Unfortunately this time the mileage dropped about the time my gas tank vent
lines went so it's a bit confused but the mileage has been down for at least
4 tanks.  Pretty much the same type of driving and the same stations used
for fill up.

I'll try this tank then I think I gotta go look for what might be wrong.
Maybe I can find out why the van doesn't idle high when dead cold but does
when started warm sometimes too.

Mike

On 12/5/02 6:14 PM, "Joel Walker" <jwalker17@earthlink.net> wrote:

>> Every once in a while my gas mileage drops 20+%, from
> 18 to 15 around town
>> for example.  Then it will go back up.  Nothing done
> to van.
> Checked O2 sensor and it's OK every time.
>> Any ideas?
>> If it's bad grounds can I just shoot the damn thing
> and be done with it?
>
> could be the station and the pump nozzle. really. if
> you let the nozzle click-off and do NOT fill any
> further yourself, you can easily be off several mpg on
> any given tank ... it just depends on which station you
> filled at last, and which one you're filling at now.
>
> example.
>
> drive 230 miles, fill up at station A. nozzle puts in
> 13 gallons before it clicks off.
> 230/13 = 17.7 mpg.
> now drive 230 miles, fill up at station B. nozzle
> allows 14 gallons before it clicks off.
> 230/14  = 16.4 mpg.
> and both times, you might have actually 'needed' 14.5
> or 15 gallons to 'fill up'.
> some nozzles are worse than that ... and can make 2 or
> 3 mpg difference.
>
> even if you fill it up yourself, you can easily be off
> 0.5 gallons from one time to the next.
>
> so the trick is to watch the average per tank, and
> compare each tank to that average. as long as it's
> close to the average, either over or under, you're ok.
> when a trend of lower mpg starts being noticed ... 2 or
> 3 tanks below the average by a couple of mpg ... then
> you need to start looking for problems.
>
> also, cold weather and how long you let it warm up in
> the morning (or at work, before going home) can make a
> big difference. a short 20-mile trip on the highway can
> raise your per-tank mpg by 1.5 to 2.0 mpg.
>
> good luck!
> joel
>