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Deterioration in Gas Mileage

3K views 7 replies 5 participants last post by  dr bob 
#1 ·
My wife drives our 2013 Pilot daily, so I don't get many opportunities to look it over, but we did some highway driving over the weekend and it looks like she's been averaging around 17mpg, which feels low. We are in a big city with a fair bit of stop and go traffic and she probably has a heavier foot than I, but according to my math based on the 160 or so highway miles we drove this weekend, that's about what it's getting. After filling the tank and driving all highway, we burned about a 1/4 tank (5ish) gallons in 80 miles with me driving using cruise control. It has about 48K miles, and I run a bottle of chevron with techron fuel system cleaner through it when I think about it, which isn't often. Any ideas as to what may be causing lower mileage? Thanks.
 
#2 ·
Really the only way to determine what kind of mileage you're getting is to fill the tank, drive, fill it again
(in a perfect world use the same pump) and divide the miles by the gallons. Using the analog guage to
determine how much gas burned is SWAG. Clearing the trip guages will get you closer to reality, but
still is not as accurate. On a road trip this summer that was 1,700 miles in length, the trip guages indicated
one MPG, and my computed number, using the actual gallons burned and miles driven for the trip, was within
.1 MPG of the trip guage.

My first step would be to run a can of Seafoam through the gas tank to keep things tidy in the fuel system. Some think it's snake oil, I think otherwise. Did the MPG slip over time, or was this an "all of a sudden" thing ?
Any codes thrown ? O2 sensors need replacing ?
 
#3 ·
Really the only way to determine what kind of mileage you're getting is to fill the tank, drive, fill it again
(in a perfect world use the same pump) and divide the miles by the gallons. Using the analog guage to
determine how much gas burned is SWAG. Clearing the trip guages will get you closer to reality, but
still is not as accurate. On a road trip this summer that was 1,700 miles in length, the trip guages indicated
one MPG, and my computed number, using the actual gallons burned and miles driven for the trip, was within
.1 MPG of the trip guage.

My first step would be to run a can of Seafoam through the gas tank to keep things tidy in the fuel system. Some think it's snake oil, I think otherwise. Did the MPG slip over time, or was this an "all of a sudden" thing ?
Any codes thrown ? O2 sensors need replacing ?
Unfortunately, I don't know if it slipped over time or all of the sudden. I did check the air filter and its housing for obstructions, and it was clear. I replaced the air filter about 8K miles ago. No codes have been thrown and no check engine lights are on; everything seems to be running fine.
 
#4 ·
Despite popular myths to the contrary, the air filter has virtually no effect on gas mileage. It affects performance, but only when the throttle plate is so far open that the air filter is the remaining air flow restriction. Bottom line is to move that to a very low spot on your reasonable-suspects list of things that you can change to affect fuel economy.

There are lists of things that do affect mileage though. Easy stuff like your tires and their inflation pressure affect their rolling resistance going down the road. Adjust pressure to what your door-jamb sticker shows, Junk-in-the-trunk syndrome means you are dragging unnecessary weight up to speed every time you accelerate or go up a hill. Don't let the luggage area become a storage closet. Fuel quality and seasonal fuel blend variations can affect economy by several percent over the course of a year. The biggest influence on fuel consumption is inside your right shoe, and in your head. Drive like you have raw eggs in your shoes. Keep engine RPM's as low as possible when accelerating, relaxing the throttle to induce earlier upshifts when launching and bringing the car to speed. My most-economical-cruise speed amazing coincides with the bottom end of the EPA's highway test protocol speed at about 48 MPH. Driving slower than that can increase fuel consumption almost as much as driving faster, since the transmission won't make it to top gear with locked torque converter at much lower than that. Keep your third and fourth eyes on the tach and the fuel economy display especially when driving in not-highway-cruise conditions, so you can adjust throttle pedal position up every time the opportunity presents itself. Also, learn to hate the brake pedal. Drive like you have no brakes available, anticipating slow-downs by lifting the throttle early rather than pressing the brake pedal later. In other words, drive like an old white-haired guy like me drives.

There are some mechanical deterioration and service things that affect consumption. The VCM cars sometimes suffer from piston and ring damage from cycling in and out of that mode. Honda has suggested that certain engine number ranges may have piston rings installed incorrectly, exacerbating a known VCM symptom that draws oil into the combustion chamber while VCM is active. If you see oil consumption in normal driving, it may be a symptom of problems soon ahead. The engine management system monitors for the misfire condition that results from that damage, and sets a trouble code and the MIL (check engine light) when it sees the symptoms. Honda has extended the engine warranty on several years of the gen-2 cars to help with this known issue.

Meanwhile... raw eggs in your shoes.
 
#5 ·
I also drive a 2013 Pilot 4wd. Over a six month period my highway driving from from 25 mpg to 20.5 21mpg. City went from 18 to 19 mpg to 16 to 17 mpg. Honda has no idea why. It now has 106,000 miles on it and it stated at about 65,000 miles to loose mileage. It sucks. I run tires at 36 psi. And have so called fuel efficient tires. Never had a car do this. And I've had a lot of cars. Had 3 Accords and they never did this. 4 Toyotas and they also never lost mileage like this one has.
 
#6 ·
Around town, I get 15-16 MPG. Understandable since I live in the aggressive NE corridor. If you dilly-dally and drive like an old lady around here, you'll get run off the road. The best I've gotten is 24 on a summer road trip out in the midwest. Nothing but straight, flat roads. I got better mileage when I had the VCMuzzler installed; probably because I wasn't trying to accelerate out of stupid ECO mode all the time.
 
#8 ·
Look in the sticky's at the top for some info. The VCMuzzler is a plug-in device that fools the ECM into preventing VCM activation. I've had one since pretty early in the program and I'm quite happy with it. Fuel economy was not affected, and driveability improved noticeably. A fringe benefit is that some VCM-related problems with cylinder damage seem to be avoided. No direct affiliation with the inventor but I'm a very satisfied customer/user.
 
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