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Old 02-12-2014, 04:58 PM   #1
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More MPG info...

For starters, check out this site: http://ecomodder.com/
Lots of tips, ideas and experimentation on how to get better MPG, if that's something you're interested in.

Now what about the low, cold weather, mpg with the HHR. I did some research and data collection. And this is what I found out:

1. The outside ambient (the one in the front bumper) sensor is just a thermometer. It's a convenience item and has nothing to do with the ECM.
The 2 temperature sensors that matter are the coolant and the one in the MAF sensor. The coolant sensor you can see on the readout. The intake sensor you cannot. Assuming the ambient sensor is correct (and often it is not due to direct sunlight or road heat on the front bumper) that is the temperature of the air going into the motor.

2. The problem is the coolant temperature sensor bottoms out at 5 F. So the computer doesn't "recognize" anything below that. The other problem is the computer does not "recognize" idling, at least not in the way you might think. Over 6 consecutive cold engine starts with a 5 minute (exactly) warm-up period, under various temperature differences (-6 to 27 F) and under various loads (all accessories off versus all accs on), the DIC shows nearly the exact same amount of gas usage every single time (only 0.8 to 0.9 percent). In other words, the HHR's ECM applies a fixed variable to idling.

What this would mean, to me, anyway, is you absolutely cannot rely on the DIC to provide a consistently accurate measurement of gas usage. Better to rely on your own calculations.

The obvious question: why so poor gas mileage in cold weather? There has been much testimony supporting this. I think now the short answer is: that's just the way it is. The tried and true ways to get better mileage? Think friction, weight, resistance, drag, O2 density, etc, etc. Visit the ecomodder site. They offer all sorts of advice. And they do some very radical stuff.

In the meantime, I guess I'll just have to accept the HHR is not the gas sipper I expected... orrr, keep tire pressure up, the filter clean, drive slow, live and work close to a highway and move to a warm, dry climate. One could also try to fool the ECM into accepting a leaner (less gas) mixture going in. But that's far from a guarantee one would get better MPG, no matter what or how you do it.

I hope this was helpful.
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Old 02-12-2014, 06:28 PM   #2
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That is some very interesting data that you have gathered. Didn't catch the part in your post about what your actually mileage is and what you believe it should be.

And fwiw. My SS has the RPD that does give you the inlet temp. It will vary a few degrees from the ambient temp, depending on conditions.(yes, the picture is from back in warmer weather)
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Old 02-12-2014, 07:01 PM   #3
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Here's his original mileage thread....

https://www.chevyhhr.net/forums/problems-service-repairs-42/2011-hhr-lt-poor-gas-mileage-49369/

Of course it almost goes without saying, but the most accurate mileage computations are still the ones you do with paper and a pencil.
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Old 02-12-2014, 07:39 PM   #4
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Thanks Mike for the reference thread.
After reading it, it appears to me that really cold weather is just a killer as far as gas mileage is concerned for the HHR's. Don't know how you folks tolerate that cold stuff.

I'll just stay down here in the balmy South and get my 27-28 mpgs year round in my SS.
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Old 02-13-2014, 11:05 AM   #5
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Originally Posted by firemangeorge View Post
Thanks Mike for the reference thread.
After reading it, it appears to me that really cold weather is just a killer as far as gas mileage is concerned for the HHR's. Don't know how you folks tolerate that cold stuff.

I'll just stay down here in the balmy South and get my 27-28 mpgs year round in my SS.
Yes, thanks to Mike for clarifying.

My point was to offer, possibly, some insight as to why - that's a big "why" - the HHR suffers poor gas mileage in very cold weather. I thought, maybe, that I would find a temperature point where my HHR's 2.2 would show a marked decrease in efficiency. Was I able to find that out? According to the DIC, no. Would accessories on/off make a difference? According to the DIC, no. Can poor, cold weather gas mileage be attributed to long(er) and more frequent idling? I would tend to think so. But according to the DIC, no.

So the question remains: why such a significant decrease in cold weather performance and efficiency? And can that be improved? Right now, who really knows. I'd like to try to find that out, though. In the meantime, it's do what I can to maximize mpg.

