New (to me) Prius Questions

I too have to agree with the others, it sounds like the tires to me. I am running the OEM Integrities and average just over 47.5 MPG. Your 12 volt might be weak, but I think it is the tires that are getting you more than anything. Now if you are driving 70 MPH or higher, that too will hurt the MPG.

 

hmmm has the Fuel filter ever been replaced ? often neglected (even by dealerships) and is obviously part of the chain of things that may effect fuel consumption, is there a roof rack fitted ?, definitely need to calculate by hand rather than he in car display, and maybe get someone else to drive it, not saying there is anything wrong with your technique but would be to eliminate it from the equation (obviously do not instruct them on how they should drive it)

 

did i read that correctly? 10.9V on ready and under load is not normal. it should register around 13.7 - 13.8V on ready mode as the HV battery takes care of charging the 12V battery.

 

My wife and I share a 2008 in southwest Ohio. In the winter we got just under 45 MPG. In the rest of the year we run around 48. Between the two of us I imagine we make about one average driver.

 

so we can probably rule out the 12v.. : )

just making sure:
1. do you drive off right away after starting up or wait for the engine to shut off by itself. When the battery is low in the morning, it's best to let the car do it's thing by warm-up cycle where it puts some charge to the HV battery as well.

2. do you end stage 3 manually (by pulling over or at a stop light and putting it in P) whenever you get the chance to stop for 5-10 secs? Sometimes, this helps a lot given the driving conditions and terrain you're in.

3. when you P&G, do you glide with no arrows or glide with arrows?

4. do you try and conserve momentum by cruising to the stop lights and not braking too hard unnecessarily?

5. does your foot demand a lot when you engage EV mode (assuming you have the EV mode button).

6. do you use cruise control all the way on your highway section?

 

Do read up on the Prius operating stages and take advantage of it whenever you can. Basically in the morning, it does this warm-up routine that momentarily isolates the ICE to do it's warm up that any demand to propel the car will be taken care of by the HV battery. If the battery is low (below 50%) and it gets drained getting up to speed, the ICE will have a harder time catching up on charging the HV battery back up to normal levels, thus using much more fuel than if you waited for it to end it's warm up stage and shut down by itself. Then you're ready to go.

But wait, there's more! You'll notice that 3-5 mins into your journey, the ICE will seem to refuse to shut down even if you let go of the accelerator trying to glide it. It's on the idle check stage 3 where the only way out of it is either your already well warmed up to operating temps and/or going downhill, or you override it manually by stopping for 5-10 seconds.

Use only CC if you're on flat or slight downhill grades. Using CC going up a hill will just gobble down unnecessary fuel trying to accelerate and maintain the set cruising speed all the way.

It's more economical to accelerate down, and decelerate slowly up.

Try these workarounds and see how you go on your next outing.

 

don't accellerate up a hill. that will cost you, who is saying it's a good idea? check the manual for fuel filter, i don't see it mentioned here much if at all. it's not in the first 100,000 miles for sure.

 

I'm getting 45.8 avg according to fuelly. I have Michelin Defender XT's. I also do not over-inflate my tires. I would assume that you should be getting better milage with what you are doing.


iPad ? HD

 

the concept is to gain as much momentum approaching the hill and try and maintain that momentum or slowly bleed off the momentum with little fuel used as possible while still being in a safe speed as u approach the summit. so just before u reach the summit, try to glide when u feel the car is already capable.

you must really be familiar with that hill or know how to read an approaching hill so u can plan ahead at what speed to approach it and at what rate of deceleration is needed to time it just right. also important is minimal footwork where it's mostly kept stationary at the lowest possible consumption rate or highest possible mpg rate (refer to instantaneous mpg reading) all the way, or slowly lifting off the accelerator in minute increments.

 

Nobody ever mentions that the Heater is the biggest contributor to lower then expected MPG's. Turn it off and you will see it rise quickly or use it very sparingly with a temp in the 65-69 range when its cold and a fan speed no greater then the 3rd button.

 

The fuel filter cannot be changed in the North American Prius unless you unless you replace the fuel tank, as it is built in to the tank with the fuel pump. This is not the cause of your low mpg. The air filter can cause higher fuel consumption but it would have to be very dirty.

John (Britprius)

 

+1 on the fuel filter, I was going to have mine replaced since we recently rolled over 100K miles. Its my SOP to replace it at 100K on every car I own... but no-go on the Prius. It, like the transmission fluid, is considered a lifetime part.

My bet is on the 12 volt battery. It should NEVER read 10-something volts even under heavy load. Your battery is new but bad, or is old and definitely ready for replacement. That would explain a drop of 5-8 mpg. After sitting overnight it should read 12.7 volts and under load at the very worst, upper 11 volts.

I don't think its your tires. The last set I had on mine were very sticky performance tires, because of the crap traction from the factory tires and the (loss of) traction control system. I only lost around 2 mpg (50 to 48 in the summer, 47 to 45 in the winter) because of them. I recently replaced the sticky tires with a different brand of performance tires with no change.

Not sure if you mentioned it, check your air filter. I used to tow with a Sienna, and suddenly on a trip I wondered why I had so little towing power and my mpgs were through the floor. Pulled the air filter and it was clogged with leaf bits. Replaced the filter and all was well.

 

My sister averaged 45 mpg on her 2005. My brother bought the car from her and promptly got 47 mpg. The two times I borrowed it, I got 57 mpg. Otherwise, the car is exactly the same. I hyper mile so it's no surprised what I get. My siblings drive the car normally. I notice my brother speeds up more gently than my sister.

 

All of the advice that everyone has given you is very good and will help with MPG. However, your 12Volt should not go down to 10.9 Volts under load unless you keep your light on for minutes, not seconds. Your 12 Volt is failing, probably when it sat on the lot before your purchase. You should get about 45MPG with the tires you currently have and approach 49-50MPG with proper LLR tires if you actually drive the way you described...

PS - 100,000 miles is a good time to change your spark plugs, too!

 

While I agree the battery is not in it's prime I calculate that the load applied to it " well over 60 amps," and more likely 80 amps by the OP it would not be unreasonable to expect the reading to be as low as 10.9 volts.

John (Britprius)

 

Go back to the dealer and insist on LRR tire. G/Y fuel Max, Energy Savers By Michelin and others. Your tires are your problem but have the alignment checked as well as tires.