The tanks are 22 gallons, but you wont ever be able to fit 22 gals in it due to factor of safety involved and the air spaces they leave in the tank for expansion, etc. 18 gallons is about the max I have ever fit, empty with the light on and the computer saying 25 miles DTE.

 

yes, i have the SC 3865, and everything is calibrated

 

You know what I have noticed with the 3865. The overhead is more sensitive to anything like idling, acceleration, etc... I am going to check my MPGs when I fill up again and see if anything has changed since the last time I hand calc. I wonder if the tuning kinda messes the computers calculations up. To be honest I haven't been manually monitoring my MPGs since I tuned because I checked it before being tuned and it was with in the 0.5 MPGs like I stated before. I am going to look into this now.

 

Have you ever reset the overhead display??? My display reads 19-21MPG but, miles driven versus gallons used comes out to 18.5 MPG.

 

yep, reset a few times, always ends up in the same spot

 

I always had a readout of 11-12 after a few weeks on my display. Now with the 3865, after a few weeks after a reset, it reads 12-13. That's all city driving, so I really don't look anymore, just fill it up & drive.

 

I fill my 2005 every 200 miles. I never put in another penny's worth when the pump kicks off so I am somewhat consistent the way I fill up.

The overhead computer ALWAYS shows at least 1.5 to 2.0 MORE mpg than I am actually getting.

I have a 2008 Chevy Impala which is also about that far off.

I would assume it's simple math to divide the miles driven by the gallons to get your mpg.

Where am I going wrong???

 

Mine has been pretty close. last tank, readout said 16 avg. hand calc gave me 15.8. Guess these things are a little optimistic, either that or we're being ripped off at the pump

 

Dakotaff i feel a little better now.. Was starting to think something was wrong with my truck. Filled up tonight and this tank averaged 12.4 mpg. Didn't get below 14 until the winter..

 

Yeah I always do. The OM even claims you should reset it occasionally to account for changes in conditions, such as city, hills, etc.

Yep same here. Usually pretty damn close for me.