Mpg decreasing

We don't know your geographical location, but suspect it is several factors:
1) new Prius owners-drivers
2) onset of cooler autumn-winter weather
3) Prius is not yet "broken in" with more than 10k mi (16k km)

Fuel economy always takes a drop with cooler-colder ambient air temperatures.

 

Also winter gas formulations in some areas can cause a drop in MPG. Around here that happens in October both last year and again this year I noticed a drop of 4-5 mpg from one tank to the next at this time of year.

 

Wow, 4-5 mpg drop just with different mixture. It's been hard enough getting over 50 and now I may have to try just as hard to get in the high 40s? Oh brother.

 

I noticed a significant drop in the mpg this last tank. I am certain it is the winter gas as everything else has stayed pretty much equal. I took a good 5 mpg hit.

 

I too have noticed a significant drop since we've been in these cooler temps. I've also noticed I take a big hit (more than usual) during my first 5 minutes of driving.

I was interested to see some threads about block heaters and radiator coverings to minimize the warm-up time at engine start.

I ordered a block heater. We'll see. . .

 

using the heater yet? that will make the ICE run more, and decrease MPG.

 

When I changed my first oil fill it looked much thinner than my 5W-30. I think that made my mpg drop a bit when I lost the break in oil.

Beyond that slight temperature differences have a big effect and not just the current temp when you start out in the morning. Battery temp will depend more on the min temp overnight.
Till it gets warm the engine races more and burns more fuel.

 

The good thing about the Prius is that it gets such good mileage. The bad thing about the Prius is that any little change in weather, road conditions, type of gas, or length of the trip has a greater adverse effect on the mileage than any other car. Ours has about 7800 miles on it and the ave. has been 45-48 mpg. When it's hot, the air conditioner lowers the mpg. When it's cold, the engine warmup lowers the mpg. When we get winter gas, the mpg goes down. When we installed better tires that wouldn't slip on wetr roads, we lost about 1 or 2 mpg. As near as I can tell, here in central WI, we have a small window of time in April/May & Sept/Oct when neither the heater or air conditioner are needed and summer gas is available that I can expect better mileage. With all of that said, the Prius is still the most efficient mid sized car available today. Because of the premium we have to pay to get the Prius (compared to other midsized non-hybred cars) I don't know which choice offers the best overall value, but it doesn't really matter though, because we have it now and in another year we'll probably have something else.

Doug

 

Wow, be careful with that sentence.
Let's hope for peace in this thread.

 

Most people quote the numbers they see on the sticker when they bought the car. They do not keep records. If you feel you can challenge them, they might start keeping records and learn. Almost no one I meet knows about the decreased milage with the seasons, decrease temps, changes in the formulation of gasoline.

 

another thing to check is the air filter.

 

Anybody thought of using the trick the Insight drivers use of putting in an air-dam infront of the radiator - blocking some of the air from passing over the radiator - so the engine stays warmer in the winter?

Then, your MPG stays higher.

It just hit near 80Fs here in Socal today and my MPG was back to high 40s (47-53s) again, when it was dropping to near ~45 last week when it was closer to 59F so it brough back this memory.

 

With no temprature gage how would you know if it were getting to hot. I guess the warning light would come on eventually but I would be reluctant to try it.

 

My last tank showed a 4 mpg drop and guess what I found, my right rear tire had a slow leak and it had dropped to 17psi. Fixed it, and now I am back to where I was. DON'T overlook the Obvious!!!

 

The Prius drive compartment is so tightly closed that very little uncontrolled air flows through it. Prius knows what engine temp it wants at any given operating condition and works to maintain that; interfering with its control mechanisms by blocking the radiator is not likely to help and may hurt.