Drop in fuel economy after a my Prius took a bump :(

So, I purchased my Gen iii Prius almost a year ago on 21/02/14 and it's been great! Until now that is..

A bit of background as I am a newbie to the forum. I purchased it with 42341 miles on the clock and just this evening when I got out of the car the odometer read 82019 - so I've travelled a few miles and spent quite some time in the cabin. When I purchased it I reset the trip A so I could monitor my mileage and although it's not perfect as it resets every 9999 miles it carries forward the MPG which currently stands at 60.5 over the 40k miles that I've nearly driven. I reset trip B after every fill up so I can see how I'm managing each tank of fuel. I don't drive the same route everyday and week. nor do I travel the same distance daily but somehow each week it averages at around 800-900 miles. Just before my "incident" I had just changed my tyres all round to Dunlop Sportmaxx RT which came with a C for Rolling Resistance, A for Wet Grip and 67 dB. After doing so I noticed that my fuel economy on trip B was starting to rise and the latest came out at 64.7 MPG. I was really looking forward to getting some great mileage.

Okay, I'll cut to the chase. So, two weeks ago whilst reversing onto a clients driveway the pavement rose up slightly and the clients driveway sloped downwards. I didn't quite notice that at the time so as I backed onto their drive the bottom of my car made an almighty scraping sound on the pavement. The scraping sound came from the area either immediately behind the front wheels or perhaps immediately in front of them. In my head I thought it must be either the exhaust or oil sump. I immediately stopped however I knew that the damage may have already been done and either needed to carry on reversing or drive forwards. I decided to drive forwards and parked up on the road. My car had taken a chunk of tarmac out of the pavement approximately 3 inches wide and a 1/2 deep. After waiting for some time there was no leaking oil and still isn't any. However I've been driving around for two weeks since then and my fuel economy over the last 4 fill ups has been consecutively low around the 54-55 MPG area - and that's with my best driving behaviour to increase fuel economy whereas beforehand I wasn't trying as hard. I finally managed to get into a garage on Friday who lifted it up and had a look at the entire underside. They brought me round to show me whilst it was up in the air. There's not a mark on the underside. No visual signs of damage or movement to any of the underside components. The only piece that was out of place was one of the plastic under engine covers at the very front of the car which was far from the suspected area and had a button clip missing which they replaced for me.

So this leaves me looking like I'm imagining things... But I'm not! There's something wrong with my poor Prius. I want to get it back above the 60 MPG and fix whatever it is that I've done wrong to it. Could it be the catalytic converter? The scrape that the car took certainly did something wrong but I just don't know what it could be. I'm considering taking it to Toyota to run one of their diagnostic tests but I'm not sure what that will show up and if it will show up what I did to it.

Any help would be greatly appreciated as it's so frustrating knowing what my car is capable of and not being able to achieve it because I've buggered it up somehow.

- Have you read This Thead Yet?
Yep

- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
60.5 Mpg based on my trip A reading which has carried almost 40k

- What fuel economy are you expecting and why?
60+ Mpg

- What are the approximate outside air temps?
10C

- How long are your trips?
At least an hour to reach each destination

How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)
Not sure, I will check and update or post

Have you had your alignment checked? Any pulling or abnormal tire wear?
I noticed a slight pulling to the left almost 3 months ago. It has changed or gotten any worse and I don't believe that it's the cause of the problem however it's booked in to be aligned next week so I'll update.

- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?
If my weekly average is 800 miles; 500 on motorway cruising at 70 mph, 300 on dual carriageways cruising at 40-50 mph and 100 miles driving through the city at around 30 mph

On a separate note, I use cruise control as much as possible and one thing that I find annoying is that I cannot set it at 20 MPH which would be really useful in city areas where speed cameras are constantly around. If anyone knows how to do that please let me know.

- What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)
It really is a mixture which is why I think my MPG used to be quite well balanced over the many miles that I travel

- What are your tire pressures?
42 PSi at the front and 41 PSi at the back, or whatever it says on the sticker on the drivers side door jamb

- Is your oil overfilled? (i.e. above the full mark on the dipstick)
It's just over 3/4 filled but not quite full.

- Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
BMW 320d which gave me around 42-44 mpg

- What region/state are you in? (if you haven't set your location)
London, UK

- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?
As sensible as possible without driving too slowly or holding people up behind me. I try and use the electric mode and pulse or glide when I can and allow the car to slow down on it's own whenever I can for as long as possible.

- What modes are you using, if any? "normal", EV, power, eco?
It's been in ECO mode around 95% of the time

- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?
Not as often as I should which I will now start doing.

- Are you driving using D or B mode?
I use D mode for driving. I have tried experimenting with B to slow down on hills or quickly when I need to, although I don't know if its good to use in general to save braking so I'll read up on that.

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?
No AC, just the heater or fan. Temperature on auto set to 22c

- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).
Dunlop Sortmaxx RT
C Rolling Resistance
A Wet Grip
67dB

- If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
I scraped the underside of my car which I believe to have almost immediately caused my drop in mpg

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Hi Bob, thanks for your response!

I don't think it was the tail pipe as all the brackets and the entire exhaust system was intact and mark free when the garage put it up on the ramp to take a look at it. The sound came from below the drivers seat as it is that area which I made contact with the pavement. I'm really baffled though as I saw with my own eyes that there wasn't a single scratch or mark on the underside that was new and indicating to be the culprit to my increase in fuel consumption.

When you say low speed and high speed benchmarks are you referring to running mpg consumption tests at both low and high speeds? I don't mind doing something like that although it needs to fit around my work diary. I have a 51 mile journey to my first client tomorrow morning of which 40 miles will be at 70 mph and the remaining will be at 30-40 mph. Then my next client is 38 miles from the first, again travelling 70 mph for 25 miles of the journey and around 30-40 mph for the remainder.

Sorry, I've just learnt that our gallons are different to yours. That explains why my mpg looks deceptively higher that what other people are achieving on here.... and here was me thinking that I just drove extra efficiently

 

Thanks, I've just ordered an odb2 reader as they're quite cheap and it would be useful to have one around.

 

Thanks for your reply.

I actually don't use electric only mode, what I meant was I use the electric engine as much as I can in slow moving traffic and in city driving where heavy acceleration isn't necessary.

Thanks for your explanation of engine braking. I won't bother using it, I'm better off timing my braking to help regeneration.

 

Thanks for your comments. I hope that you're right and it's just a normal swing of drop in mpg.

With regards to new tyres performing worse for fuel economy, I assume that you mean that they need a chance to wear in before they start delivering better fuel economy. I'd agree with this that they do need a chance to wear in, however I drive around 800 miles per week so they should have done so by now. Looking at the vehicle maintenance for tyre replacement as I reset it when I had new tyres put on, it's saying that I've now driven 2,268 miles these wheels so they should be worn in by now.

I'll be getting the alignment sorted this week. I hope that it resolves my issue as that would be great.

I'm also going to test the 12v battery level as the engine seems to be kicking in more often than I think it needs to when using the electric motor to drive at slow acceleration. My car is now 5 years old so I don't know if it's still the original battery or not but perhaps it does need a change. Hopefully the odb2 reader can tell me what the charge is otherwise I'll have to invest in a volt meter.

 

Okay, so I've figured out how to put my prius into vehicle diagnosis mode / service menu.

I went to "function check/setting" and then "vehicle signal".

My battery is 14.0v

When I turn my lights on nothing changed

When I window all four windows up and down the level changes to 13.9v and then returns to 14.0v

When I softly pressed the accelerator to fire up the engine the level momentarily changes to 13.9v then returns to 14.0v

I'll do some more research on battery levels and for a healthy battery but those readings seem to be okay to me at first glance.

 

Hi again!

You're quite right, C isn't great for fuel economy its just somewhere in between.

However the previous set that were on the car were budget tyres that the dealer had put on when they sold the car to me. I found the rolling resistance rating for them online to be an E rating so I was expecting better performance with the Dunlop set that I chose.

 

T

Thanks Fuzzy1! I turned off the Prius and pressed the on button without touching the brake pedal and went into the same menu. This time my battery reading is different.

It's currently reading 11.9v

If I turn my headlights on then it drops to 11.5v