Just got my new 2013 RDX with AWD a few days ago and was finally able to do some highway driving yesterday.

I set the cruise at about 75 mph and looked like I was only averaging about 20-21 mpg. I read on here that the only way to tell if the VCM was on would be would be a jump in the mpg gauge. Well that never happened. It's pretty flat where I live so it wouldn't have anything to do with hills. Am I doing something wrong?

 

Some are saying the VCM doesn't work above about 75, so you might have just confirmed it. If so, that's a bummer, since most of my interstate running is at or above 75.

 

If that is indeed the case then that is extremely disappointing to hear and makes me definitely rethink my decision to buy this car. Most of my highway driving is also 75-80 mph and the advertised gas mileage was a big reason why I purchased this car.

Why on earth would they set it up this way? I have a tough time believing the mileage would be better on 6 cylinders than 4 running 75-80 mph. I wonder if there's a way the dealership can tweak it? If not, I may seriously have to consider taking this thing back.

 

I think it's not that they set it up this way - it's physics. You're pushing a taller vehicle with more frontal area through the wind, and it reaches a point where 4 cylinders (or 3) have to work so hard to maintain the higher speed that it's actually better (and more economical) to run all 6 to maintain the speed.

Some people think 4 cylinders are going to automatically be more economical than 6 or 8, but that ain't the case. It works at lower speeds, but a 4-cyl engine will run out of grunt well before a 6- or 8-cylinder engine will. After all, it takes a certain amount of horsepower to push that vehicle along, and the higher the speed, the more power it takes.

I've had big V8's that just loafed along at 80mph, while a smaller V6 or I-4 would be spinning like a hyperactive squirrel in a cage to keep up. And many 4-cyl cars will start to lose fuel economy at higher speeds before a similar V6 will.

I'm really interested now to see how this all works. I'm going from the Dallas area to Phoenix and back very soon and will see what happens.

 

Also, remember the numeric readout is an average of all the miles driven since reset. If you fill your tank, reset the trip A odometer/MPG readout then immediately get on the highway you'll see the car is getting like 30 mpg, but if you drive around town for 200 miles and then get on the highway the MPG is reported lower as the highway mileage numbers are diluted by the city numbers in the computed and displayed average.

 

Not sure if ya'll were told this when you test drove, but when you have the car in "S" mode, it won't go into 6th gear automatically. You can put it in 6th using the paddle shifters, or you can put it in "D".

I'd be pretty disappointed if the instant read MPG was steady at 20 while cruising on flat terrain at 75 mph. My readout seems to show 18-50+ on the highway, averaging around 28

 

Hi Roadie2000, I just took a highway road trip through the Catskill Mountains. I set the cruise to 70 and averaged 27-28 mpg. I was very impressed going through many hills in my 3 hours of driving using 93 octane gas. Our highway speed limit is only 65 mph. I hope you have better success with your next trip

 

I was mainly going by the bar/gauge right under the numerical readout, if I'm driving at slower speeds I can usually see it jump up when the VCM kicks in but not on the highway. I'll be doing a lot of driving tomorrow and this weekend so I'll keep experimenting with it.

 

A little off topic but...This may or may not help to get the mpg average up. When I bought mine it had been city test driven and the MID stated 16.something. It was difficult getting the average much over 20-21 mpgs (MID) until I reset to clear mpgs at each fill. Then the average mpgs came up to where I would expect. Now, it's 24.5-26 with 80% hwy/20% city on premium (MID). Straight hwy @ 69 mph the MID read 31. BTW I've found my RDX-FWD MID estimates approximately .65 higher than hand calculated.

 

Yep, and the MID can be cleared at any time by pressing and holding the center (Select) steering wheel button. You need to do it separately for the "A" and "B" trip meters if you want both reset.

 

You can also customize both trip A and B to 1) reset when you fuel or 2) reset when the ignition is turned off. Otherwise the factory default is reset manually. No matter which way it is set up, the average fuel economy clears for that meter when it is reset. I have trip A set to reset when I fuel and reset trip B manually whenever I want to track miles driven between points or events. Page 87 of the online manual describes how to. I think the hard copy is the same.

 

the instant MPG is no indication of VCM working or not working. If youve had any other car with instant MPG, you can play with the throttle to show 100+mpg on a downhill with no throttle. This doesnt mean the car has VCM or if it did, that its working. I drive 75+ all the time and avg 26+ MPG no problem.

 

Thanks guys. I drove about 100 miles yesterday, mostly highway, and as you suggested I reset my MID a couple times. On my way back I was doing about 80 mph and I averaged over 26 mpg. On my way there I was going a little slower and averaged slightly better mpg, I was even getting around 30 at one point.

So, on the contrary to my original post, it looks like everything is operating as it should be and I'm actually quite happy with the mileage I'm getting.

 

^ Good to hear!