Gas mileage and headers

[Mike Frels]

At 03:38 PM 10/25/00 -0400, you wrote:
>I'm just wondering if I'm merely fighting slight weather change or if the
>headers have screwed with the tune.

Every year during the fall/winter months my car loses about 2-3 mpg. It 
also happens rather abruptly. All of a sudden my mileage drops. I have used 
Shell Premium 93 octane for the full life of the car so I cannot blame it 
on any other variables. It is an annual ritual that I do not look forward to.

I read something somewhere once that made some sense of this. I don't 
remember where but it said something about reformulated winter gasolines 
that run with a higher oxygen content so that during very cold warm ups the 
engine runs leaner and doesn't pollute as much. Well for those of use that 
have computer controlled cars with oxygen sensors it would seem that the 
reformulation of the gas is self defeating. With more oxygen content the 
sensor sees this and richens up the mixture. This of course would mean that 
my car would now use more gas to get what the computer says is the optimum 
mixture.

I don't know if what I have just said is fact or fantasy but I do know from 
my gas mileage experience and from what I have read that this is about the 
time for these "reformulated" winter grades to be distributed and for my 
mileage to drop. This could be what has happened to you a purely 
coincidental time.

Mike

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