Gas mileage


#1

Our 2003 sequoia has always gotten poor mpg but my wife likes it, so what can I do, right? She checked it recently (gasp!) and it has gotten worse – down to 10 mpg from 18 mpg. Tire pressure? perfect. Plugs and wires? new condition and clean. Air filter and PCV valve? replaced and gained 3 mpg up to 13 mpg. I am thinking of replacing the EGR valve, but it is really expensive. Can I clean it with a solvent and reuse it? If it is not the EGR valve, maybe the valves? I am running out of ideas. Most of our mileage is local. My wife drives better than most men. I hot dog it and take it mudding much more than she does even though I rarely drive it. Oil is full synthetic and we have normally bought the same gasoline for years. It always starts right up and is otherwise in nearly perfect condition. We have not noticeably lost any horsepower over the last year. What do you suggest?


#2

I suggest you replace the thermostat . . . they can get stuck open after several years, which keeps the vehicle in open loop longer, which wastes more fuel


#3

I would also recommend replacing the upstream (in front of the the converter) oxygen sensors. They play a large part in fuel control, and just because there is no check engine light or fault codes doesn’t mean they’re good as new. A dirty or failing mass air flow sensor can also cause a loss of fuel economy.

Your locality hasn’t switched to ethanol fuel in the last year, has it?


#4

How is the mileage being checked?
Is it done with the gallons required to fill/number of miles traveled division method or is it by estimating a gauge reading or a dashboard readout?

How many miles on it? You state that you “hot dog it and take it mudding much more than she does” so the question of engine wear kind of comes into the picture.
Sometimes it doesn’t take much hotdogging and mudding to send things downhill.

The odds of this being related to the EGR are near zero in my opinion.


#5

You did not mention the mileage on the vehicle…If it’s over 100K miles, then Acemaster’s suggestion to replace the leading oxygen sensors has merit…These critical sensors don’t last forever and they control the fuel mixture…The EGR system is not a productive area for mileage improvement…A stuck brake caliper(s) can destroy mileage, but is usually noticed as a 'Hot wheel" problem…


#6

Thanks, guys! Mileage is coming up on 130K. MPG is being checked the old fashioned way, gallons required to fill and miles driven since last fill up. Gasoline is the same as it has been with 10% ethanol. My offroading in mountain grade is 3 or 4 times a year for an hour or so at a time using 4wd for maybe 30 minutes at a time and she does not take it off road. We live at 5000’ elevation and occasionally take it up over 7000’ around Flagstaff. We have never checked mpg after I have had it off road. Never had a squeak or hot wheels. No fault codes showing up either. Sounds like the oxy sensors are my next step. Any merit to using an additive to clean the valves / injectors?


#7

I think your chasing a ghost. www.fueleconomy.gov reports your 4WD truck getting 13 city, 16 hwy, 14 mixed. User reports have a 14.6 mpg average. Changing out these sensors may gain you 1 more mpg if your lucky. And Toyota wants a pretty penny for OEM O2 sensors.

My brother had one of these. He also loved the truck, but after gasoline hit $4.00 a gallon, he traded it in for a Camry.


#8

Oxygen sensors can be expensive, and I wouldn’t replace them without a reason (check engine light). Instead, I think you should look at the tires. You say they’re properly inflated, but if you changed tire models, the ones on your car might have more rolling resistance than the ones you replaced. Checking/replacing the thermostat could help too.

Think about what else has changed since the fuel economy worsened. Did you move from a flat area to a hilly area? Is your wife carrying more in the vehicle? Do you have a teenager or young adult driving this vehicle? Is your wife carrying more cargo than before, pulling a trailer, or using a rooftop carrier?


#9

hmm. I had not dug around to find out what our averages should be. Maybe I should be happy that it is not even lower than it has been. The thermostat now sounds like the better option since the upstream O2 sensors start at over $50 for two and are no fun to replace.

The four Michelins I put on there are about one year old and are rated at 60K mile. I do not know how to decide if they provide more resistance than the previous ones. I don’t even remember what knockoff brand they had on there when we bought the thing, but these are a couple inches taller and wider than the old ones were.

Our kids are bigger than a year ago and we have a new one but combined the three weigh 90 pounds. No other cargo and only pulled the boat twice this past summer. We are the only drivers and have lived here in the same terrain for 4 1/2 years.

Thanks, guys!


#10

If your tires are non-stock size, it’s going to be harder to calculate your fuel economy


#11

If your tires are not stock size in diameter, and you didn’t adjust your speedometer/odometer for the new diameter, you might just have an error in measurement of the miles traveled. Your wife might have been driving farther than she thought on each gallon of gas all this time. The added weight of a larger tire doesn’t help either.


#12

+10 a larger tire makes the odometer turn over less–giving a wrong reading, as the ever-wise Whitey noticed. Maybe not enough to go from 18 to 10, but a couple inches is a lot.
Try driving 10 miles with mileposts on an interstate, and see what your odometer thinks it is.


#13

Have you looked at your transmission fluid? You didn’t mention whether you had been maintaining it or not.

If you take it to a shop for oil changes that puts it up on a lift, have someone spin each wheel by hand to see if one has a lot of drag.

Is your temp gauge coming up to the same place it always has?


#14

OK. Changing tire size should affect the odometer reading – how obvious. See, this is why I needed help thinking through this. 13 mpg could easily equal 15 or so. Thanks a bunch.

I do most all the maintenance on our vehicles and this one has never been in a shop except to change tires. I have had it on my jack and each wheel spins freely. I pulled the tranny stick and it smells / looks perfect. Operating temp is normal, even nice and cool in July in the desert.


#15

With the wrong size tire, mileage will be totally inaccurate and it is calculated by the revolutions of one or more the tires and the actual tire size programmed into the computer as required by the factory specs. You cannot possibly get the correct odometer reading so all of your computing is a waste of time. Di you begin to notice the change in mileage when the tires were changed???


#16

First off of course, make sure you actually have a problem. Compare mpg on the same route and same driver, now, compared to before. Do it a few times. If you find the mpg actually has declined

  • Bring all owner’s manual suggested routine engine maintenance up to date.
  • Use a code reader to read all current and pending DTC codes.
  • Visually check that the thermostat opens at the right temp and correct dimension by putting it in a pan of hot water and looking at it as the water temp increases.
  • Test the engine coolant temp sensor used by the computer (ECM) for accuracy.
  • A thorough tests of all vacuum operated devices and hoses for vacuum leaks.
  • When the EGR fails, drivability problems are usually what is noticed first, or if it has stuck shut, that wouldn’t affect mpg. If the EGR remains a concern, it’s usually easy to test, you just apply vacuum to it at idle with a vacuum pump and if the EGR is working, the engine will severely stumble and usually stall.