As in any marriage... everything went fine at the beggining. Slow slow, the MPG/ tank started to drop, from approx. 55-56 first tanks to 45-46 now.

Car has 5k miles now, Oil is 50%, same gas pump, same driving habbits, tire pressure is 50 psi. no apparent changes, just lower mpg. Average temp. is kinda the same too.

What's going on?

 

Is this based on hand calculation or the trip computer?

 

both

 

for what its worth, i'm on my fifth tank and have noticed some things that may be affecting a lower mpg. first, i have noticed with my own driving that initially, i was driving the hch more carefully. slower than the speed limit, etc. after things have progressed, i've eeked up to over the speed limit very slowly over time. correspondedly, i've noticed my mpg adversely affected. i've since returned to my initial driving techniques and my mpg has jumped up to where it was originally. also, any rain or head winds dramatically affect mpg. we've had storms here the last tank and my mpg dropped noticeably. storms have passed now and mpg is back up. ensure that your a/c is off. sometimes the auto button gets pressed accidentally and the display doesn't say "a/c on" it only says "a/c off". you need to ensure that a/c is off and displayed. finally, my first few tanks included a modest extended highway cruise (about 150 miles) and my mpg was very high thus positively affecting my mpg for the tank. lately, i haven't done those trips and my mpg is slightly lower. even modest highway trips out of the norm will cause mpg to up as the ice in the hch is very efficient at highway speeds especially for extended periods.

let me know if you've noticed anything else as i'm in the same boat!

cheers,
neil

 

That's really odd. Normally the reverse would happen as the tires break in. In our HCH I's, most of us noticed mileage jumps at 3K and around 10K miles, but not the reverse. There are lots of things that will drop mileage, but nothing that would account for -10 MPG (aside from going say 70 degrees to 10).

This is only speculation here - but I've read in other threads about the new cars being shipped with an oil additive that somehow assists the break-in of the engine. Maybe this additive has some exceptional lubricating properties, but is now burning off as you put on more miles.

Aside from that, mileage killers are cold, traffic, and driving style. All those things being equal, I'd keep a close watch. Also, I'd only trust the hand calculations at the pump, not the display. I've heard the displays in the HCH II are not reliable - even mine has about a 3.2 MPG error margin.

 

Along with the other good suggestions, I'd ask - are you using your iFCD, or did you switch back to the temp display ? The accelerator is *very* sensitive to the amount of pressure you place on it, to the point where you can be thinking you're maintaining 50mpg, but the iFCD will show 40mpg. Just the slightest release of pressure will take you from maintaining that speed at 40mpg, to maintaining at 50mpg (a little more, and you can maintain the same speed > 50mpg).


When I first got the car, I watched the iFCD like a hawk, and was amazed at how sensitive the throttle / iFCD was, just to maintain speed. And from what I've seen, the iFCD is 'accurate', in that if you drive for awhile with it under 50mpg, your averaging display will drop / eventually read under 50mpg, as well.

I recently made my work commute w/o the iFCD, to see how I was doing, and while I didn't drop 10mpg, I did drop about 4+, as I recall. This was with about 3K on the car. 4mpg loss is a little much for me, so I set it back to the iFCD.

That's the only thing I can think of that would equal a 10mpg drop, assuming nothing else had changed, as you mentioned. If that doesn't work, schedule a service appt. The car may be running slightly rich, perhaps ?

 

maybe it's just me and the crazy traffic and usage + carpool lane which is abot 75mph all the time. dunno. I'll do a test on Sunday. on a route of 10 miles (home > office) which was a very good mileage approx. 70. I really doubt that I will get there more than 50. The car feels a bit heavy somehow, but I may be subjective now because this falling mpg.

I tought about the oil to. well, will live and tell... yesterday's partial total on trip computer was 47 for about 120 miles I did. Car has 5.3k Miles now. I asume oil will drop at 40% soon, as it's been at 50% for a while now...

 

Well, at least you are still getting far better FE than the vast majority of others with whom you share the road (myself included) As someone who is new to hypermiling techniques (albeit with a non-hybrid) I have noticed that it takes very little to "fall off my game" while driving for peak efficiency. In the very beginning I was concentrating hard and making huge gains. The past couple of days of slightly cooler weather plus a slight decrease in concentration have dipped my trip numbers by ~10%. In a HCH like yours the peaks are higher, making the lows look lower.

Good luck bringing it back up!

 

Forgive me if this was obvious, but is that 75 mph driving also new, or were you getting 55 MPG at that speed? 40 MPH is the cross over when wind resistance makes more of a difference than the car's friction parts. 50 MPH seems to be the upper range of the sweet spot. At 60, then 70 MPH you're using a LOT more energy to move the car. I forget the exact math or figures on the energy it takes, but if you Google on aerodynamics (or search here) you may find it. To me, 75 MPH alone would cause the 10 MPG drop, if that's what changed.

 

Release your hand brake.