Fuel mileage down - why?

[Sonataman]

I had been having a problem with my mpg going south and I ran 3 tanks of S1 back to back. Changed the oil today and it was BLACK! I mean it was REALLY black! Heavy gas smell along with that.
Talk about a sound and feel difference with fresh oil! Much quieter and smoother.

Still have not found the economy issue but it has been better lately, but still 10%+ down on what it normally got.

 

[simple_gifts]

In the north, we would all suspect a stuck thermostat especially in the winter months.

 

[4wheeldog]

Pardon my ignorance, but......What is S1?

 

[simple_gifts]

Originally Posted By: 4wheeldog
Pardon my ignorance, but......What is S1?


http://www.redlineoil.com/product.aspx?product=60103

 

[4wheeldog]

Has your fuel all been coming from a single station? If so, that is a variable you could change.

Otherwise, getting a read on what your mixture is, at the tailpipe, could be useful. You might have a bad O2 sensor.

 

[Kuato]

Originally Posted By: Sonataman
I had been having a problem with my mpg going south and I ran 3 tanks of S1 back to back. Changed the oil today and it was BLACK! I mean it was REALLY black! Heavy gas smell along with that.
Talk about a sound and feel difference with fresh oil! Much quieter and smoother.

Still have not found the economy issue but it has been better lately, but still 10%+ down on what it normally got.


3 tanks back to back?

Originally Posted By: "Redline website"
Cleans to nearly 100% efficiency in one treatment


It may simply take the oil change and some driving to clear it up. You didn't mention the vehicle/miles/etc so that would be helpful. If it's an older vehicle the O2 sensor might have given up as mentioned.

 

[Donald]

Your not going to get the best mileage in the winter.

Also while stations can use up to 10% for E10, they can use less. So you may have been getting gas that was 5% and now its 10%. You will get less MPG with E10 vs E5 vs E0.

 

[slipperysam]

Originally Posted By: Sonataman
I had been having a problem with my mpg going south and I ran 3 tanks of S1 back to back. Changed the oil today and it was BLACK! I mean it was REALLY black! Heavy gas smell along with that.
Talk about a sound and feel difference with fresh oil! Much quieter and smoother.

Still have not found the economy issue but it has been better lately, but still 10%+ down on what it normally got.


MPG is down and your finding a heavy fuel smell in your oil?
Your fuel is not burning in the combustion process entirely and is getting down into
the crankcase. Find out how that is happening and you'll likely solve your
problem. Maybe a compression test?

SS

 

[artificialist]

Using a scan tool and determining your coolant temperature is important. If the engine coolant temperature measurement is low, the engine will continue to run in open loop, even when it is warm. That causes an extra rich air fuel mixture, and replacing the oxygen sensor will make no difference if that is the case.

I'd also look into replacing the PCV valve, in case excessive blow by gas is entering the oil.