Snoopy

Thank you Kornellred. I didn't want to go into detail because people believe what people believe.....as illustrated by some of the posts to this and other threads. A lot of misconceptions here.

And as far as I know (limited admittedly), you are dead on.

King Aires

Whoa, no one was saying that you or Kornellred or anyone else was wrong. Just some of us have anecdotal experience that cold air = poor MPG. We don't know why, we didn't state there was a reason, we just experience that.

I believe Kornellred is 100% correct, the DIC won't lie, it will tell you the mpg exact. That is if everything is working right. Don't forget that same DIC is telling me that I don't have any air pressure in my left front tire. But I believe that 99% of the time it is accurate.

So, his post does not refute any of the experiences we have had, I only use my DIC to calculate MPG and I can tell you that IT DOES confirm that cold ambient temps give me worse gas mileage.

Any thoughts?

Snoopy

Start at the beginning and read all the posts. You will probably understand what I have stated.

King Aires

Oh that is like 3 pages ago... I have gone too far to go back to the beginning

donbrew

Not to mention the computer uses the data it is given; if your tires are different than it is placarded for, the output will me incorrect. My mileage is a bit off because I run 215-60X16 tires and the placard is 215-55X16.

G I G O!

kornellred

For those who may care - and I do not think that there are many - I want to elaborate on my comment about the "dead nuts" accuracy of the DIC MPG figure. While my explanation of how most common fuel injectors work is basically correct, I stated that the flow rate of fuel through the injector is always a known quantity. That turns out to be true only if the fuel pressure is essentially a constant. In order for the fuel delivery pressure to be constant, a precision regulator would have to be employed, and there is no such apparatus in the fuel systems of the 2.2L and 2.4L Ecotec engines. There is an acceptable range of fuel pressure of 50 to 60 psig associated with the correct operation of the electric fuel pumps used in our HHRs. This means that the flow rate of fuel through the injector can vary somewhat depending upon fuel pressure, and that variation cannot be precisely measured (it need not be, either).
This seems to imply that the fuel consumption figure is a more complex calculation rather than a straight addition of known flow rates for time periods of specific duration.

The term ["dead nuts" accuracy] is a somewhat impolite colloquialism for a measurement that cannot be made any more precise. In terms of fuel consumption measurement accuracy with respect to DIC MPG readings, there may be room for improvement, but there is no reason to add the expense. The current level of accuracy is remarkably precise for all practical purposes.

Just sayin'......

Old Lar

I do it the old fashion way and calculate mpg. Rarely does the DIC match the calculated value. I will look at two DIC values: miles traveled and miles remaining and when they add up to 500, it indicates that I'm getting over 31 mpg. [( mt + mr)/16 gallons ] The DIC will read 29.

I don't collect DIC mpg data, but do collect the calculated values.

My overall MPG average (129,000 miles) has been 30.3 mpg with a standard deviation of 2.9 mpg.

11hhrlt

Time for an update. A few weeks ago there was a brief but significant
warmup here in the NE, from the teens to the 50's. At the same time as this
warmup, I took a 2 hour road trip to get some batteries (for a solar/backup
power system I'm putting together). The trip was @ 85% highway.

To start, I filled up with gas, checked tire pressure and zeroed the numbers
on the DIC. To my delight MPG starting climbing immediately. And really
started climbing on the highway. Just shy of 1 hour of driving, about the half-
way point, the DIC went from 25.1 mpg to 31.8 mpg (!). And it was still
climbing when I pulled off the highway to get the batteries. So what was it?
If the DIC is "dead nuts accurate", then there has to be a reason why the
sudden increase. Was it temperature? Or was it highway?

I'm not convinced it was highway driving alone. It was mentioned earlier in this
thread that maybe cold wheel bearings or cold transmission oil could be the
problem. The HHR is "stiff" and being held back. I think that's a very good point
since I've noticed mine too has quite a stiff, sluggish feel for a good 10 minutes
into a cold drive. Certainly something to consider.

And now about the batteries. I threw into the back of the HHR about 300
pounds of batteries ( By the way, don't try this at home. The plastic decking over
the spare tire started to buckle. I caught it just in time before I did any
real and permanent damage). Then back onto the highway I went. You can
probably guess what happened next. The DIC immediately started trending
downward and lost nearly all the MPG gained by the time I got home. I was
down to 27. 4 when I pulled into the drive (bummer). Forget about temperature.
And forget about highway. The added weight was a killer.

So what have I learned. The HHR is NOT a truck. That's what I was driving previous
to the HHR, for about 6 years. Nothing effected that thing (old Ford Ranger). Cold,
heat, weight, no weight, good gas, bad gas, nothing effected it. But the HHR is, well,
sensitive. You have to keep it warm and its' burdens light. Do that and, occasionally,
you can drive it hard for satisfaction. Be kind and gentle, too. Take care of it and it
will take care of you.

Gee, where have I heard that before?

Old Lar

You were driving down hill on the way over and up hill on the way back.

I'll see similar mpg fluctuations. I'll drive north on I-95 through central Florida and will see 31 mpg, but on the way south, the mpg drops?

King Aires

Or wind... we basically have giant boxes with wheels, very poor aerodynamic properties on this car.