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Silver Ghost II
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Discussion Starter · #1 ·
Does anyone note that the interior cabin of the 2012 V6 Coupes are a bit more warmer than the 2012 V6 Sedans. I've owned 4 different accord sedans, none had this issue. I have to run my A/C in 75 degree weather. Using the fan and vents won't keep the interior comfortable. By contrast, my 2012 V6 Sedan, says comfortable with the vents and fan, up to about 85 degrees. If you haven't figured it out yet, Honda's VCM works best with the A/C off and maintaining speeds between 65 - 75 mph. Going any slower does not completely engage the VCM, and using the A/C at any speed reduces fuel efficiency by 20%. So, if I can keep the A/C off, I'll gain about 20 - 25% better fuel efficiency, approaching 34 - 36 mpg, combined driving.
 

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The greater heat could be created by a greater greenhouse effect due to the larger rear window. The sedan’s windows let in less sunlight. And previous generation sedans may have let in even less light.

I found your observation about VCM interesting. It makes sense the engine must be under light load for VCM to engage. I’m surprised to hear that the added load of the A/C compressor can be enough to partially disengage VCM. I would not expect it to be that sensitive. And what I find more interesting is your comment that at below 65 mph VCM will not fully engage. I wonder if that is because the rpm are so low the engine has insufficient torque to operate on fewer cylinders.

Is a 20% fuel loss because of A/C correct? If your car gets 30 mph highway, a 20% loss would be 6 mpg. Running the A/C usually decreases fuel mileage by 2 to maybe 3 mpg. That would be more like a 6-10% loss. Or are you basing your 20% decrease in mpg on the combined loss created by a partially disengaged VCM and A/C drag when the A/C is on - a loss of 3 mpg for the A/C and another loss of 3 mpg for no VCM?

That raises another question, how much does VCM improve highway fuel mileage? I ask because according to my computer, on my last highway trip I got about 34 mpg at a steady 70 mph in my 6-6 which does not have VCM.

Circling back to your cabin heat issue, have you considered window tinting? If that contributes to less A/C use, your fuel mileage may increase. But do you really expect to get 34-36 mpg combined from a V6 Accord? That seems very optimistic to me.
 

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Can you get thermometer readings in both vehicles? Measure the temps coming out of the vents with the a/c off and compare.

Also - do both vehicles have the same type of seats? Cloth vs. leather feels different.

Lastly, something in your math is off. If you expect to get 36 mpg combined then does that mean that your sedan with a V6 gets nearly 42 mpg highway?

EPA ratings for V6 - 29 highway for coupe automatic, 30 for sedan.

I can eke out 34mpg highway in my V6 auto coupe but that is with cruise control and never stopping for anything but gas.
 

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I don't think you're going to get that gas mileage either. I don't get that in the 4 cylinder. I did achieve these numbers in an 89 coupé 4 cylinder (1.8L).
 

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Honda Nation
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You do not lose 20% of your fuel economy with your A/C on. At most it's 5-6%. You're driving a 2012 Honda Accord, not a '68 Cadillac.

If you are losing 20% in fuel economy you are doing something else, changing driving style, or there is a problem with your car.
 

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Silver Ghost II
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Discussion Starter · #7 ·
OK. I did not graduate from MIT with a PHD in Mathematics, so the MPG math may not be exact. Here are some facts: The 2012 EX-L/Navi V6 Coupe [Car in question] achieved 26.4 mpg avg over 16,581 miles. On a recent trip from Ontario Ca up the I15 to Salt Lake City Utah, 1428 miles round trip, 32 mpg, avg, speed 75 mph. 89/91 octane, heater on, a/c off. [car burned an average of 2.5 gallons of fuel per hour, during an 9 hour trip, 22.5 gallons of gas one way]. I can't speak to another V6 Coupe, but, the VCM in my 2012 V6 Coupe operates fully above 70 mph, and between 60-65 in my Wife's 2012 EX-L/Navi V6 Sedan.

In a work week, I travel 400+ miles and I fill up with 16.8 gallons on average. By my math, that's inline with the average mpg over the life of my coupe, especially in Southern California, Ontario Area, using the A/C.

I will measure the heat difference in the coming weeks. My suspicion - smaller interior volume. BTW, Side, quarters and back windows tinted 20%. I also think this heat issue is just an oddity like stalled starts and acceleration spurts with minimal pedal input I experience every blue moon. Was just wondering if any other coupe owner felt more than normal heat in the cabin. And the VCM discussion is just from my experience, and has no bearing on the design of the system, it's effectiveness to achieve better fuel economy or how it affects other drivers - just how it has been working in my 2 2012 EX-L/Navi Accords.
 

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Honda Nation
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OK. I did not graduate from MIT with a PHD in Mathematics, so the MPG math may not be exact. Here are some facts: The 2012 EX-L/Navi V6 Coupe [Car in question] achieved 26.4 mpg avg over 16,581 miles. On a recent trip from Ontario Ca up the I15 to Salt Lake City Utah, 1428 miles round trip, 32 mpg, avg, speed 75 mph. 89/91 octane, heater on, a/c off. [car burned an average of 2.5 gallons of fuel per hour, during an 9 hour trip, 22.5 gallons of gas one way]. I can't speak to another V6 Coupe, but, the VCM in my 2012 V6 Coupe operates fully above 70 mph, and between 60-65 in my Wife's 2012 EX-L/Navi V6 Sedan.

In a work week, I travel 400+ miles and I fill up with 16.8 gallons on average. By my math, that's inline with the average mpg over the life of my coupe, especially in Southern California, Ontario Area, using the A/C.

I will measure the heat difference in the coming weeks. My suspicion - smaller interior volume. BTW, Side, quarters and back windows tinted 20%. I also think this heat issue is just an oddity like stalled starts and acceleration spurts with minimal pedal input I experience every blue moon. Was just wondering if any other coupe owner felt more than normal heat in the cabin. And the VCM discussion is just from my experience, and has no bearing on the design of the system, it's effectiveness to achieve better fuel economy or how it affects other drivers - just how it has been working in my 2 2012 EX-L/Navi Accords.
When it's 75 out I don't use my A/C either. I might have my moonroof open but the A/C isn't needed. And I have black leather. A/C isn't a requirement for me until it's in the mid-80s.
 
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