Oil Change Intervals

The light comes on at startup at 4500 miles after the last reset as an early warning system of sorts for your maintenance interval. It stays on at 5000 miles.

Many things, especially weather, can affect fuel economy even with a consistent route and speed. For example, even minor differences in wind speed and direction can have a significant effect. Your changes are too small to draw any conclusions about, and I wouldn't worry about it.

Synthetic or lower viscosity oil are reported to offer minor fuel economy advantages (and I use Mobil 1), but the only way to demonstrate them conclusively would be through a controlled test with identical driving conditions, something the average Prius driver would find impractical, if not impossible.

 

Considering that most of your driving is at 70 - 75 mph, I would say that you are doing quite well to obtain mpg in the low-40s. If you really want to improve your mpg you would have to reduce your speed, but since you commute 100 miles a day I am sure that you are not interested in further lengthening your commute time.

 

try not to exceed 65, I have a 08 touring #6 and I have been getting 50mpg consistently with traffic,

w/o traffic I can get up to 52-53 +

 

Yeah. The change from 70 to 60 is quite remarkable. You get some improvement from 60 to 50, but it's probably not worth the headache of tailgating drivers (and is probably unsafe, anyway). However, if you can stay in the 60-65 MPH range and be gentle on the gas and brake, you should be able to get 50 MPG at the very least.

 

The HSD gets more inefficient over 65 MPH, so yeah, my experience is that 60-65 is best and 50 doesn't save much for the hours of you life you lose driving (Unless it's really scenic or you enjoy the relaxed pace.)

 

You're wasting your money on premium fuel - here's why:

The octane rating is a measure of how hard it is to ignite the fuel, not a measure of its "quality" or how much energy it contains. High compression engines require high octane fuel because they compress the air-fuel mix to a higher pressure and thus higher temperature. You don't want the mix igniting spontaneously (that is what causes a knock or a ping).

The Prius engine is designed for regular fuel, so it never compresses the mix that much.

I would start buying regular fuel, and pocketing the difference. -

PS - FWIW, I regularly get ~65 MPG on my commute using whatever regular gas I can find.

 

OK, it is good that you are buying fuel from mostly top tier vendors. However it is not good that you are using 91 octane. See the bottom of page 4-17 from the Hybrid 04 Engine file that can be found at:
Automotive Training and Resource Site

That page specifically warns against using octane greater than 87 as this may cause starting problems, while there is no mpg benefit.

 

As Patrick mentions, with 91 octane your engine may be gagging a little every time it starts and thus reducing MPGs. Use 87 octane only, and slow down a little.

 

I use Shell 87 only here is LA

 

As people have said, you are literally throwing your money away if you get 91 octane. Throwing it away. There is absolutely no benefit to running higher octane gas in a Prius. You should run 87 and, if you can find it, 85 is fine, too.

The importance of using "Top Tier" gasoline is debated, but probably has some benefit.

 

There was at least one report that using premium lowers MPG, and that using 85 octane gave better MPG than 87.

 

Thanks for the post on this. I just went over the 4500 mile mark and noticed the "Maint Reqd" light as well. Thought it may have something to do with the oil. I was planning on changing it at 5000 miles with Mobil 1 5W30.

I noticed that your using 0W30 as well. Any difference?