Significant reduction in mpg

[bigk]

Folks - I have noticed over the last 2-3 months that my 2001 325i is giving a much lower mpg than normal. During my regular commute I was able to get about 400-420 miles per tank, and am now getting 340-350 miles. Nothing has changed, same commute, traffic patterns, gas used, etc. I understand variations in driving conditions, but this seems like it happened overnight and never corrected. I am continuously getting 340-350 now. that is an approximately 15% delta and is big

Any theories on how and why this can happen?

[Stinger9]

mileage on this car. Original owner? and what maintenance has been done on the emissions, air intake, MAS, O2 sensors, etc?
Which trans do you have?

[bigk]

90k miles, I am the original owner and hence can tell something aint right. Car gets routine annual maintanence as it always has. O2 sensors were replaced a while ago. There are no warning lights, etc.

Thanks

[122759]

I have a 2004 325i 5sp and I noticed the car going from a steady 30mpg to 27 last year. That's when someone mentioned they read that the formula that all gas stations use changes during the winter. Sure enough this winter it is the same 3mpg decrease. That may explain some of the loss your seeing.

[bigk]

I have owned this car for many summers and winters but have never experieced this. If this was normal, wouldn't we have huge swings in gas prices in the summer and winter?

[dembooks]

switch to a different brand of gas

use only 'Hi-Test" 91 or higher octane

replace the gas filter

replace the air filter

how many miles have the spark plugs been in there ?

have a fault code read-out by a BMW dealer

[Stinger9]

platinum plugs rated 100,000 miles?

[HBWT]

[dembooks]

because of the condition of the plug threads, threaded hole,
and just because you should look in there more often just
to be sure somebodies home

pay me now? or pay me bigger later ?? school of thought

[jayb]

[dembooks]

every 15,000 miles

depending on your climate,

letting your tank stay between 1/2 and EMPTY all the time
instead of keeping it 3/4 to FULL all the time to
prevent moisture build-up

how much rain you let into the filler during fill-ups

quality of storage tanks in the ground at yer station -
you don't know - that's why you replace the filter
BEFORE your car stops!

[bigk]

[rustyh]

for years. I can assure you there's no truth to it.

Joe

[rustyh]

Some very valid points you raise.

But, every BMW wrench I've ever heard comment on the plugs (dealer and indy + my Chapter's tech reps) seem to agree that the plugs should be good for anywhere between 75k - 100k miles. I replaced my wives ('02 325) at around 86k, and they looked brand new.

I can understand someone wanting to err on the side of caution and maybe change them at 60k - 70k or so, but why would you posit changing them at 30K??? I get more miles out of a plug than that on my tractor. :) (j/k)

Seriously though, 30k is nothing short of throwing away perfectly good plugs in my opinion. (we're assuming of course that nothing mechanical has happened that may have foiled a plug).

No decent plug (i.e. a plug that would be recommendable for these cars), regardless of what part of the country the person is in, should be shot at 30k miles.

Joe

[jayb]

You are a lucky man, how many wives have you had? And you replace them on a regular schedule, more power to you.

Could not miss the opportunity to pick up on that.

[dembooks]

if you have 'tried' to remove plugs that
have not been touched for 75 ...100,000 miles
(they're also used up) you'd understand

[jayb]

I agree that waiting for 100 k is too long. The problem that I have encountered is sometimes the plugs are locked in place. I do them between 60 and 80 k.

[Stinger9]

measure the fuel pressure with the engine off at the fuel rail Schraeder valve. Then let the car sit for hours and measure again to see if there is any bleed off.