Fuel Economy Went South Suddenly

I have a '98 Odyssey EX. Over the last month or two, it has gone from
25mpg highway to 20. It's nothing obvious like a disconnected spark
plug or an underinflated tire. Any guesses what it could be?

 

Is it winter-like cold in your area? If so, that's probably why.

 

High Tech Misfit,

Can cold weather really cause a *20%* drop in fuel economy?

 

check/replace ignition componentry. check brakes are not binding. use
injector cleaner.

 

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Short trips with an engine that doesn't really get warmed up plowing
through snow with Winter Gas in the tank will KILL your gas mileage.

'Curly'

 

The last measurement covered mostly highway driving (75 miles nonstop
each way) on dry pavement.

 

My '96 Odyssey EX averaged 21.8 mpg over the first 94,000 miles before I
passed it off to a family member. It did get 25 on the highway, but only on
long trips when it was driven through entire tanks of gas (> 300 miles)
without stopping.

How long have you had this car? Do you have enough experience with it to
know the 25 mpg wasn't just a fluke?

 

E Meyer,

I've owned it since 2000 and driven it daily since 2003, and highway
mileage has always been around 25 mpg.

 

when's the last time you changed oil and air filter and the rest
plugs,wires,gas filter?? if nothing else look at your air filter..

 

Of course.

 

Just the drive to/from the highway can knock the average down 5 mpg.
The highway part of the trip was probably only a third to half of the fuel consumed on
the entire trip.

 

You need someone who knows how to analyze such problems with an OBDII
scanner. Also look for information on the problems on www.odyclub.com Search
the forums...

 

In that case, something has obviously changed with the car. If you didn't
change gas brands, didn't change your usage, and the gas company didn't
change their mix, then something has stopped working correctly in the car.
Some things to check would be temperature sensor(s), clogged air filter,
dirty MAF, O2 sensor(s), and of course all the normal tune up things (plugs,
distributor cap, rotor, wires, etc.). Basically the computer either thinks
the engine is not warmed up, so it adds more gas, or it thinks the mix is
too lean, so its adding more gas.