DreamHHR

Here's the story, I don't quite know what to conclude of it yet...

Bought my HHR 2 months ago; as of the start of this week, it had ~ 4200 Km on the Odo. With my usual daily commute, and after the winter to summer gas switchover, I used to get a very consistent 8 l/100 (29.4mpg).

On Monday, I drove to Montreal and back (~500 Km) towing a small trailer. I took it easy, never really exceeded 105 Km/h. The trailer was empty for half of the trip, and on the way back I estimate that I was pulling a total weight of about 750 pounds, trailer included. I could feel the constant pull / drag from the trailer, but nothing unexpected. I got 8.3 l/100 (28 mpg) for that trip.

Now the surprising part: I refueled after the trip and reset the DIC; it's now estimating my daily commute at 7.3 l/100 (32.2 mpg). I still need to run a bit more gas through it to be sure, but I definitely see a trend down.

My hypothesis so far are:

1) I got a really good batch of gas
2) By towing the trailer for 500 Km, I sped up the "breaking in" on the engine and I'm getting the mileage of a 10000 Km engine.
3) I'm out of my mind and my next fillup will be back to 8 l/100.

The interesting part is that I can rule out 1 & 3 with time. I'll report back in a couple of weeks. I'm also changing the oil to synthetic next week, just in case the "breaking in" hypothesis verifies....

Any other explainations ???

Yves

Black Rose

The calculation jumps around quit a bit. For example, if do a round trip to the Kanata Costco via Hwy 416 & 417, I'll see around 9.2L/100km by the time I get home. If I do a round trip taking the streets, I end up with about 10.3, simply because of all the stop and go.

It's probably due to the average speed being raised by the trip to Montreal and back. The L/100km number will come down again over time as your average speed drops from local driving. Doing a highway run also certainly didn't hurt.

On the flip side, you are also at the mileage point where I noticed my mileage started to pick up. By about 11,000 kms it will take another little jump.

Snowdogs

I don't trust the DIC - even with reset after each fill. It's always 1-2 mpg off, it shows I'm getting higher than I really am.

I do see a difference in mine though between driving 65 to even 70 mph.

DreamHHR

No, no, I reset before the Montreal trip, and then again after my Tuesday morning fillup, so the Montreal trip has no impact. As expected, it moved quite a bit on Tuesday, less so yesterday, and today it looks to have settled at 7.3, all with my same typical daily commute (it hardly varies, and these numbers include some idling in traffic at the bridge), which is why I'm kind of stumped. (My current fuel range estimate + trip since fillup is > 850 Km)
I'm thinking that I may have finished breaking in my engine in a very short time. There has to be a reason that they tell you NOT to tow anything for the first 1000 miles...

I agree though, it's a bit too soon to conclude, and it may end up moving up a bit with the weekend shopping, but there's something there. I have a keen eye for these things. The car that I traded in for the HHR had a slipping clutch (not my doing!); I could bet you that nobody finds out about it for another year.

Yves

DreamHHR

Even if you don't trust it (I do, by the way, but that's beside the point), if you compare before and after values taken in the same conditions, you can still draw conclusions. If it makes an error, that error should be consistent (up or down) and not random.

Measuring MPG the old fashion way is not totally error-free either, unless you average over about 10 fillups.

Yves

dbarberaz

I am confused at the start you was getting 29.4 MPG during your trip down to 28 MPG and now your getting 32.2MPG and you stated it is going down
I will admit I think I failed the metric system in school, but you did the conversion for me in your post but I am still confused how it could be going down

Black Rose

Better gas mileage = less gas consumed (i.e. down).

dbarberaz

Never thought of it that way

Dave C

I can see your mileage going from 29.4mpg to 28mpg towing a trailer, but HOW does your DIC predict future MPG greater than you have been getting ? ? ?
My DIC only predicts DISTANCE (miles to next fill up)

It must gain something in the metric conversion


And whats with this l/100Km ?
Isn't that bacward thinking where less is more

DreamHHR

Yeah, it's down with the metric system (gas consumed per fixed distance), vs up with the english system (distance travelled per fixed gas volume).

To add to the confusion, imperial gallons (formerly used in Canada) are 20% larger than US gallons. So we get 20% better mileage.

Yves