Why am I sooo concerned about mileage? Because I am suffering from a minor and temporary case of buyer's remorse. I'll get over it.

Finally, you may have thought "Well, didn't you check the EPA estimates?" Of course I did. But the operative word is "estimate". I know for a fact my wife's car gets significantly higher mileage than the EPA estimate. And I've read lots of testimony the HHR will achieve averages in the 30+ range. So, yeah, the "low" average I'm getting is frustrating.
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Old 02-13-2014, 11:58 AM   #6
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One point.

If the ambient temp has nothing to do with the ECM, why does the OBDII report it?
Mine reports ambient and intake temps, they usually vary by about 20F after warm up. I'll go look up the PIDs if you want me to.

Another point.

The MPG computation is done mainly using the MAF and HO2 sensors, the computer knows what the air/fuel mixture is from the O2 sensors, then calculates the fuel usage from the actual air use. (incredibly simplified)
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Old 02-13-2014, 06:01 PM   #7
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Every car I have ever owned that I cared about mileage on has gotten less fuel economy in the winter than in the summer. I typically lose about 3-4 mpg during the winter. I only remote start my car for less than 30 seconds, usually when I am walking up to it. My wifes 2010 V-6 Camaro is done 2-3 mpg also from the summer.
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Old 02-14-2014, 02:31 AM   #8
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One point.

If the ambient temp has nothing to do with the ECM, why does the OBDII report it?
Mine reports ambient and intake temps, they usually vary by about 20F after warm up. I'll go look up the PIDs if you want me to.

Another point.

The MPG computation is done mainly using the MAF and HO2 sensors, the computer knows what the air/fuel mixture is from the O2 sensors, then calculates the fuel usage from the actual air use. (incredibly simplified)
To be honest Don, I don't know anything about how an OBD2 shows efficiency (using the leanest possible mixture without significantly affecting performance). The OBD2, I believe, shows sensor faults. Is that correct? Again, I don't really know.

The question is, I think, how rich is my HHR burning? Is it burning "too" much? Can it burn less? And how? My test data shows there's no way to know simply by looking at the DIC. Changing the variables does not change gas usage on the DIC. It's always 0.8 - 0.9%, no matter what you do. And why is it that the coolant sensor only reads down to 5 F (have to wonder)? Also, on 1 of 6 of my 5 minute tests the ambient sensor reported 39 F while the actual air temp (and the coolant temp) were the same at 23 F. Did that change the outcome? Nope. According to the DIC, the result was (yes) 0.8 - 0.9%. Doesn't make sense to me. And without talking to the ECM engineers directly - no doubt they are bound by confidentiality - my questions are likely to remain a mystery. I think in the end it will be much experimentation
- unless I get bored first or give up.

The bottom line: I might be able to live with it. But there's NO way I'm going to accept 22.3 mpg (current reading, if it's correct) is the standard for a 2.2, cold weather or not.
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Old 02-14-2014, 02:42 AM   #9
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I think you'll find that your fuel economy numbers will improve with the arrival of spring. All vehicles use more fuel in cold weather, you're up against increased rolling resistance, increased frictional losses, increased time spent in "Open Loop" operation until the engine reaches its optimum temperature, etc.

It's nothing to lose sleep over, and don't buy everything you see on various "Hyper Mileage" sites, some of their ideas fall straight into the realm of "crackpot science".

I have an old law school buddy who drives one of those Ford C-Max hybrids, he's a member of their forum and one of the members there went as far as clipping the little rubber nibs from the tire sidewalls in an effort to "cut drag".

Ryan did get a check from Ford when they got caught overstating the mileage on the C-Max cars, they sent him $450 to make up for the car's inability to break 42mpg when they said it would do 47mpg...guaranteed.

P.S. as I've said before in this discussion, and over the years, don't take the DIC mileage readout as gospel. A pencil and paper are more accurate.
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Old 02-14-2014, 08:21 AM   #10
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A.) 14:1 is pretty much maintained, or at least sought at all times.
B.) another winter gas burner is that the defroster runs the A/C, as does the recirc.
C.) OBDII shows all of the data that the "computer" will let out.
D.) I have found the MPG calculation to be exactly the same as my Excel spreadsheet, taking into account my 215-60X16 oversize tires.
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