgs, just need to get to stage 2 or 3. Stage 1 is a killer with the timing past top dead center.

 

I highly doubt you could do so unless you drove enough extended trips where your MPG was higher. I find it hard to believe one could achieve a 50mpg tank comprised of only 1.5mile trips.

 

I never said the tank only had 1.5 mile trips; I said with 1.5 mile commute. Yes, we have some 5 mile and sometimes longer trips, but we also drive .25 mile for lunch, etc. Our lowest calculated mpg for a tank was last winter at 40 mpg, covering sub-zero and single digit temps and snow/slushy roads, and defrosting at times.

This winter, I have the Prius on a BatteryMinder during the snowstorms because the Prius is clean at the moment, and we are using an older car until the roads clear. But even in winter temps the current tank is at 51.3 mpg MID (~48.5 actual based on average MID error).

About synthetic: The spec is for 0W-20. 0W-20 only comes in synthetic. Next change, give it the proper viscosity and the synthetic question is moot. Then enjoy 10K oil change intervals.

 

You block the lower grill by buying 2 8' lengths of 1/2" pipe insulation at the home store, cutting 2 pieces from each and stuffing in the 4 openings. Cost ~$2 total.

Get a scanguage II to monitor coolant temps or at least review the grill blocking thread for the gen3 to see what ambient temps indicate less than 100% lower grill block.

 

You know more about getting the most out of a tank than I do but I wanted to tease more out of your post that was not written. Otherwise new readers will expect to get 50mpg tanks regardless of how short their commute is. That is not helpful to anyone.

jfountain2, No. You should not run the car unless you are going somewhere. You can play all kinds of games with the reset button to make your MPG number look better but any time you run the car without moving you are getting 0mpg and that is never good. Period.

 

You should not leave the car on. Just get in and drive. Some argue to idle in Stage 1a (~first minute), but that is the only exception. Of course, if you need heat to defrost before proceeding, then let it idle accordingly.

 

Grill blocking greatly speeds the warmup in my experience.

 

Your point is well taken F8L. Not everyone has 20-40 mph psl's all the way to work with pretty flat terrain and reasonable traffic. And not everyone will work as hard as me, but this is my wife's daily driver and she just drives it, though she has good sense about driving efficiently.

 

I'm having the same problem, only worse. I live in Florida and was getting 66-54 MPG city when I purchased my Prius in Feb. of this year. 2 1/2 weeks ago the mileage dropped down to 38 mpg, then 34, now I'm only getting 23 MPG. I haven't changed my driving habits at all except to run the A/C occasionally (same routes as when I was getting 66-54 mpg). I've called Toyota and asked what could be causing this problem; they said that there are no known issues with the 2010 model, so I'll have to bring it in (hard to do since I work 60-80 hour weeks with no weekends, and the dealership is 45 minutes from home). Obviously I'll have to get it to them, but I'd really like to know if anyone has had the same problem in warm dry weather. I've gone through almost half a tank of gas in a week while driving 30 minutes or so a day. It took me three weeks to burn through that much fuel when I first purchased it.

 

If I didn't know better maybe you have a leak in your
fuel system.

We have over 47,000 miles on our Prius. Even in the winter with
35-45 degree weather, rain pouring down, we always average
at least 40 + MPG. The worst ever was about 40.8 MPG, calculated.

In summer MPG is almost always over 50 MPG's, calculated.

al

 

Otowner, not sure where you live (going to guess Orlando). I am from Jacksonville though, and I get no lower than about 50mpg. Average for the last 2 tanks is 55mpg, with almost 3500 miles on the car itself (purchased in February). My commute in the morning is about 11 miles long, with half of it at 35mph or below. The other have is 45mph (I drive it at 50 though).. So I wind up having the ICE off quite a bit.. I have noticed though that sometimes when the ICE is on, and the battery is at full charge I will feel the car jerk a little. Then my MPG gauge will drop from above 50 to somewhere in the 25-30 range, and show the arrows going into the battery instead of the battery helping the engine out.. Not sure what could be causing your problem though. We drove from here to Orlando and back last Saturday getting between 50-60mpg the whole way on I-95 & I-4.

 

Copy and paste the questions found in the link and answer them, with more info people here can pinpoint potential issues and help you with them.

http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html

 

Ya know, your car is still under waranty, don't you? So, they are going to give you a free loaner - right. How does working 80 hours a week impinge on a 55 minute travel and exchange of vehicles at a dealership?

At least they let you work on weekends. When I had an 80 hour a week job, it was all during the week. I didn't really have weekends either, as I spent them sleeping after a few months of that.

I am not from Florida, or have never been there, but where in Florida is it "dry"? From the acquantances I have had from there, they say its humid, all the time, every where in Florida.

 

The Toyota dealers I've gone to typically do not give free loaners for warranty work nor maintenance.

I've only gotten one once (received a HyCam), when they had to keep the car overnight to (IIRC) repro the squealling CHS pump problem. I had to return to the dealer after work to pickup the loaner when they couldn't repro the problem during the day.

 

That is extremely low
I get lower than average MPG due to poor driving conditions short trips, steep hills etc. but have never gone below 34 (my best is 47)
I believe that kind of mileage needs to be checked out.

Hope you enjoy the car

Danny

 

Note on Loaners: Frank Fletcher Toyota (in Joplin and it sounds like they were hard hit ) did give me a loaner for a tune-up and while they checked out my '09 Prius which went from 42 miles/gallon average to 30. I find most Toyota dealerships to be very unpleasant experiences but they were great except they could not find anything wrong with the car.

My Problem: So my car is getting 30 instead of 42. Doesn't matter the weather and I'm driving the same route I was when I was getting 42. The only thing is the battery died (didn't drive for a couple months due to registration issue) and when I started driving it again the mileage stank. I am driving much more carefully now trying to get great mileage but it isn't helping. Highway seems to be better and, although this is probably a problem with the gas gauge it does really, really well the first 120 miles or so (i.e. only two bars out of 10 disappear) then it just starts sucking gas. Or at least showing it.

Although Fletcher Toyota checked it over, not sure how much, Toyota is saying I have to pay for any more tests to determine if there is a problem. I spent $12,000 more over the Scion XB I really wanted because a 10-year analysis showed greater savings with the Prius. And now I get less mileage than my Dodge Colt at 1/4 the price. Toyota does not warranty the mileage it seems, and so far they don't really seem to care the car is not living up to their hype. If anyone else had a problem like this and somehow got it resolved can you post it? I will post any updates with the company and let you know if this gets resolved. I have a very bad feeling however that I have a lemon and Toyota is not going to care.

That aside, if you have to go to a dealership in the 4-state area I would recommend going a little out of your way to go to Fletcher, but wait until they get back on their feet from the disaster.

 

need info

If you want mileage help, please answer the questions at http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html by starting a new thread in the Gen II fuel economy area. You don't have a Gen III but responded to a Gen III thread..

A simple test though is to have the car totally warmed up and then take it on the highway, reset the MFD, set the cruise control and drive at a steady speed, at say 60-65 mph for 5-10 minutes. Tell us the mileage there.

We have little in the way of useful details from your above post. Trying to guess mileage based upon the "guess gauge" and how quickly it runs down is useless.

If your 12 volt battery went flat, it's likely you've killed it and it'll be need to be replaced. Some folks have had poor mileage w/bad 12 volt batteries and reported improvement after replacement.