EV and Steath Mode

I have just over 19,000 miles on mine and my MFD is just about 3% higher than calulated mileage (miles driven/gallons pumped) for the life of the car. Most people find there's in a similar range, around 2 - 5% I think. So, it's not too shabby.

EV is electric vehicle mode and stealth mode basically refers to the same thing. You can engage EV on any Prius when under 42 MPH if it's fully warmed up. Basically, you just let up on the accelerator until you see arrows on the energy display only going from the wheels to the battery (regenerative breaking). Then you lightly apply pressure on the accelerator until there are only arrows going from the battery to the wheels (none from the engine).

There is an aftermarket mod where you can install a switch to force EV mode any time under around 35 MPH (I think). It's debatable whether you can save any gas doing this because whatever energy is used from the battery will be regenerated ultimately by the gas engine.

 

Agreed with Highly. Fuel economy and usage are calculated by the car mainly by monitoring fuel injector duration and operating frequency. Those of us who have tracked the difference between MFD MPG and calculated MPG over several tanks have found differences in the 2-4% range, so you're right in the ballpark.

Welcome to PriusChat and Prius-dom!

 

We must have hit "Submit" simultaneously.

It might seem counterintuitive, but to deliberately try to use the battery will cost you fuel economy. As Highly suggests, that energy must be replenished via the ICE, and with replenishment comes conversion losses. Better for normal driving is to use only ICE power for propulsion.

 

As you've probably figured out by now from the posts above, a calculated average mpg over many (10+) tanks of gasoline is likely to be more accurate than the MFD displayed average over the same number of tanks. On the other hand, the MFD is likely to be more accurate on any one tank or on an average over a few tanks.

This is largely because timing the fuel injectors gives a more accurate esimate of the amount of fuel used for one tank than trying to guess based on measuring the amount of fuel required to fill the bladder, whereas the largest likely error in figuring fuel used by measuring fuel added to the bladder is spread out having a decreasing affect on the calculation as the number of refills increases.

 

I wouldn't go that far. The ICE is only a 1.5L Atkinson cycle. It would be extremely sluggish and underpowered without the electric motors and its fuel economy would surely suffer substantially as a result. The beauty of the Prius is that it recaptures and uses a lot of the energy losses of a conventional ICE-powered vehicle. It's great that the Prius re-uses that energy when possible, but just don't go to extremes and draw the battery down excessively to try to get better MPG.

I think the best advice is to just let it do its thing for a while until you get used to it and can easily transition in and out of EV mode. Then you can decide if you want to start incorporating more advanced techniques, like pulse-and-glide.

 

Just a clarification:

While EV mode and Stealth mode are similar, they are distinctly different modes. EV mode can only be activated with a switch, which is missing on US spec vehicles. They can however be modified to add one, as the software is all still there. Stealth mode is also an electric only mode, but one that the car will naturally select under certain conditions. The EV mode has a hard limit of 34 mph, and is tolerant of harder acceleration and lower battery levels before the ICE will start. Stealth mode can be run to higher speeds, but unless the battery is very high you have to be very light on the accelerator to stay in stealth mode. The typical way to "select" stealth mode is to let all the way up on the accelerator then depress slightly. You should see just regen, then no arrows at all (glide mode) then electric only drive (stealth).

As mentioned before, using these modes in general will not help your MPGs, and will sometimes hurt. They are fun to play with though. There are a few situations when they can be handy. If you are gliding up to red light and need a little more boost to make it but don't want to start the ICE for example. I'll also use stealth on a long gentle down hill if I have a green battery after a long uphill. Feels like you can just coast forever! The real EV mode is really not good for much. Its handy if you want to move the car without starting the ICE. I believe the Toyota docs actually refer to this as ICE warmup delay mode, and thats pretty much all its for, moving the car around a parking lot or the like. About the only time I would actually use it is if you're coming home with a full battery, and know that you will get a good charge up in the morning due to a hill or the warmup cycle in cold weather. Of course its also good for sneaking up on people, as has been noted here:

Rob

 

MFD and MPG accuracy are discussed a little bit in the New Car
Features documents, which are available here. As an engineering
type you'll probably sit there for the next two weeks devouring
this stuff, because it's definitely a good read.
.
_H*