poor gas mileage??

2003 Honda Accord (4cyl auto) in good shape, runs well, about 24000
miles. No maintenance on the car except oil changes and did one about
1000 miles ago. Front tires are replaced recently (back tires look
very good) so they are almost new condition but I'm not getting the
mileage I did on the highway. Once with a full load (4 passengers and
luggage) got around 37 mpg (mileage then was about 12,000 miles) and
about a month ago (same trip, mileage around 22,000 miles, less load)
got around 32 mpg and now for the same trip, I'm guessing a bit less
than that with less load. I'm guessing 27 to 29 mpg (I didn't fill
up yet). I drove it locally a little (35 miles) before taking to the
highway (300 miles) so I expect less than 37 but 27+ sounds a bit
severe. What do you guys normally expect to get on the highway for
this car?

I realize traffic, weather, load and speed have some bearing but just
so I don't overlook the obvious, what are the "simple" things to check
that I can replace and help improve the mileage? Off the top of my
head is the air filter. I'm not sure about the pcv valve or fuel
filter for mpg since the car runs well as far as I can tell otherwise.
I hate to mess with the engine more than I have to because I'm a bit
hesitant since I haven't done these type repairs in years and I never
worked on this car so the placement of things is kinda new to me.
Around town, it still averages around 24mpg which seems to be fairly
consistent since it was new. thanks

 

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Forget the fuel filter (read the service interval on that puppy). Put a
bottle of fuel injector cleaner in the tank two or three times per year.
Injectors that don't spray properly will not give good fuel mileage.

'Curly'

 

Do you have any objective evidence that the fuel injector cleaners do
any good? I mean evidence from people independent of the people making
and selling the fuel injector cleaner?

Or, alternatively, what is being cleaned? Wallets or injectors?

Jeff

 

Come on Jeff, I'm the one who asked for help and he was nice enough
to try. He's not asking whether I agree or you agree with him. I
understand your point and I'm not knowledgeable enough to say you are
right or wrong but it doesn't seem like it will break the bank to try.

 

All the same, I am skeptical that the injectors are the problem at
this tender age. Are you using crappy gas?

In my experience, mileage can bounce a lot from tank to tank for
reasons that are usually a mystery. Keep a log of every fill up and
you will get a better picture of what is happening.

You mention the new tires. They may have greater rolling resistance
or may be larger diameter (even if the same nominal size). We are
assuming they are properly inflated.

The temperature may have dropped significantly in the last couple
months depending on your location.

 

I think the biggest unknown is when you fill up your tank. Is it full or not?
The only way to REALLY find out is to keep topping it up until its spilling
out. Of course I would never recommend doing this, as it can cause MAJOR
problems in the EVAP system.

But the variance can be from 3-8 litres (1-2 gallons) which could affect
mileage in a 11 US gall tank by 10-15%.

t

 

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The VOLUME of the fuel (litres or gallons) is printed right on the
receipt. Whether the tank is totally full doesn't matter much.
Overfilling is bad from the fire department's perspective too.

'Curly'

 

OK... so what about the next time you fill up? Maybe the fuel froths a
little more this time and the tank doesn't get as full as last time. Means
your calculation will be better mileage on this tank.

Unless you actually know how much fuel is in your tank before you start
filling, you will never ACTUALLY know your correct mileage on that particular
tank. And there's no way to actually know how much is in there without
running the tank dry (bad for fuel pump) or draining it and measuring what
comes out.

Otherwise you have to settle for the variation I mentioned earlier.

t

 

Well, finally filled up and I got about 30.3 mpg so I guess that's
probably okay afterall because I did some 40 miles local driving on
this tankful of gas and the rest highway. I figure the 37 I once got
could be the extreme best with all things working for me including
perhaps newness of the car, tail wind, less traffic, etc... . My
guess is the 32 to 34 is the normal for me and less than that is for
misc. reasons. So while I think I might still check the air filter,
likely nothing else is in too bad of shape or need of replacement.
FWIW, the replacement tires are supposedly the same as the originals.

 

Air filter would be the thing I would focus in on most, without a
doubt.
Its not real cheap but, is fairly easy. Oh and I would think even 30
mpg, with the comfortable ride you get with an Accord, is really good.

Jim

 

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Air filter doesn't matter nearly as much as it did in the carburetor
days. A plugged air filter used to cause the carb to act as if the choke
was stuck ON, especially at higher speeds. Fuel would GUSH out of every
orifice as load increased. Mileage went south really fast.

Injected engines can cope better because the fuel is injected in a
metered manner and the computer figures out how much air is actually
flowing into the engine.

I once bought a Honda with a plugged air filter. It ran perfect.

'Curly'

 

I forgot to mention tho it's probably immaterial since all the highway
trips were about the same speed, I set the cruise control to about 73
mph. I suppose where I disengaged it and for how long might also make
a small difference for each trip. I don't recall exactly where each
trip I engaged and disengaged it. And as one person mentioned,
regardless of mpg, the ride is comfortable and cruise control works
well for these trips I take. One thing I have noticed is when the
oil has been changed it does increase my mpg tho in this case the oil
isn't that old in terms of mileage ... perhaps now 2000 miles or less
after this latest trip.